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<!-- DFS ActiveDisclosure(SM) XBRL Linkbase Document - http://www.dfsco.com/financial-services/ -->
<!-- Creation Date      : 2019-03-06T08:27:31.6148514+00:00 -->
<!-- Version            : 3.3.6989.14284 -->
<!-- Package ID         : e4f7c612abf244a6aaf4b653cc07da0f -->
<!-- Copyright (c) 2019 Donnelley Financial, LLC. All Rights Reserved. -->
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    <label xml:lang="en-US" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Expense And Other Assets Current</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current assets</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and equipment, net</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Net</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets Noncurrent</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Assets" xlink:type="locator" xlink:label="us-gaap_Assets" />
    <label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">LIABILITIES AND STOCKHOLDERS&#8217; EQUITY</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities And Stockholders Equity [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current liabilities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:type="locator" xlink:label="us-gaap_AccountsPayableCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable Current</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued and other liabilities</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued And Other Liabilities Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccruedIncomeTaxesCurrent" xlink:type="locator" xlink:label="us-gaap_AccruedIncomeTaxesCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedIncomeTaxesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income taxes payable</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedIncomeTaxesCurrent" xlink:to="us-gaap_AccruedIncomeTaxesCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedIncomeTaxesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Income Taxes Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:type="locator" xlink:label="us-gaap_DeferredRevenueCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unearned revenue recognized under units-of-revenue method</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueCurrent" xlink:to="us-gaap_DeferredRevenueCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:to="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current portion of long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtCurrent" xlink:to="us-gaap_LongTermDebtCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:type="locator" xlink:label="us-gaap_DeferredRevenueNoncurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unearned revenue recognized under units-of-revenue method &#8211; long-term</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueNoncurrent" xlink:to="us-gaap_DeferredRevenueNoncurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue Noncurrent</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtNoncurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtNoncurrent" xlink:to="us-gaap_LongTermDebtNoncurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Noncurrent</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:type="locator" xlink:label="us-gaap_OtherLiabilitiesNoncurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other liabilities &#8211; long-term</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherLiabilitiesNoncurrent" xlink:to="us-gaap_OtherLiabilitiesNoncurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities Noncurrent</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Liabilities" xlink:type="locator" xlink:label="us-gaap_Liabilities" />
    <label xml:lang="en-US" xlink:label="us-gaap_Liabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_Liabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingencies" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies (Note 14)</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders&#8217; equity:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PreferredStockValue" xlink:type="locator" xlink:label="us-gaap_PreferredStockValue" />
    <label xml:lang="en-US" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible preferred stock, $0.05 par value, 1,000,000 shares authorized, 6,256 and 5,003 shares issued and outstanding at December 31, 2018 and 2017, respectively</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Value</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockValue" xlink:type="locator" xlink:label="us-gaap_CommonStockValue" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, $0.0075 par value, 277,333,332 shares authorized, 8,690,723 and 8,249,158 shares issued and outstanding at December 31, 2018 and 2017, respectively</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Value</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapital" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
    <label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated deficit</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings Accumulated Deficit</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockholdersEquity" xlink:type="locator" xlink:label="us-gaap_StockholdersEquity" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total stockholders&#8217; equity</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Income Loss Available To Common Stockholders Basic</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Income Loss Available To Common Stockholders Diluted</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basic net (loss) income per share available to common stockholders</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share Basic</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share Diluted</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average shares used in computing basic net (loss) income per share available to common stockholders</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number Of Shares Outstanding Basic</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average shares used in computing diluted net (loss) income per share available to common stockholders</label>
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    <label xml:lang="en-US" xlink:label="xoma_SharesReleasedOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to release of restricted stock units (RSUs) in shares during the period.</label>
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    <loc xlink:href="xoma-20181231.xsd#xoma_ReleaseOfRestrictedStockUnits" xlink:type="locator" xlink:label="xoma_ReleaseOfRestrictedStockUnits" />
    <label xml:lang="en-US" xlink:label="xoma_ReleaseOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">This element represents the amount of recognized equity-based compensation related to restricted stock units released during the period.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ReleaseOfRestrictedStockUnits" xlink:to="xoma_ReleaseOfRestrictedStockUnits_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PreferredStockIssuedDuringPeriodSharesNewIssues" xlink:type="locator" xlink:label="xoma_PreferredStockIssuedDuringPeriodSharesNewIssues" />
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of preferred stock shares issued during the period.</label>
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    <loc xlink:href="xoma-20181231.xsd#xoma_PreferredStockIssuedDuringPeriodValueNewIssues" xlink:type="locator" xlink:label="xoma_PreferredStockIssuedDuringPeriodValueNewIssues" />
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Equity impact of the value of new preferred stock issued during the period.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PreferredStockIssuedDuringPeriodValueNewIssues" xlink:to="xoma_PreferredStockIssuedDuringPeriodValueNewIssues_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementOfStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Stockholders Equity [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfStockholdersEquityAbstract" xlink:to="us-gaap_StatementOfStockholdersEquityAbstract_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-In Capital [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_StatementEquityComponentsAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Equity Components [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_EquityComponentDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockMember" xlink:to="us-gaap_CommonStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-In Capital [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapitalMember" xlink:to="us-gaap_AdditionalPaidInCapitalMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Deficit [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsMember" xlink:to="us-gaap_RetainedEarningsMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:type="locator" xlink:label="us-gaap_StatementClassOfStockAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_StatementClassOfStockAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Class Of Stock [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:type="locator" xlink:label="us-gaap_ClassOfStockDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_ClassOfStockDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Stock [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:type="locator" xlink:label="us-gaap_ConvertiblePreferredStockMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertiblePreferredStockMember" xlink:to="us-gaap_ConvertiblePreferredStockMember_lbl" />
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Line Items]</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance (in shares)</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Outstanding</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase (Decrease) in Stockholders&apos; Equity [Roll Forward]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Stockholders Equity Roll Forward</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1" xlink:type="locator" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1" />
    <label xml:lang="en-US" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative effect adjustment to accumulated deficit due to adoption of ASU 2016-09</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Stock Options Exercised</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" />
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" />
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:to="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Share Based Compensation</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock related to 401(k) contribution and ESPP (in shares)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" xlink:to="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Share Based Compensation</label>
    <label xml:lang="en-US" xlink:label="xoma_ReleaseOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting of restricted stock units</label>
    <label xml:lang="en-US" xlink:label="xoma_ReleaseOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Release Of Restricted Stock Units</label>
    <label xml:lang="en-US" xlink:label="xoma_SharesReleasedOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting of restricted stock units (in shares)</label>
    <label xml:lang="en-US" xlink:label="xoma_SharesReleasedOfRestrictedStockUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Released Of Restricted Stock Units</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of warrants</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Additional Paid In Capital Warrant Issued</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of convertible preferred stock</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Issued During Period Value New Issues</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of convertible preferred stock (in shares)</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Issued During Period Shares New Issues</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value New Issues</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock (in shares)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares New Issues</label>
    <label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income (loss) and comprehensive income (loss)</label>
    <label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance</label>
    <label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance (in shares)</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement" xlink:type="locator" xlink:label="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value of common stock shares received as consideration for license agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement" xlink:to="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan" xlink:type="locator" xlink:label="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License fee recognized related to repayment of principal and accrued interest under loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan" xlink:to="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims" xlink:type="locator" xlink:label="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims" />
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Defined contribution plan issuance of Common stock for services or claims.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims" xlink:to="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_GainLossOnSublease" xlink:type="locator" xlink:label="xoma_GainLossOnSublease" />
    <label xml:lang="en-US" xlink:label="xoma_GainLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Gain (loss) on sublease.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_GainLossOnSublease" xlink:to="xoma_GainLossOnSublease_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod" xlink:type="locator" xlink:label="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod" />
    <label xml:lang="en-US" xlink:label="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Increase (decrease) in unearned revenue recognized under units of revenue method.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod" xlink:to="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement" xlink:type="locator" xlink:label="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Purchase of royalty rights in connection with purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement" xlink:to="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EndOfTermFeePaidToLender" xlink:type="locator" xlink:label="xoma_EndOfTermFeePaidToLender" />
    <label xml:lang="en-US" xlink:label="xoma_EndOfTermFeePaidToLender_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The cash outflow for end-of-term fee paid to the lender.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EndOfTermFeePaidToLender" xlink:to="xoma_EndOfTermFeePaidToLender_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Cash Flows [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from operating activities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProfitLoss" xlink:type="locator" xlink:label="us-gaap_ProfitLoss" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProfitLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net (loss) income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProfitLoss" xlink:to="us-gaap_ProfitLoss_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProfitLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Profit Loss</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Fair value of Rezolute common stock shares received as consideration for license agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Of Common Stock Shares Received As Consideration For License Agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">License fee recognized related to repayment of principal and accrued interest under the Servicer Loan</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Fee Recognized Related To Repayment Of Principal And Accrued Interest Under Loan</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensation" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock contribution to 401(k)</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Issuance Of Common Stock For Services Or Claims</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:type="locator" xlink:label="us-gaap_DepreciationAndAmortization" />
    <label xml:lang="en-US" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationAndAmortization" xlink:to="us-gaap_DepreciationAndAmortization_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation And Amortization</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts" xlink:type="locator" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts" />
    <label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of debt issuance costs, debt discount and final payment on debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfFinancingCostsAndDiscounts" xlink:to="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Of Financing Costs And Discounts</label>
    <label xml:lang="en-US" xlink:label="xoma_GainLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Loss on sublease</label>
    <label xml:lang="en-US" xlink:label="xoma_GainLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Gain Loss On Sublease</label>
    <label xml:lang="en-US" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Loss on extinguishment of debt</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized" xlink:type="locator" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized" />
    <label xml:lang="en-US" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Realized (gain) loss on foreign currency exchange</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ForeignCurrencyTransactionGainLossRealized" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossRealized_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Foreign Currency Transaction Gain Loss Realized</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges" xlink:type="locator" xlink:label="us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges" />
    <label xml:lang="en-US" xlink:label="us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net gain on sale, disposal and impairment of equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges" xlink:to="us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Gain Loss On Sales Of Assets And Asset Impairment Charges</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:type="locator" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" />
    <label xml:lang="en-US" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in fair value of long-term equity securities</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Securities Fv Ni Unrealized Gain Loss</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherNoncashIncomeExpense" xlink:type="locator" xlink:label="us-gaap_OtherNoncashIncomeExpense" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherNoncashIncomeExpense" xlink:to="us-gaap_OtherNoncashIncomeExpense_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Noncash Income Expense</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in assets and liabilities:</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Operating Capital [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInReceivables" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInReceivables" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInReceivables_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Trade and other receivables</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInReceivables" xlink:to="us-gaap_IncreaseDecreaseInReceivables_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInReceivables_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Receivables</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Prepaid expenses and other assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Prepaid Deferred Expense And Other Assets</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Payable And Accrued Liabilities</label>
    <label xml:lang="en-US" xlink:label="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Unearned revenue recognized under units-of-revenue method</label>
    <label xml:lang="en-US" xlink:label="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Unearned Revenue Recognized Under Units Of Revenue Method</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax payable</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:to="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accrued Income Taxes Payable</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Other Operating Liabilities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash (used in) provided by operating activities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from investing activities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:to="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Sale Of Property Plant And Equipment</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Property Plant And Equipment</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of royalty rights in connection with Agenus purchase agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Purchase Of Royalty Rights In Connection With Purchase Agreement</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash (used in) provided by investing activities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from issuance of convertible preferred stock, net of issuance costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" xlink:to="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Convertible Preferred Stock</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from issuance of common stock, net of issuance costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Common Stock</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:type="locator" xlink:label="us-gaap_ProceedsFromStockOptionsExercised" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from exercise of options</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromStockOptionsExercised" xlink:to="us-gaap_ProceedsFromStockOptionsExercised_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Stock Options Exercised</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from issuance of long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:to="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Long Term Debt</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsOfFinancingCosts" xlink:type="locator" xlink:label="us-gaap_PaymentsOfFinancingCosts" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsOfFinancingCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Debt issuance costs and loan fees</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsOfFinancingCosts" xlink:to="us-gaap_PaymentsOfFinancingCosts_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsOfFinancingCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments Of Financing Costs</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:type="locator" xlink:label="us-gaap_RepaymentsOfLongTermDebt" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Principal payments &#8211; debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermDebt" xlink:to="us-gaap_RepaymentsOfLongTermDebt_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repayments Of Long Term Debt</label>
    <label xml:lang="en-US" xlink:label="xoma_EndOfTermFeePaidToLender_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Payment of final fee related to loan extinguishment</label>
    <label xml:lang="en-US" xlink:label="xoma_EndOfTermFeePaidToLender_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">End Of Term Fee Paid To Lender</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:type="locator" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Principal payments &#8211; capital lease</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repayments Of Long Term Capital Lease Obligations</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Taxes paid related to net share settlement of equity awards</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:to="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments Related To Tax Withholding For Share Based Compensation</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by financing activities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EffectOfExchangeRateOnCash" xlink:type="locator" xlink:label="us-gaap_EffectOfExchangeRateOnCash" />
    <label xml:lang="en-US" xlink:label="us-gaap_EffectOfExchangeRateOnCash_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of exchange rate changes on cash</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectOfExchangeRateOnCash" xlink:to="us-gaap_EffectOfExchangeRateOnCash_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EffectOfExchangeRateOnCash_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effect Of Exchange Rate On Cash</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net increase in cash and cash equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents Period Increase Decrease</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash and cash equivalents at the beginning of the period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents At Carrying Value Including Discontinued Operations</label>
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash and cash equivalents at the end of the period</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan" xlink:type="locator" xlink:label="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan" />
    <label xml:lang="en-US" xlink:label="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Non cash or part noncash exchange of principal and accrued interest under servier loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan" xlink:to="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_InterestAddedPrincipalBalancesLongTermDebt" xlink:type="locator" xlink:label="xoma_InterestAddedPrincipalBalancesLongTermDebt" />
    <label xml:lang="en-US" xlink:label="xoma_InterestAddedPrincipalBalancesLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Unpaid interest added to the outstanding principal amount on long-term debt.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_InterestAddedPrincipalBalancesLongTermDebt" xlink:to="xoma_InterestAddedPrincipalBalancesLongTermDebt_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock" xlink:type="locator" xlink:label="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock" />
    <label xml:lang="en-US" xlink:label="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued cost related to issuance of preferred and common stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock" xlink:to="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock" xlink:type="locator" xlink:label="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock" />
    <label xml:lang="en-US" xlink:label="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Prepaid financing cost related to issuance of common stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock" xlink:to="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_IssuanceOfCommonStockWarrant" xlink:type="locator" xlink:label="xoma_IssuanceOfCommonStockWarrant" />
    <label xml:lang="en-US" xlink:label="xoma_IssuanceOfCommonStockWarrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Issuance of common stock warrant.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IssuanceOfCommonStockWarrant" xlink:to="xoma_IssuanceOfCommonStockWarrant_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental Cash Flow Information:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InterestPaidNet" xlink:type="locator" xlink:label="us-gaap_InterestPaidNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for interest</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPaidNet" xlink:to="us-gaap_InterestPaidNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Paid Net</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:type="locator" xlink:label="us-gaap_IncomeTaxesPaidNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for taxes</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxesPaidNet" xlink:to="us-gaap_IncomeTaxesPaidNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes Paid Net</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash investing and financing activities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exchange of principal and accrued interest under the Servier loan</label>
    <label xml:lang="en-US" xlink:label="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Or Part Noncash Exchange Of Principal And Accrued Interest Under Servier Loan</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1" xlink:type="locator" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1" />
    <label xml:lang="en-US" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equipment acquired through capital lease</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1" xlink:to="us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Noncash Or Part Noncash Acquisition Fixed Assets Acquired1</label>
    <label xml:lang="en-US" xlink:label="xoma_InterestAddedPrincipalBalancesLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest added to principal balance on long-term debt</label>
    <label xml:lang="en-US" xlink:label="xoma_InterestAddedPrincipalBalancesLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Added Principal Balances Long Term Debt</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued cost related to issuance of preferred and common stock</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Cost Related To Issuance Of Preferred And Common Stock</label>
    <label xml:lang="en-US" xlink:label="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepaid financing cost related to issuance of common stock</label>
    <label xml:lang="en-US" xlink:label="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Financing Cost Related To Issuance Of Common Stock</label>
    <label xml:lang="en-US" xlink:label="xoma_IssuanceOfCommonStockWarrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock warrant under SVB loan</label>
    <label xml:lang="en-US" xlink:label="xoma_IssuanceOfCommonStockWarrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Of Common Stock Warrant</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_DescriptionOfBusinessAbstract" xlink:type="locator" xlink:label="xoma_DescriptionOfBusinessAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_DescriptionOfBusinessAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Description of business.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DescriptionOfBusinessAbstract" xlink:to="xoma_DescriptionOfBusinessAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_DescriptionOfBusinessAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Description Of Business [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NatureOfOperations" xlink:type="locator" xlink:label="us-gaap_NatureOfOperations" />
    <label xml:lang="en-US" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Description of Business</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NatureOfOperations" xlink:to="us-gaap_NatureOfOperations_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nature Of Operations</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountingPoliciesAbstract" xlink:type="locator" xlink:label="us-gaap_AccountingPoliciesAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Policies [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_AccountingPoliciesAbstract_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:type="locator" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" />
    <label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and Significant Accounting Policies</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Basis Of Presentation And Significant Accounting Policies [Text Block]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ConsolidatedFinancialStatementDetailAbstract" xlink:type="locator" xlink:label="xoma_ConsolidatedFinancialStatementDetailAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_ConsolidatedFinancialStatementDetailAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Consolidated financial statement detail.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ConsolidatedFinancialStatementDetailAbstract" xlink:to="xoma_ConsolidatedFinancialStatementDetailAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_ConsolidatedFinancialStatementDetailAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Consolidated Financial Statement Detail [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdditionalFinancialInformationDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_AdditionalFinancialInformationDisclosureTextBlock" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalFinancialInformationDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consolidated Financial Statement Detail</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalFinancialInformationDisclosureTextBlock" xlink:to="us-gaap_AdditionalFinancialInformationDisclosureTextBlock_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AdditionalFinancialInformationDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Financial Information Disclosure [Text Block]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicensingAndOtherArrangementsTextBlock" xlink:type="locator" xlink:label="xoma_LicensingAndOtherArrangementsTextBlock" />
    <label xml:lang="en-US" xlink:label="xoma_LicensingAndOtherArrangementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Licensing and other arrangements.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicensingAndOtherArrangementsTextBlock" xlink:to="xoma_LicensingAndOtherArrangementsTextBlock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_LicensingAndOtherArrangementsAbstract" xlink:type="locator" xlink:label="xoma_LicensingAndOtherArrangementsAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_LicensingAndOtherArrangementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Licensing and other arrangements.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicensingAndOtherArrangementsAbstract" xlink:to="xoma_LicensingAndOtherArrangementsAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LicensingAndOtherArrangementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Licensing And Other Arrangements [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_LicensingAndOtherArrangementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Licensing and Other Arrangements</label>
    <label xml:lang="en-US" xlink:label="xoma_LicensingAndOtherArrangementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Licensing And Other Arrangements [Text Block]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyPurchaseAgreementTextBlock" xlink:type="locator" xlink:label="xoma_RoyaltyPurchaseAgreementTextBlock" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyPurchaseAgreementTextBlock" xlink:to="xoma_RoyaltyPurchaseAgreementTextBlock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyPurchaseAgreementAbstract" xlink:type="locator" xlink:label="xoma_RoyaltyPurchaseAgreementAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyPurchaseAgreementAbstract" xlink:to="xoma_RoyaltyPurchaseAgreementAbstract_lbl" />
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MoneyMarketFundsAtCarryingValue" xlink:type="locator" xlink:label="us-gaap_MoneyMarketFundsAtCarryingValue" />
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    <loc xlink:href="xoma-20181231.xsd#xoma_LongTermEquitySecuritiesLineItems" xlink:type="locator" xlink:label="xoma_LongTermEquitySecuritiesLineItems" />
    <label xml:lang="en-US" xlink:label="xoma_LongTermEquitySecuritiesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Long term equity securities.</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MarketableSecuritiesTable" xlink:type="locator" xlink:label="us-gaap_MarketableSecuritiesTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_MarketableSecuritiesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Marketable Securities [Table]</label>
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    <loc xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <label xml:lang="en-US" xlink:label="dei_LegalEntityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal Entity</label>
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    <label xml:lang="en-US" xlink:label="xoma_RezoluteIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Rezolute, Inc.</label>
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    <loc xlink:href="xoma-20181231.xsd#xoma_EquipmentAndFurnitureGross" xlink:type="locator" xlink:label="xoma_EquipmentAndFurnitureGross" />
    <label xml:lang="en-US" xlink:label="xoma_EquipmentAndFurnitureGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Equipment and furniture gross.</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
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    <label xml:lang="en-US" xlink:label="xoma_EquipmentSoldAndDisposedDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Equipment sold and disposed during period.</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property Plant And Equipment [Line Items]</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment [Line Items]</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total proceeds from sale of equipment and disposal of certain equipment</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_GainLossOnDispositionOfAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gain (loss) on sale of equipment</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation expense</label>
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    <label xml:lang="en-US" xlink:label="xoma_AccruedRestructuringCostsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Represents the carrying value as of the balance sheet date of obligations incurred through that date and payable for restructuring activities.</label>
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    <label xml:lang="en-US" xlink:label="xoma_AccruedIncentiveCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued incentive compensation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AccruedIncentiveCompensation" xlink:to="xoma_AccruedIncentiveCompensation_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_LiabilityRelatedToSublease" xlink:type="locator" xlink:label="xoma_LiabilityRelatedToSublease" />
    <label xml:lang="en-US" xlink:label="xoma_LiabilityRelatedToSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Liability related to sublease.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LiabilityRelatedToSublease" xlink:to="xoma_LiabilityRelatedToSublease_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PayablesAndAccrualsAbstract" xlink:type="locator" xlink:label="us-gaap_PayablesAndAccrualsAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_PayablesAndAccrualsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payables And Accruals [Abstract]</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:type="locator" xlink:label="us-gaap_AccruedProfessionalFeesCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued legal and accounting fees</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedProfessionalFeesCurrent" xlink:to="us-gaap_AccruedProfessionalFeesCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Professional Fees Current</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedRestructuringCostsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued restructuring</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredRentCreditCurrent" xlink:type="locator" xlink:label="us-gaap_DeferredRentCreditCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRentCreditCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred rent</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRentCreditCurrent" xlink:to="us-gaap_DeferredRentCreditCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRentCreditCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Rent Credit Current</label>
    <label xml:lang="en-US" xlink:label="xoma_LiabilityRelatedToSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability related to sublease</label>
    <label xml:lang="en-US" xlink:label="xoma_LiabilityRelatedToSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liability Related To Sublease</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccruedSalariesCurrent" xlink:type="locator" xlink:label="us-gaap_AccruedSalariesCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedSalariesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued payroll and other benefits</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedSalariesCurrent" xlink:to="us-gaap_AccruedSalariesCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccruedSalariesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Salaries Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Accrued Liabilities Current</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicenseAgreementConsiderationReceived" xlink:type="locator" xlink:label="xoma_LicenseAgreementConsiderationReceived" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementConsiderationReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement consideration received.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicenseAgreementConsiderationReceived" xlink:to="xoma_LicenseAgreementConsiderationReceived_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ProceedsFromUpfrontPayment" xlink:type="locator" xlink:label="xoma_ProceedsFromUpfrontPayment" />
    <label xml:lang="en-US" xlink:label="xoma_ProceedsFromUpfrontPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Proceeds from upfront payment.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ProceedsFromUpfrontPayment" xlink:to="xoma_ProceedsFromUpfrontPayment_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AggregateFairValueOfCommonStock" xlink:type="locator" xlink:label="xoma_AggregateFairValueOfCommonStock" />
    <label xml:lang="en-US" xlink:label="xoma_AggregateFairValueOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate fair value of common stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AggregateFairValueOfCommonStock" xlink:to="xoma_AggregateFairValueOfCommonStock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockPremium" xlink:type="locator" xlink:label="xoma_CommonStockPremium" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock premium.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockPremium" xlink:to="xoma_CommonStockPremium_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones" xlink:type="locator" xlink:label="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones" />
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones" xlink:to="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ClosingStockPricePerShare" xlink:type="locator" xlink:label="xoma_ClosingStockPricePerShare" />
    <label xml:lang="en-US" xlink:label="xoma_ClosingStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing stock price per share.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ClosingStockPricePerShare" xlink:to="xoma_ClosingStockPricePerShare_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:type="locator" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Organization Consolidation And Presentation Of Financial Statements [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_CounterpartyNameAxis" xlink:type="locator" xlink:label="srt_CounterpartyNameAxis" />
    <label xml:lang="en-US" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</label>
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    <label xml:lang="en-US" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:type="locator" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <label xml:lang="en-US" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" />
    <label xml:lang="en-US" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repurchase Agreement Counterparty Name [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NovartisPharmaAGMember" xlink:type="locator" xlink:label="xoma_NovartisPharmaAGMember" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisPharmaAGMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Novartis Pharma AG.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NovartisPharmaAGMember" xlink:to="xoma_NovartisPharmaAGMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisPharmaAGMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Novartis Pharma AG [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisPharmaAGMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Novartis Pharma A G [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:type="locator" xlink:label="us-gaap_TypeOfArrangementAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Type of Arrangement and Non-arrangement Transactions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_TypeOfArrangementAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Arrangement [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="locator" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Arrangements and Non-arrangement Transactions</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Arrangements And Nonarrangement Transactions [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_XOMA052LicenseAgreementMember" xlink:type="locator" xlink:label="xoma_XOMA052LicenseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_XOMA052LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">XOMA-052 license agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_XOMA052LicenseAgreementMember" xlink:to="xoma_XOMA052LicenseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_XOMA052LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">XOMA-052 License Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_XOMA052LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">X O M A052 License Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_IL1TargetLicenseAgreementMember" xlink:type="locator" xlink:label="xoma_IL1TargetLicenseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_IL1TargetLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">IL1 target license agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IL1TargetLicenseAgreementMember" xlink:to="xoma_IL1TargetLicenseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_IL1TargetLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">IL-1 Target License Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_IL1TargetLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">I L1 Target License Agreement [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:type="locator" xlink:label="us-gaap_LineOfCreditFacilityAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_LineOfCreditFacilityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lender Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LineOfCreditFacilityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Line Of Credit Facility [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:type="locator" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Line of Credit Facility, Lender</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Line Of Credit Facility Lender [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LesLaboratoriesServierMember" xlink:type="locator" xlink:label="xoma_LesLaboratoriesServierMember" />
    <label xml:lang="en-US" xlink:label="xoma_LesLaboratoriesServierMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Les Laboratories Servier.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LesLaboratoriesServierMember" xlink:to="xoma_LesLaboratoriesServierMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LesLaboratoriesServierMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Les Laboratories Servier [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LesLaboratoriesServierMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Les Laboratories Servier [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <label xml:lang="en-US" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductOrServiceAxis_lbl" />
    <label xml:lang="en-US" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Product Or Service [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <label xml:lang="en-US" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_ProductsAndServicesDomain" xlink:to="srt_ProductsAndServicesDomain_lbl" />
    <label xml:lang="en-US" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Products And Services [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember" xlink:type="locator" xlink:label="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember" />
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Licenses and related materials, process and know-how and filings to regulatory authority.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember" xlink:to="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Licenses and Related Materials, Process and Know-How and Filings to Regulatory Authority [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Licenses And Related Materials Process And Know How And Filings To Regulatory Authority [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicenseAgreementMember" xlink:type="locator" xlink:label="xoma_LicenseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicenseAgreementMember" xlink:to="xoma_LicenseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NovartisInternationalPharmaceuticalLtdMember" xlink:type="locator" xlink:label="xoma_NovartisInternationalPharmaceuticalLtdMember" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisInternationalPharmaceuticalLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Novartis International Pharmaceutical Ltd.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NovartisInternationalPharmaceuticalLtdMember" xlink:to="xoma_NovartisInternationalPharmaceuticalLtdMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisInternationalPharmaceuticalLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Novartis International [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisInternationalPharmaceuticalLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Novartis International Pharmaceutical Ltd [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:type="locator" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementConsiderationReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License agreement consideration received</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementConsiderationReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Consideration Received</label>
    <label xml:lang="en-US" xlink:label="xoma_ProceedsFromUpfrontPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront payment received</label>
    <label xml:lang="en-US" xlink:label="xoma_ProceedsFromUpfrontPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Upfront Payment</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RepaymentsOfDebt" xlink:type="locator" xlink:label="us-gaap_RepaymentsOfDebt" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Repayments of debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfDebt" xlink:to="us-gaap_RepaymentsOfDebt_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repayments Of Debt</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:type="locator" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Cash received from sale of shares</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:to="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Consideration Received On Transaction</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:type="locator" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of shares sold</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:to="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Number Of Shares Issued In Transaction</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SaleOfStockPricePerShare" xlink:type="locator" xlink:label="us-gaap_SaleOfStockPricePerShare" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of stock price per share</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockPricePerShare" xlink:to="us-gaap_SaleOfStockPricePerShare_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Price Per Share</label>
    <label xml:lang="en-US" xlink:label="xoma_AggregateFairValueOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock aggregate fair value</label>
    <label xml:lang="en-US" xlink:label="xoma_AggregateFairValueOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Aggregate Fair Value Of Common Stock</label>
    <label xml:lang="en-US" xlink:label="xoma_ClosingStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock closing price</label>
    <label xml:lang="en-US" xlink:label="xoma_ClosingStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Closing Stock Price Per Share</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock premium</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Premium</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible milestone payments receivable upon achievement of development, regulatory and commercial milestones</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Eligible Milestone Payments Receivable Upon Achievement Of Development Regulatory And Commercial Milestones</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfLicenseAgreements" xlink:type="locator" xlink:label="xoma_NumberOfLicenseAgreements" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of future license agreements under optional purchase right.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NumberOfLicenseAgreements" xlink:to="xoma_NumberOfLicenseAgreements_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AgreementTerminationPriorWrittenNoticePeriod" xlink:type="locator" xlink:label="xoma_AgreementTerminationPriorWrittenNoticePeriod" />
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationPriorWrittenNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Agreement termination prior written notice period.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AgreementTerminationPriorWrittenNoticePeriod" xlink:to="xoma_AgreementTerminationPriorWrittenNoticePeriod_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfPerformanceObligations" xlink:type="locator" xlink:label="xoma_NumberOfPerformanceObligations" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfPerformanceObligations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of performance obligations.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NumberOfPerformanceObligations" xlink:to="xoma_NumberOfPerformanceObligations_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of license agreements</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of License Agreements</label>
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationPriorWrittenNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Agreement termination prior written notice period</label>
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationPriorWrittenNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Agreement Termination Prior Written Notice Period</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfPerformanceObligations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of performance obligations</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfPerformanceObligations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Performance Obligations</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:type="locator" xlink:label="us-gaap_RevenueRemainingPerformanceObligation" />
    <label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining performance obligations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRemainingPerformanceObligation" xlink:to="us-gaap_RevenueRemainingPerformanceObligation_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Remaining Performance Obligation</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicenseAgreementTransactionPrice" xlink:type="locator" xlink:label="xoma_LicenseAgreementTransactionPrice" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementTransactionPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement transaction price.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicenseAgreementTransactionPrice" xlink:to="xoma_LicenseAgreementTransactionPrice_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer" xlink:type="locator" xlink:label="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer" />
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Revenue from contract with customer recognized during the period upon satisfaction of multiple performance obligations.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer" xlink:to="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementTransactionPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License agreement transaction price</label>
    <label xml:lang="en-US" xlink:label="xoma_LicenseAgreementTransactionPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Transaction Price</label>
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recognized the entire transaction price as revenue upon completion of delivery</label>
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Recognition Multiple Performance Obligations Contract With Customer</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ContractWithCustomerLiability" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiability" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiability" xlink:to="us-gaap_ContractWithCustomerLiability_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ContractWithCustomerAssetNet" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerAssetNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerAssetNet" xlink:to="us-gaap_ContractWithCustomerAssetNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Asset Net</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognize</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:to="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Revenue Recognized</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CapitalizedContractCostNet" xlink:type="locator" xlink:label="us-gaap_CapitalizedContractCostNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_CapitalizedContractCostNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Capitalized contract costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalizedContractCostNet" xlink:to="us-gaap_CapitalizedContractCostNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CapitalizedContractCostNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Capitalized Contract Cost Net</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AgreementTerminationNoticePeriod" xlink:type="locator" xlink:label="xoma_AgreementTerminationNoticePeriod" />
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Agreement termination notice period.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AgreementTerminationNoticePeriod" xlink:to="xoma_AgreementTerminationNoticePeriod_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Agreement termination notice period</label>
    <label xml:lang="en-US" xlink:label="xoma_AgreementTerminationNoticePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Agreement Termination Notice Period</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_UpfrontPaymentRecognizedAsRevenue" xlink:type="locator" xlink:label="xoma_UpfrontPaymentRecognizedAsRevenue" />
    <label xml:lang="en-US" xlink:label="xoma_UpfrontPaymentRecognizedAsRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Upfront payment recognized as revenue.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_UpfrontPaymentRecognizedAsRevenue" xlink:to="xoma_UpfrontPaymentRecognizedAsRevenue_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_UpfrontPaymentRecognizedAsRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront payment recognized as revenue</label>
    <label xml:lang="en-US" xlink:label="xoma_UpfrontPaymentRecognizedAsRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Upfront Payment Recognized As Revenue</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MilestoneReceivedUnderCollaborationAgreement" xlink:type="locator" xlink:label="xoma_MilestoneReceivedUnderCollaborationAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_MilestoneReceivedUnderCollaborationAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to the payment percentage of milestone received under the collaboration agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MilestoneReceivedUnderCollaborationAgreement" xlink:to="xoma_MilestoneReceivedUnderCollaborationAgreement_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MilestoneReceivedUnderCollaborationAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone received under the collaboration agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_MilestoneReceivedUnderCollaborationAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Received Under Collaboration Agreement</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum" xlink:type="locator" xlink:label="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum" />
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to the maximum future development and sales milestone payments to be received by the Company.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum" xlink:to="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_UpfrontOptionPayment" xlink:type="locator" xlink:label="xoma_UpfrontOptionPayment" />
    <label xml:lang="en-US" xlink:label="xoma_UpfrontOptionPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Upfront option payment.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_UpfrontOptionPayment" xlink:to="xoma_UpfrontOptionPayment_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CollaborativeLicensingAndOtherArrangementsAbstract" xlink:type="locator" xlink:label="xoma_CollaborativeLicensingAndOtherArrangementsAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeLicensingAndOtherArrangementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaborative, licensing and other arrangements.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CollaborativeLicensingAndOtherArrangementsAbstract" xlink:to="xoma_CollaborativeLicensingAndOtherArrangementsAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeLicensingAndOtherArrangementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Licensing And Other Arrangements [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:type="locator" xlink:label="us-gaap_StatementScenarioAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementScenarioAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementScenarioAxis" xlink:to="us-gaap_StatementScenarioAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StatementScenarioAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Scenario [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:type="locator" xlink:label="us-gaap_ScenarioUnspecifiedDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScenarioUnspecifiedDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario, Unspecified</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScenarioUnspecifiedDomain" xlink:to="us-gaap_ScenarioUnspecifiedDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScenarioUnspecifiedDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Scenario Unspecified [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScenarioForecastMember" xlink:type="locator" xlink:label="us-gaap_ScenarioForecastMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScenarioForecastMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Forecast [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScenarioForecastMember" xlink:to="us-gaap_ScenarioForecastMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScenarioForecastMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Scenario Forecast [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AmendedCommonStockPurchaseAgreementMember" xlink:type="locator" xlink:label="xoma_AmendedCommonStockPurchaseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_AmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amended common stock purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AmendedCommonStockPurchaseAgreementMember" xlink:to="xoma_AmendedCommonStockPurchaseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amended Common Stock Purchase Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amended Common Stock Purchase Agreement [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:type="locator" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsidiary Sale Of Stock [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:type="locator" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Name Of Transaction [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_InitialClosingMember" xlink:type="locator" xlink:label="xoma_InitialClosingMember" />
    <label xml:lang="en-US" xlink:label="xoma_InitialClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Initial closing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_InitialClosingMember" xlink:to="xoma_InitialClosingMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_InitialClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial Closing [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_InitialClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Initial Closing [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_QualifiedFinancingMember" xlink:type="locator" xlink:label="xoma_QualifiedFinancingMember" />
    <label xml:lang="en-US" xlink:label="xoma_QualifiedFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_QualifiedFinancingMember" xlink:to="xoma_QualifiedFinancingMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_QualifiedFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Qualified Financing [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_QualifiedFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Qualified Financing [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandNineteenClosingMember" xlink:type="locator" xlink:label="xoma_TwoThousandNineteenClosingMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandNineteenClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand nineteen closing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TwoThousandNineteenClosingMember" xlink:to="xoma_TwoThousandNineteenClosingMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandNineteenClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2019 Closing [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandNineteenClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Nineteen Closing [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockPurchaseAgreementMember" xlink:type="locator" xlink:label="xoma_CommonStockPurchaseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockPurchaseAgreementMember" xlink:to="xoma_CommonStockPurchaseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock Purchase Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Purchase Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_InterimFinancingClosingMember" xlink:type="locator" xlink:label="xoma_InterimFinancingClosingMember" />
    <label xml:lang="en-US" xlink:label="xoma_InterimFinancingClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Interim financing closing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_InterimFinancingClosingMember" xlink:to="xoma_InterimFinancingClosingMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_InterimFinancingClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interim Financing Closing [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_InterimFinancingClosingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interim Financing Closing [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember" xlink:type="locator" xlink:label="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amended license agreement and amended common stock purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember" xlink:to="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amended License Agreement and Amended Common Stock Purchase Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amended License Agreement And Amended Common Stock Purchase Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember" xlink:type="locator" xlink:label="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember" />
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Licenses and related materials, product data/filing, process and know-how.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember" xlink:to="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Licenses and Related Materials, Product Data/Filing, Process and Know-how [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Licenses And Related Materials Product Data Or Filing Process And Know How [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Future milestone payments, maximum</label>
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement Contingent Consideration Potential Cash Payment Maximum</label>
    <label xml:lang="en-US" xlink:label="xoma_UpfrontOptionPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront option fee</label>
    <label xml:lang="en-US" xlink:label="xoma_UpfrontOptionPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Upfront Option Payment</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_EligibleToReceiveInCash" xlink:type="locator" xlink:label="xoma_EligibleToReceiveInCash" />
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInCash_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Eligible to receive in cash.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EligibleToReceiveInCash" xlink:to="xoma_EligibleToReceiveInCash_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities" xlink:type="locator" xlink:label="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities" />
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Eligible to receive common stock related to financing activities.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities" xlink:to="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_GrossProceedsFromQualifiedFinancing" xlink:type="locator" xlink:label="xoma_GrossProceedsFromQualifiedFinancing" />
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Gross proceeds from qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_GrossProceedsFromQualifiedFinancing" xlink:to="xoma_GrossProceedsFromQualifiedFinancing_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AdditionalCommonStockReceiveForQualifiedFinancing" xlink:type="locator" xlink:label="xoma_AdditionalCommonStockReceiveForQualifiedFinancing" />
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCommonStockReceiveForQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional common stock receive for qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AdditionalCommonStockReceiveForQualifiedFinancing" xlink:to="xoma_AdditionalCommonStockReceiveForQualifiedFinancing_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockThresholdTradingDays" xlink:type="locator" xlink:label="xoma_CommonStockThresholdTradingDays" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockThresholdTradingDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock threshold trading days.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockThresholdTradingDays" xlink:to="xoma_CommonStockThresholdTradingDays_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement" xlink:type="locator" xlink:label="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Eligible to receive in order to maintain license agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement" xlink:to="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInCash_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible to receive in cash</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInCash_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Eligible To Receive In Cash</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible to receive common stock, financing activities</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Eligible To Receive Common Stock Related To Financing Activities</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross proceeds from qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Gross Proceeds From Qualified Financing</label>
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCommonStockReceiveForQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional common stock receive for qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCommonStockReceiveForQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Common Stock Receive For Qualified Financing</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockThresholdTradingDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, trading period</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockThresholdTradingDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Threshold Trading Days</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible to receive, in order to maintain license agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Eligible To Receive In Order To Maintain License Agreement</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfAggregateSharesHeldForFutureIssuance" xlink:type="locator" xlink:label="xoma_PercentageOfAggregateSharesHeldForFutureIssuance" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAggregateSharesHeldForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of aggregate shares held for future issuance.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfAggregateSharesHeldForFutureIssuance" xlink:to="xoma_PercentageOfAggregateSharesHeldForFutureIssuance_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockPurchaseAgreementDescription" xlink:type="locator" xlink:label="xoma_CommonStockPurchaseAgreementDescription" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock purchase agreement description.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockPurchaseAgreementDescription" xlink:to="xoma_CommonStockPurchaseAgreementDescription_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:type="locator" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares of common stock held for future issuance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Capital Shares Reserved For Future Issuance</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock purchase agreement description</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockPurchaseAgreementDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Purchase Agreement Description</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAggregateSharesHeldForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of aggregate shares held for future issuance</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAggregateSharesHeldForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Aggregate Shares Held For Future Issuance</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockValueReceivable" xlink:type="locator" xlink:label="xoma_CommonStockValueReceivable" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockValueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock value receivable.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockValueReceivable" xlink:to="xoma_CommonStockValueReceivable_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockSharesReceivable" xlink:type="locator" xlink:label="xoma_CommonStockSharesReceivable" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockSharesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock shares receivable.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockSharesReceivable" xlink:to="xoma_CommonStockSharesReceivable_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockValueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock value receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockValueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Value Receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockSharesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock shares receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockSharesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Receivable</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SharesReceived" xlink:type="locator" xlink:label="xoma_SharesReceived" />
    <label xml:lang="en-US" xlink:label="xoma_SharesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Shares received.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SharesReceived" xlink:to="xoma_SharesReceived_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CashReceived" xlink:type="locator" xlink:label="xoma_CashReceived" />
    <label xml:lang="en-US" xlink:label="xoma_CashReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash received.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CashReceived" xlink:to="xoma_CashReceived_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SharesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock received</label>
    <label xml:lang="en-US" xlink:label="xoma_SharesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Received</label>
    <label xml:lang="en-US" xlink:label="xoma_CashReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash received</label>
    <label xml:lang="en-US" xlink:label="xoma_CashReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Received</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Contract revenue</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ReimbursableTechnologyTransferExpensesReceived" xlink:type="locator" xlink:label="xoma_ReimbursableTechnologyTransferExpensesReceived" />
    <label xml:lang="en-US" xlink:label="xoma_ReimbursableTechnologyTransferExpensesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Reimbursable technology transfer expenses received.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ReimbursableTechnologyTransferExpensesReceived" xlink:to="xoma_ReimbursableTechnologyTransferExpensesReceived_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Gross proceeds from debt financing activity</label>
    <label xml:lang="en-US" xlink:label="xoma_ReimbursableTechnologyTransferExpensesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reimbursable technology transfer expenses received</label>
    <label xml:lang="en-US" xlink:label="xoma_ReimbursableTechnologyTransferExpensesReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Reimbursable Technology Transfer Expenses Received</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment" xlink:type="locator" xlink:label="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment" />
    <label xml:lang="en-US" xlink:label="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Upfront consideration to incremental discount for future payment.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment" xlink:to="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront consideration to incremental discount for future payment</label>
    <label xml:lang="en-US" xlink:label="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Upfront Consideration To Incremental Discount For Future Payment</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SharesReceivedValue" xlink:type="locator" xlink:label="xoma_SharesReceivedValue" />
    <label xml:lang="en-US" xlink:label="xoma_SharesReceivedValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Shares received value.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SharesReceivedValue" xlink:to="xoma_SharesReceivedValue_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" xlink:type="locator" xlink:label="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" />
    <label xml:lang="en-US" xlink:label="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer, liability multiple deliverable arrangements determination of selling price amount.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" xlink:to="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SharesReceivedValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Value of common stock received</label>
    <label xml:lang="en-US" xlink:label="xoma_SharesReceivedValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Received Value</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recognized the entire transaction price as revenue upon completion of delivery</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Multiple Deliverable Arrangements Determination Of Selling Price Amount</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MaximumRevenueFromContract" xlink:type="locator" xlink:label="xoma_MaximumRevenueFromContract" />
    <label xml:lang="en-US" xlink:label="xoma_MaximumRevenueFromContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum revenue from contract.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MaximumRevenueFromContract" xlink:to="xoma_MaximumRevenueFromContract_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ContractualTerm" xlink:type="locator" xlink:label="xoma_ContractualTerm" />
    <label xml:lang="en-US" xlink:label="xoma_ContractualTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractual term of collaborative, licensing and other arrangements, in &apos;PnYnMnDTnHnMnS&apos; format, for example, &apos;P1Y5M13D&apos; represents the reported fact of one year, five months, and thirteen days.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContractualTerm" xlink:to="xoma_ContractualTerm_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ContractsRevenueWroteOff" xlink:type="locator" xlink:label="xoma_ContractsRevenueWroteOff" />
    <label xml:lang="en-US" xlink:label="xoma_ContractsRevenueWroteOff_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contracts revenue wrote off.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContractsRevenueWroteOff" xlink:to="xoma_ContractsRevenueWroteOff_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DeferredRevenueArrangementNameOfParty2Member" xlink:type="locator" xlink:label="xoma_DeferredRevenueArrangementNameOfParty2Member" />
    <label xml:lang="en-US" xlink:label="xoma_DeferredRevenueArrangementNameOfParty2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Describes the name of the party related to a deferred revenue arrangement. The party named is the other party that participates in a deferred revenue transaction.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DeferredRevenueArrangementNameOfParty2Member" xlink:to="xoma_DeferredRevenueArrangementNameOfParty2Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_DeferredRevenueArrangementNameOfParty2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">National Institute of Allergy and Infectious Diseases "NIAID" [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_DeferredRevenueArrangementNameOfParty2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue Arrangement Name Of Party2 [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member" xlink:type="locator" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member" />
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Category of deferred revenue arrangement wherein certain rights are granted under a license agreement with a governmental agency.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member" xlink:to="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Arrangement with Governmental Agency 2 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nonsoftware License Arrangement With Governmental Agency2 [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member" xlink:type="locator" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member" />
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Category of deferred revenue arrangement wherein certain rights are granted under a license agreement with a governmental agency.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member" xlink:to="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Arrangement with Governmental Agency 3 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nonsoftware License Arrangement With Governmental Agency3 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MaximumRevenueFromContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total contract amount awarded</label>
    <label xml:lang="en-US" xlink:label="xoma_MaximumRevenueFromContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Revenue From Contract</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractualTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contractual term</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractualTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contractual Term</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsReceivableNet" xlink:type="locator" xlink:label="us-gaap_AccountsReceivableNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts receivable</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsReceivableNet" xlink:to="us-gaap_AccountsReceivableNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable Net</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Deferred revenue balance classified as contract liability due to government adjustment</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractsRevenueWroteOff_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contracts revenue wrote off</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractsRevenueWroteOff_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contracts Revenue Wrote Off</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones" xlink:type="locator" xlink:label="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones" />
    <label xml:lang="en-US" xlink:label="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Eligible potential additional payments receivable upon achievement of specified future net sales milestones.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones" xlink:to="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfRoyaltyInterestAcquisitionAgreements" xlink:type="locator" xlink:label="xoma_NumberOfRoyaltyInterestAcquisitionAgreements" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfRoyaltyInterestAcquisitionAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of royalty interest acquisition agreements.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NumberOfRoyaltyInterestAcquisitionAgreements" xlink:to="xoma_NumberOfRoyaltyInterestAcquisitionAgreements_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember" xlink:type="locator" xlink:label="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember" />
    <label xml:lang="en-US" xlink:label="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Health care royalty partners II L.P.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember" xlink:to="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">HCRP [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Health Care Royalty Partners Two Limited Partners [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FirstRoyaltyInterestAcquisitionAgreementMember" xlink:type="locator" xlink:label="xoma_FirstRoyaltyInterestAcquisitionAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_FirstRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">First Royalty Interest Acquisition Agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FirstRoyaltyInterestAcquisitionAgreementMember" xlink:to="xoma_FirstRoyaltyInterestAcquisitionAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_FirstRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">First Acquisition Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_FirstRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">First Royalty Interest Acquisition Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SecondRoyaltyInterestAcquisitionAgreementMember" xlink:type="locator" xlink:label="xoma_SecondRoyaltyInterestAcquisitionAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_SecondRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Second Royalty Interest Acquisition Agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SecondRoyaltyInterestAcquisitionAgreementMember" xlink:to="xoma_SecondRoyaltyInterestAcquisitionAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SecondRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Second Acquisition Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SecondRoyaltyInterestAcquisitionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Second Royalty Interest Acquisition Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfRoyaltyInterestAcquisitionAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of royalty Interest acquisition agreements</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfRoyaltyInterestAcquisitionAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Royalty Interest Acquisition Agreements</label>
    <label xml:lang="en-US" xlink:label="xoma_ProceedsFromUpfrontPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Upfront cash payment received</label>
    <label xml:lang="en-US" xlink:label="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible potential additional payments receivable upon achievement of specified net sales milestones in future years</label>
    <label xml:lang="en-US" xlink:label="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Eligible Potential Additional Payments Receivable Upon Achievement Of Specified Future Net Sales Milestones</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredRevenue" xlink:type="locator" xlink:label="us-gaap_DeferredRevenue" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Unearned revenue recognized under units-of-revenue method</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenue" xlink:to="us-gaap_DeferredRevenue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RevenueRecognizedUnderUnitsOfRevenueMethod" xlink:type="locator" xlink:label="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod" />
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount recognized from the amortization of upfront payment resulting from the sale of royalties.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod" xlink:to="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognized under units-of-revenue method</label>
    <label xml:lang="en-US" xlink:label="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Recognized Under Units Of Revenue Method</label>
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Unearned revenue recognized under units-of-revenue method</label>
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredRevenueNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Unearned revenue recognized under units-of-revenue method &#8211; long-term</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts" xlink:type="locator" xlink:label="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts" />
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Purchased percentage of royalties on net sales of products.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts" xlink:to="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PurchasedPercentageOfMilestones" xlink:type="locator" xlink:label="xoma_PurchasedPercentageOfMilestones" />
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Purchased percentage of milestones.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PurchasedPercentageOfMilestones" xlink:to="xoma_PurchasedPercentageOfMilestones_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased" xlink:type="locator" xlink:label="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of licensed products related to milestones and royalties purchased.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased" xlink:to="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones" xlink:type="locator" xlink:label="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones" />
    <label xml:lang="en-US" xlink:label="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Purchased eligible milestone payments receivable upon achievement of potential development regulatory and commercial milestones.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones" xlink:to="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyPurchaseAgreementLineItems" xlink:type="locator" xlink:label="xoma_RoyaltyPurchaseAgreementLineItems" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyPurchaseAgreementLineItems" xlink:to="xoma_RoyaltyPurchaseAgreementLineItems_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyPurchaseAgreementTable" xlink:type="locator" xlink:label="xoma_RoyaltyPurchaseAgreementTable" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyPurchaseAgreementTable" xlink:to="xoma_RoyaltyPurchaseAgreementTable_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Purchase Agreement [Table]</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement [Table]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyPurchaseAgreementMember" xlink:type="locator" xlink:label="xoma_RoyaltyPurchaseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyPurchaseAgreementMember" xlink:to="xoma_RoyaltyPurchaseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Purchase Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AgenusIncMember" xlink:type="locator" xlink:label="xoma_AgenusIncMember" />
    <label xml:lang="en-US" xlink:label="xoma_AgenusIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Agenus Inc.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AgenusIncMember" xlink:to="xoma_AgenusIncMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AgenusIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Agenus [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AgenusIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Agenus Inc [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember" xlink:type="locator" xlink:label="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember" />
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Right to receive low-single to mid-teen digit royalties.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember" xlink:to="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Right to Receive Low-Single Mid-Teen Royalties [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Right To Receive Low Single To Mid Teen Digit Royalties [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RightToReceiveLowSingleDigitRoyaltiesMember" xlink:type="locator" xlink:label="xoma_RightToReceiveLowSingleDigitRoyaltiesMember" />
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Right to receive low single digit royalties.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RightToReceiveLowSingleDigitRoyaltiesMember" xlink:to="xoma_RightToReceiveLowSingleDigitRoyaltiesMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Right to Receive Low Single Digit Royalties [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_RightToReceiveLowSingleDigitRoyaltiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Right To Receive Low Single Digit Royalties [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_IncyteEuropeSarlMember" xlink:type="locator" xlink:label="xoma_IncyteEuropeSarlMember" />
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Incyte Europe Sarl.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IncyteEuropeSarlMember" xlink:to="xoma_IncyteEuropeSarlMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Incyte [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Incyte Europe Sarl [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MerckSharpAndDohmeCorporationMember" xlink:type="locator" xlink:label="xoma_MerckSharpAndDohmeCorporationMember" />
    <label xml:lang="en-US" xlink:label="xoma_MerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Merck Sharp &amp; Dohme Corporation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MerckSharpAndDohmeCorporationMember" xlink:to="xoma_MerckSharpAndDohmeCorporationMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Merck [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Merck Sharp And Dohme Corporation [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember" xlink:type="locator" xlink:label="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember" />
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Incyte Europe Sarl and Merck Sharp and Dohme Corporation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember" xlink:to="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Incyte and Merck [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Incyte Europe Sarl And Merck Sharp And Dohme Corporation [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SiliconValleyBankMember" xlink:type="locator" xlink:label="xoma_SiliconValleyBankMember" />
    <label xml:lang="en-US" xlink:label="xoma_SiliconValleyBankMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Silicon Valley Bank.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SiliconValleyBankMember" xlink:to="xoma_SiliconValleyBankMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SiliconValleyBankMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Silicon Valley Bank [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SiliconValleyBankMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Silicon Valley Bank [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Purchase Agreement [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyPurchaseAgreementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Purchased percentage of royalties on net sales of products</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Purchased Percentage Of Royalties On Net Sales Of Products</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Purchased percentage of milestones</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedPercentageOfMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Purchased Percentage Of Milestones</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of licensed products related to milestone and royalties</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Licensed Products Related To Milestones And Royalties Purchased</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Purchased eligible milestone payments receivable upon achievement of potential development, regulatory and commercial milestones</label>
    <label xml:lang="en-US" xlink:label="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Purchased Eligible Milestone Payments Receivable Upon Achievement Of Potential Development Regulatory And Commercial Milestones</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PaymentsToAcquireMilestonesAndRoyalties" xlink:type="locator" xlink:label="xoma_PaymentsToAcquireMilestonesAndRoyalties" />
    <label xml:lang="en-US" xlink:label="xoma_PaymentsToAcquireMilestonesAndRoyalties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Payments to acquire milestones and royalties.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PaymentsToAcquireMilestonesAndRoyalties" xlink:to="xoma_PaymentsToAcquireMilestonesAndRoyalties_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_LoanBorrowed" xlink:type="locator" xlink:label="xoma_LoanBorrowed" />
    <label xml:lang="en-US" xlink:label="xoma_LoanBorrowed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Loan borrowed.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LoanBorrowed" xlink:to="xoma_LoanBorrowed_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_PaymentsToAcquireMilestonesAndRoyalties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payments to acquire milestones and royalties</label>
    <label xml:lang="en-US" xlink:label="xoma_PaymentsToAcquireMilestonesAndRoyalties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Milestones And Royalties</label>
    <label xml:lang="en-US" xlink:label="xoma_LoanBorrowed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan borrowed</label>
    <label xml:lang="en-US" xlink:label="xoma_LoanBorrowed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Loan Borrowed</label>
    <label xml:lang="en-US" xlink:label="xoma_LongTermRoyaltyReceivableNonCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Long-term royalty receivables</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discount for Lack of Marketability [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:to="us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Discount For Lack Of Marketability [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MeasurementInputLiquidityOfSharesMember" xlink:type="locator" xlink:label="xoma_MeasurementInputLiquidityOfSharesMember" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidityOfSharesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input, liquidity of shares.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MeasurementInputLiquidityOfSharesMember" xlink:to="xoma_MeasurementInputLiquidityOfSharesMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidityOfSharesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liquidity of Shares [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidityOfSharesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Liquidity Of Shares [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MeasurementInputLiquidationMember" xlink:type="locator" xlink:label="xoma_MeasurementInputLiquidationMember" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input, liquidation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MeasurementInputLiquidationMember" xlink:to="xoma_MeasurementInputLiquidationMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liquidation [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputLiquidationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Liquidation [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MeasurementInputNearTermSaleMember" xlink:type="locator" xlink:label="xoma_MeasurementInputNearTermSaleMember" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermSaleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input, near-term sale.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MeasurementInputNearTermSaleMember" xlink:to="xoma_MeasurementInputNearTermSaleMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermSaleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Near-term Sale [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermSaleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Near Term Sale [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_MeasurementInputNearTermFinancingMember" xlink:type="locator" xlink:label="xoma_MeasurementInputNearTermFinancingMember" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input near-term financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MeasurementInputNearTermFinancingMember" xlink:to="xoma_MeasurementInputNearTermFinancingMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Near-term Financing [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_MeasurementInputNearTermFinancingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Near Term Financing [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquitySecuritiesFvNiMeasurementInput" xlink:type="locator" xlink:label="us-gaap_EquitySecuritiesFvNiMeasurementInput" />
    <label xml:lang="en-US" xlink:label="us-gaap_EquitySecuritiesFvNiMeasurementInput_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation assumptions, measurement input</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquitySecuritiesFvNiMeasurementInput" xlink:to="us-gaap_EquitySecuritiesFvNiMeasurementInput_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EquitySecuritiesFvNiMeasurementInput_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Securities Fv Ni Measurement Input</label>
    <label xml:lang="en-US" xlink:label="xoma_EquitySecuritiesFvNiTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation assumptions, measurement input term</label>
    <label xml:lang="en-US" xlink:label="xoma_EquitySecuritiesFvNiTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Securities Fv Ni Term</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:type="locator" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value By Balance Sheet Grouping [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByBalanceSheetGroupingTable" xlink:to="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Balance Sheet Grouping [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Basis</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_FairValueByMeasurementBasisAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Measurement Basis [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Disclosure Item Amounts [Default]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Portion At Fair Value Fair Value Disclosure [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:type="locator" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurement</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosureItemAmountsDomain" xlink:to="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosure Item Amounts [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Carrying Amount [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Carrying Reported Amount Fair Value Disclosure [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentNameDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="us-gaap_DebtInstrumentNameDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Name [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NovartisNoteMember" xlink:type="locator" xlink:label="xoma_NovartisNoteMember" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">A written promise to pay a note to Novartis.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NovartisNoteMember" xlink:to="xoma_NovartisNoteMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Novartis Note [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Novartis Note [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SiliconValleyBankMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">SVB Loan [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimate Of Fair Value Fair Value Disclosure [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongTermDebtFairValue" xlink:type="locator" xlink:label="us-gaap_LongTermDebtFairValue" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtFairValue" xlink:to="us-gaap_LongTermDebtFairValue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Fair Value</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ContingentPayment" xlink:type="locator" xlink:label="xoma_ContingentPayment" />
    <label xml:lang="en-US" xlink:label="xoma_ContingentPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The amount of contingent payments the company is entitled to receive related to sole performance of counterparty under the agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContingentPayment" xlink:to="xoma_ContingentPayment_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive" xlink:type="locator" xlink:label="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive" />
    <label xml:lang="en-US" xlink:label="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sales of business number of common stock shares eligible to receive.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive" xlink:to="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RoyaltyReceivablePercentageOnNetSales" xlink:type="locator" xlink:label="xoma_RoyaltyReceivablePercentageOnNetSales" />
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyReceivablePercentageOnNetSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty receivable percentage on net sales.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RoyaltyReceivablePercentageOnNetSales" xlink:to="xoma_RoyaltyReceivablePercentageOnNetSales_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:type="locator" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Disposal Group Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:type="locator" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Disposal Group Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Groups Including Discontinued Operations Name [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_BiodefenseBusinessMember" xlink:type="locator" xlink:label="xoma_BiodefenseBusinessMember" />
    <label xml:lang="en-US" xlink:label="xoma_BiodefenseBusinessMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Biodefense business.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_BiodefenseBusinessMember" xlink:to="xoma_BiodefenseBusinessMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_BiodefenseBusinessMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Biodefense Business [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_BiodefenseBusinessMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Biodefense Business [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Range</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeAxis" xlink:to="srt_RangeAxis_lbl" />
    <label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Range</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeMember" xlink:to="srt_RangeMember_lbl" />
    <label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MaximumMember" xlink:to="srt_MaximumMember_lbl" />
    <label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MinimumMember" xlink:to="srt_MinimumMember_lbl" />
    <label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember" xlink:type="locator" xlink:label="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Asset purchase agreement and Ology Bioservices license agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember" xlink:to="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Purchase Agreement and Ology Bioservices License Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Asset Purchase Agreement And Ology Bioservices License Agreement [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:type="locator" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_ContingentPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash payments from Ology Bioservices</label>
    <label xml:lang="en-US" xlink:label="xoma_ContingentPayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payment</label>
    <label xml:lang="en-US" xlink:label="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sales of business, number of common stock shares eligible to receive</label>
    <label xml:lang="en-US" xlink:label="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sales Of Business Number Of Common Stock Shares Eligible To Receive</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyReceivablePercentageOnNetSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalties receivable percentage on net sales</label>
    <label xml:lang="en-US" xlink:label="xoma_RoyaltyReceivablePercentageOnNetSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Receivable Percentage On Net Sales</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement" xlink:type="locator" xlink:label="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cancellation of issuance of common stock under purchase agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement" xlink:to="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives" xlink:type="locator" xlink:label="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives" />
    <label xml:lang="en-US" xlink:label="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payment upon achieving certain specified future operating objectives.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives" xlink:to="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_MilestonePaymentEarned" xlink:type="locator" xlink:label="xoma_MilestonePaymentEarned" />
    <label xml:lang="en-US" xlink:label="xoma_MilestonePaymentEarned_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payment earned.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MilestonePaymentEarned" xlink:to="xoma_MilestonePaymentEarned_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AmountReceivedFromSaleOfDiscontinuedOperation" xlink:type="locator" xlink:label="xoma_AmountReceivedFromSaleOfDiscontinuedOperation" />
    <label xml:lang="en-US" xlink:label="xoma_AmountReceivedFromSaleOfDiscontinuedOperation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount received from sale of discontinued operation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AmountReceivedFromSaleOfDiscontinuedOperation" xlink:to="xoma_AmountReceivedFromSaleOfDiscontinuedOperation_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares removed from obligation to issue of common stock</label>
    <label xml:lang="en-US" xlink:label="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cancellation Of Issuance Of Common Stock Under Purchase Agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent upon achieving certain specified future operating objectives</label>
    <label xml:lang="en-US" xlink:label="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payment Upon Achieving Certain Specified Future Operating Objectives</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration" xlink:type="locator" xlink:label="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration" />
    <label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amount entitled to receive</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration" xlink:to="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Group Including Discontinued Operation Consideration</label>
    <label xml:lang="en-US" xlink:label="xoma_MilestonePaymentEarned_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payment earned</label>
    <label xml:lang="en-US" xlink:label="xoma_MilestonePaymentEarned_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payment Earned</label>
    <label xml:lang="en-US" xlink:label="xoma_AmountReceivedFromSaleOfDiscontinuedOperation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amount received from sale of discontinued operation</label>
    <label xml:lang="en-US" xlink:label="xoma_AmountReceivedFromSaleOfDiscontinuedOperation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amount Received From Sale Of Discontinued Operation</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated" xlink:type="locator" xlink:label="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated" />
    <label xml:lang="en-US" xlink:label="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Restructuring and related cost number of employees terminated.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated" xlink:to="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Restructuring And Related Costs [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:to="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Restructuring And Related Costs [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringPlanAxis" xlink:type="locator" xlink:label="us-gaap_RestructuringPlanAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringPlanAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring Plan</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringPlanAxis" xlink:to="us-gaap_RestructuringPlanAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringPlanAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Plan [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringPlanDomain" xlink:type="locator" xlink:label="us-gaap_RestructuringPlanDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringPlanDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring Plan</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringPlanDomain" xlink:to="us-gaap_RestructuringPlanDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringPlanDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Plan [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandSixteenRestructuringMember" xlink:type="locator" xlink:label="xoma_TwoThousandSixteenRestructuringMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand sixteen restructuring.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TwoThousandSixteenRestructuringMember" xlink:to="xoma_TwoThousandSixteenRestructuringMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2016 Restructuring [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Sixteen Restructuring [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandSeventeenRestructuringMember" xlink:type="locator" xlink:label="xoma_TwoThousandSeventeenRestructuringMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand seventeen restructuring.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TwoThousandSeventeenRestructuringMember" xlink:to="xoma_TwoThousandSeventeenRestructuringMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2017 Restructuring [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Seventeen Restructuring [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember" xlink:type="locator" xlink:label="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand seventeen and two thousand sixteen restructuring.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember" xlink:to="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2017 and 2016 Restructuring [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Seventeen And Two Thousand Sixteen Restructuring [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringCostAndReserveAxis" xlink:type="locator" xlink:label="us-gaap_RestructuringCostAndReserveAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringCostAndReserveAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringCostAndReserveAxis" xlink:to="us-gaap_RestructuringCostAndReserveAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringCostAndReserveAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Cost And Reserve [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TypeOfRestructuringDomain" xlink:type="locator" xlink:label="us-gaap_TypeOfRestructuringDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_TypeOfRestructuringDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Type of Restructuring</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfRestructuringDomain" xlink:to="us-gaap_TypeOfRestructuringDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_TypeOfRestructuringDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Restructuring [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EmployeeSeveranceMember" xlink:type="locator" xlink:label="us-gaap_EmployeeSeveranceMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_EmployeeSeveranceMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Severance, Other Termination Benefits and Outplacement Services [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeSeveranceMember" xlink:to="us-gaap_EmployeeSeveranceMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EmployeeSeveranceMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Severance [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LeaseRelatedCostsMember" xlink:type="locator" xlink:label="xoma_LeaseRelatedCostsMember" />
    <label xml:lang="en-US" xlink:label="xoma_LeaseRelatedCostsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lease-related costs.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LeaseRelatedCostsMember" xlink:to="xoma_LeaseRelatedCostsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LeaseRelatedCostsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease-related Costs [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LeaseRelatedCostsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Related Costs [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Balance Sheet Location [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_BalanceSheetLocationDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Balance Sheet Location [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AccruedAndOtherLiabilitiesMember" xlink:type="locator" xlink:label="xoma_AccruedAndOtherLiabilitiesMember" />
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued and other liabilities.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AccruedAndOtherLiabilitiesMember" xlink:to="xoma_AccruedAndOtherLiabilitiesMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued and Other Liabilities [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AccruedAndOtherLiabilitiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued And Other Liabilities [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:type="locator" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Liabilities Non-current [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherNoncurrentLiabilitiesMember" xlink:to="us-gaap_OtherNoncurrentLiabilitiesMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Noncurrent Liabilities [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringCostAndReserveLineItems" xlink:type="locator" xlink:label="us-gaap_RestructuringCostAndReserveLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringCostAndReserveLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring Cost And Reserve [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringCostAndReserveLineItems" xlink:to="us-gaap_RestructuringCostAndReserveLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringCostAndReserveLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Cost And Reserve [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of employees terminated</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring And Related Cost Number Of Employees Terminated</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringChargesCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring charges (credit)</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringChargesCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Charges Credits</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_RestructuringReversalOfDeferredRentLiabilities" xlink:type="locator" xlink:label="xoma_RestructuringReversalOfDeferredRentLiabilities" />
    <label xml:lang="en-US" xlink:label="xoma_RestructuringReversalOfDeferredRentLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Restructuring reversal of deferred rent liabilities.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RestructuringReversalOfDeferredRentLiabilities" xlink:to="xoma_RestructuringReversalOfDeferredRentLiabilities_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesNumberOfSubtenants" xlink:type="locator" xlink:label="xoma_OperatingLeasesNumberOfSubtenants" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfSubtenants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases number of subtenants.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesNumberOfSubtenants" xlink:to="xoma_OperatingLeasesNumberOfSubtenants_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfSubtenants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, number of subtenants</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfSubtenants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Number Of Subtenants</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringReserve" xlink:type="locator" xlink:label="us-gaap_RestructuringReserve" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserve_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring liability</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringReserve" xlink:to="us-gaap_RestructuringReserve_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserve_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Reserve</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringReversalOfDeferredRentLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reversal of deferred rent liability</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringReversalOfDeferredRentLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Reversal Of Deferred Rent Liabilities</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringReserveCurrent" xlink:type="locator" xlink:label="us-gaap_RestructuringReserveCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserveCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Combined lease-related liabilities, current portion</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringReserveCurrent" xlink:to="us-gaap_RestructuringReserveCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserveCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Reserve Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringReserveNoncurrent" xlink:type="locator" xlink:label="us-gaap_RestructuringReserveNoncurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserveNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Combined lease-related liabilities, non-current portion</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringReserveNoncurrent" xlink:to="us-gaap_RestructuringReserveNoncurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringReserveNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Reserve Noncurrent</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_DebtInstrumentMaximumBorrowingCapacity" xlink:type="locator" xlink:label="xoma_DebtInstrumentMaximumBorrowingCapacity" />
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaximumBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The maximum borrowing capacity for a debt instrument under the loan agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DebtInstrumentMaximumBorrowingCapacity" xlink:to="xoma_DebtInstrumentMaximumBorrowingCapacity_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_IncreaseInDebtInstrumentBorrowingCapacity" xlink:type="locator" xlink:label="xoma_IncreaseInDebtInstrumentBorrowingCapacity" />
    <label xml:lang="en-US" xlink:label="xoma_IncreaseInDebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Increase in debt instrument borrowing capacity.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IncreaseInDebtInstrumentBorrowingCapacity" xlink:to="xoma_IncreaseInDebtInstrumentBorrowingCapacity_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EarlierEffectiveDateOfTermLoan" xlink:type="locator" xlink:label="xoma_EarlierEffectiveDateOfTermLoan" />
    <label xml:lang="en-US" xlink:label="xoma_EarlierEffectiveDateOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Earlier effective date of term loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EarlierEffectiveDateOfTermLoan" xlink:to="xoma_EarlierEffectiveDateOfTermLoan_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_EffectiveDateOfTermLoanExtended" xlink:type="locator" xlink:label="xoma_EffectiveDateOfTermLoanExtended" />
    <label xml:lang="en-US" xlink:label="xoma_EffectiveDateOfTermLoanExtended_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Effective date of term loan extended.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_EffectiveDateOfTermLoanExtended" xlink:to="xoma_EffectiveDateOfTermLoanExtended_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments" xlink:type="locator" xlink:label="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments" />
    <label xml:lang="en-US" xlink:label="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Gross cash proceeds received from milestone and licensing payments.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments" xlink:to="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Table]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LoanAndSecurityAgreementMember" xlink:type="locator" xlink:label="xoma_LoanAndSecurityAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Loan and Security Agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LoanAndSecurityAgreementMember" xlink:to="xoma_LoanAndSecurityAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan and Security Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Loan And Security Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TermLoanMember" xlink:type="locator" xlink:label="xoma_TermLoanMember" />
    <label xml:lang="en-US" xlink:label="xoma_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Term loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TermLoanMember" xlink:to="xoma_TermLoanMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Term Loan [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableRateAxis" xlink:type="locator" xlink:label="us-gaap_VariableRateAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableRateDomain" xlink:type="locator" xlink:label="us-gaap_VariableRateDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_VariableRateDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PrimeRateMember" xlink:type="locator" xlink:label="us-gaap_PrimeRateMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_PrimeRateMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prime Rate [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrimeRateMember" xlink:to="us-gaap_PrimeRateMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PrimeRateMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Prime Rate [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NovartisMember" xlink:type="locator" xlink:label="xoma_NovartisMember" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Novartis.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NovartisMember" xlink:to="xoma_NovartisMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Novartis [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Novartis [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Redemption, Period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:to="us-gaap_DebtInstrumentRedemptionPeriodAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Redemption Period [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Redemption, Period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:to="us-gaap_DebtInstrumentRedemptionPeriodDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Redemption Period [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FirstAnniversaryMember" xlink:type="locator" xlink:label="xoma_FirstAnniversaryMember" />
    <label xml:lang="en-US" xlink:label="xoma_FirstAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">First anniversary.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FirstAnniversaryMember" xlink:to="xoma_FirstAnniversaryMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_FirstAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">First Anniversary [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_FirstAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">First Anniversary [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SecondAnniversaryMember" xlink:type="locator" xlink:label="xoma_SecondAnniversaryMember" />
    <label xml:lang="en-US" xlink:label="xoma_SecondAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Second anniversary.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SecondAnniversaryMember" xlink:to="xoma_SecondAnniversaryMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SecondAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Second Anniversary [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SecondAnniversaryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Second Anniversary [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_WarrantMember" xlink:type="locator" xlink:label="us-gaap_WarrantMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_WarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants for Common Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantMember" xlink:to="us-gaap_WarrantMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_WarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrant [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaximumBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum borrowing capacity under loan agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaximumBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Maximum Borrowing Capacity</label>
    <label xml:lang="en-US" xlink:label="xoma_IncreaseInDebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase borrowing capacity under loan agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_IncreaseInDebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase In Debt Instrument Borrowing Capacity</label>
    <label xml:lang="en-US" xlink:label="xoma_EarlierEffectiveDateOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earlier effecitve date of term loan</label>
    <label xml:lang="en-US" xlink:label="xoma_EarlierEffectiveDateOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earlier Effective Date Of Term Loan</label>
    <label xml:lang="en-US" xlink:label="xoma_EffectiveDateOfTermLoanExtended_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effective date of term loan extended</label>
    <label xml:lang="en-US" xlink:label="xoma_EffectiveDateOfTermLoanExtended_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Date Of Term Loan Extended</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross cash proceeds received from milestone and licensing payments</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Gross Cash Proceeds Received From Milestone And Licensing Payments</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis spread on variable rate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Basis Spread On Variable Rate1</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest" xlink:type="locator" xlink:label="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest" />
    <label xml:lang="en-US" xlink:label="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Period of monthly payments of principal and interest.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest" xlink:to="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DaysOfPeriodInterest" xlink:type="locator" xlink:label="xoma_DaysOfPeriodInterest" />
    <label xml:lang="en-US" xlink:label="xoma_DaysOfPeriodInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Days of period interest.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DaysOfPeriodInterest" xlink:to="xoma_DaysOfPeriodInterest_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DebtInstrumentMaturityDays" xlink:type="locator" xlink:label="xoma_DebtInstrumentMaturityDays" />
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaturityDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt instrument maturity days.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DebtInstrumentMaturityDays" xlink:to="xoma_DebtInstrumentMaturityDays_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RepaymentOfTermLoan" xlink:type="locator" xlink:label="xoma_RepaymentOfTermLoan" />
    <label xml:lang="en-US" xlink:label="xoma_RepaymentOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Repayment of term loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RepaymentOfTermLoan" xlink:to="xoma_RepaymentOfTermLoan_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable rate basis</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:to="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Description Of Variable Rate Basis</label>
    <label xml:lang="en-US" xlink:label="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period of monthly payments of principal and interest</label>
    <label xml:lang="en-US" xlink:label="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Period Of Monthly Payments Of Principal And Interest</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentMaturityDate" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maturity date</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentMaturityDate" xlink:to="us-gaap_DebtInstrumentMaturityDate_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Maturity Date</label>
    <label xml:lang="en-US" xlink:label="xoma_DaysOfPeriodInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Days of interest, period</label>
    <label xml:lang="en-US" xlink:label="xoma_DaysOfPeriodInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Days Of Period Interest</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaturityDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earliest maturity of loan</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentMaturityDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Maturity Days</label>
    <label xml:lang="en-US" xlink:label="xoma_RepaymentOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Repayment of term loan</label>
    <label xml:lang="en-US" xlink:label="xoma_RepaymentOfTermLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repayment Of Term Loan</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfPrepaymentFee" xlink:type="locator" xlink:label="xoma_PercentageOfPrepaymentFee" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentFee_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of prepayment fee.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfPrepaymentFee" xlink:to="xoma_PercentageOfPrepaymentFee_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan" xlink:type="locator" xlink:label="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of additional interest rate of outstanding loan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan" xlink:to="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of final payment fee of Loan</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Interest Rate Stated Percentage</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentFee_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of prepayment fee</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentFee_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Prepayment Fee</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional interest rate of outstanding payments due</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Additional Interest Rate Of Outstanding Loan</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ExercisablePeriodOfWarrants" xlink:type="locator" xlink:label="xoma_ExercisablePeriodOfWarrants" />
    <label xml:lang="en-US" xlink:label="xoma_ExercisablePeriodOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Represents the exercisable period for warrants beginning on the date of issuance and ending on the earlier to occurrence.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ExercisablePeriodOfWarrants" xlink:to="xoma_ExercisablePeriodOfWarrants_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Aggregate number of shares of common stock called by warrants</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Number Of Securities Called By Warrants Or Rights</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Exercise price of per share</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Exercise Price Of Warrants Or Rights1</label>
    <label xml:lang="en-US" xlink:label="xoma_ExercisablePeriodOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable period of warrants</label>
    <label xml:lang="en-US" xlink:label="xoma_ExercisablePeriodOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Exercisable Period Of Warrants</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" />
    <label xml:lang="en-US" xlink:label="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Fair value of warrant</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure" xlink:to="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrants Not Settleable In Cash Fair Value Disclosure</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredFinanceCostsNet" xlink:type="locator" xlink:label="us-gaap_DeferredFinanceCostsNet" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredFinanceCostsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt issuance costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredFinanceCostsNet" xlink:to="us-gaap_DeferredFinanceCostsNet_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DeferredFinanceCostsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Finance Costs Net</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentCarryingAmount" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentCarryingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Outstanding principal balance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentCarryingAmount" xlink:to="us-gaap_DebtInstrumentCarryingAmount_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentCarryingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Carrying Amount</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_UnamortizedAmountOfDeferredCharges" xlink:type="locator" xlink:label="xoma_UnamortizedAmountOfDeferredCharges" />
    <label xml:lang="en-US" xlink:label="xoma_UnamortizedAmountOfDeferredCharges_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Unamortized amount of deferred charges.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_UnamortizedAmountOfDeferredCharges" xlink:to="xoma_UnamortizedAmountOfDeferredCharges_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_UnamortizedAmountOfDeferredCharges_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unamortized amount of deferred charges</label>
    <label xml:lang="en-US" xlink:label="xoma_UnamortizedAmountOfDeferredCharges_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unamortized Amount Of Deferred Charges</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AmortizationOfDebtDiscountPremium" xlink:type="locator" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium" />
    <label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Non-cash interest expense resulting from amortization of discount and accretion of final payment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfDebtDiscountPremium" xlink:to="us-gaap_AmortizationOfDebtDiscountPremium_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Of Debt Discount Premium</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum" xlink:type="locator" xlink:label="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum" />
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The maximum percentage of aggregate costs of clinical research and development expenses that are funded through a debt instrument under collaborative arrangements and are not incurred by the Company.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum" xlink:to="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:type="locator" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Six-month LIBOR [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:to="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">London Interbank Offered Rate L I B O R [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NovartisNoteAmendmentMember" xlink:type="locator" xlink:label="xoma_NovartisNoteAmendmentMember" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteAmendmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Novartis note amendment.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NovartisNoteAmendmentMember" xlink:to="xoma_NovartisNoteAmendmentMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteAmendmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Secured Note Amendment [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisNoteAmendmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Novartis Note Amendment [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development expenses funded through loan facility, maximum</label>
    <label xml:lang="en-US" xlink:label="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement Research And Development Expense Funded Through Debt Instrument Percentage Maximum</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest rate at period end</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:to="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Interest Rate Effective Percentage</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentDecreaseForgiveness" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentDecreaseForgiveness" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentDecreaseForgiveness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction in outstanding principal amount</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentDecreaseForgiveness" xlink:to="us-gaap_DebtInstrumentDecreaseForgiveness_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentDecreaseForgiveness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Decrease Forgiveness</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_DateOfAgreement" xlink:type="locator" xlink:label="xoma_DateOfAgreement" />
    <label xml:lang="en-US" xlink:label="xoma_DateOfAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The initial date of loan agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DateOfAgreement" xlink:to="xoma_DateOfAgreement_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DebtInstrumentBorrowingCapacity" xlink:type="locator" xlink:label="xoma_DebtInstrumentBorrowingCapacity" />
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The borrowing capacity for a debt instrument under the loan agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DebtInstrumentBorrowingCapacity" xlink:to="xoma_DebtInstrumentBorrowingCapacity_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ServierLoanMember" xlink:type="locator" xlink:label="xoma_ServierLoanMember" />
    <label xml:lang="en-US" xlink:label="xoma_ServierLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Borrowing supported by a written promise to pay an obligation to Servier.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ServierLoanMember" xlink:to="xoma_ServierLoanMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_ServierLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Servier Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_ServierLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Servier Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_DateOfAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Date of agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_DateOfAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Date Of Agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Borrowing capacity under loan agreement</label>
    <label xml:lang="en-US" xlink:label="xoma_DebtInstrumentBorrowingCapacity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Borrowing Capacity</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PaymentOfDebtThroughCashByCollaborator" xlink:type="locator" xlink:label="xoma_PaymentOfDebtThroughCashByCollaborator" />
    <label xml:lang="en-US" xlink:label="xoma_PaymentOfDebtThroughCashByCollaborator_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Payment of debt through cash by collaborator.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PaymentOfDebtThroughCashByCollaborator" xlink:to="xoma_PaymentOfDebtThroughCashByCollaborator_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_PaymentOfDebtThroughCashByCollaborator_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payment of debt through cash by NIBR</label>
    <label xml:lang="en-US" xlink:label="xoma_PaymentOfDebtThroughCashByCollaborator_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payment Of Debt Through Cash By Collaborator</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ForeignCurrencyExchangeRateTranslation1" xlink:type="locator" xlink:label="us-gaap_ForeignCurrencyExchangeRateTranslation1" />
    <label xml:lang="en-US" xlink:label="us-gaap_ForeignCurrencyExchangeRateTranslation1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Euro to US Dollar exchange rates</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ForeignCurrencyExchangeRateTranslation1" xlink:to="us-gaap_ForeignCurrencyExchangeRateTranslation1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ForeignCurrencyExchangeRateTranslation1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Foreign Currency Exchange Rate Translation1</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfPrepaymentChargeOnDebt" xlink:type="locator" xlink:label="xoma_PercentageOfPrepaymentChargeOnDebt" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentChargeOnDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of prepayment charge on debt.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfPrepaymentChargeOnDebt" xlink:to="xoma_PercentageOfPrepaymentChargeOnDebt_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_HerculesTermLoanMember" xlink:type="locator" xlink:label="xoma_HerculesTermLoanMember" />
    <label xml:lang="en-US" xlink:label="xoma_HerculesTermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Borrowing supported by a written promise to pay an obligation to Hercules.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_HerculesTermLoanMember" xlink:to="xoma_HerculesTermLoanMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_HerculesTermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hercules Term Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_HerculesTermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Hercules Term Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentChargeOnDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepayment charge not required to pay</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPrepaymentChargeOnDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Prepayment Charge On Debt</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ClassOfWarrantOrRightExpirationYearAndMonth" xlink:type="locator" xlink:label="xoma_ClassOfWarrantOrRightExpirationYearAndMonth" />
    <label xml:lang="en-US" xlink:label="xoma_ClassOfWarrantOrRightExpirationYearAndMonth_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The month and year (YYYY-MM) in which the warrants or rights expire.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ClassOfWarrantOrRightExpirationYearAndMonth" xlink:to="xoma_ClassOfWarrantOrRightExpirationYearAndMonth_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate number of unregistered shares of common stock called by warrants (in shares)</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise price of warrants (in dollars per share)</label>
    <label xml:lang="en-US" xlink:label="xoma_ClassOfWarrantOrRightExpirationYearAndMonth_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants expiration period</label>
    <label xml:lang="en-US" xlink:label="xoma_ClassOfWarrantOrRightExpirationYearAndMonth_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Expiration Year And Month</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_HerculesLoanMember" xlink:type="locator" xlink:label="xoma_HerculesLoanMember" />
    <label xml:lang="en-US" xlink:label="xoma_HerculesLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Borrowing supported by a written promise to pay an obligation to Hercules.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_HerculesLoanMember" xlink:to="xoma_HerculesLoanMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_HerculesLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hercules Loan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_HerculesLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Hercules Loan [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OtherFinancingsMember" xlink:type="locator" xlink:label="xoma_OtherFinancingsMember" />
    <label xml:lang="en-US" xlink:label="xoma_OtherFinancingsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Other debt obligations not specifically mentioned in the taxonomy.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OtherFinancingsMember" xlink:to="xoma_OtherFinancingsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OtherFinancingsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_OtherFinancingsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Financings [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InterestExpenseAbstract" xlink:type="locator" xlink:label="us-gaap_InterestExpenseAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense and amortization of debt issuance costs [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense [Abstract]</label>
    <label xml:lang="en-US" xlink:label="us-gaap_InterestExpenseDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLossCarryforwardsTable" xlink:type="locator" xlink:label="us-gaap_OperatingLossCarryforwardsTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLossCarryforwardsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Loss Carryforwards [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLossCarryforwardsTable" xlink:to="us-gaap_OperatingLossCarryforwardsTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLossCarryforwardsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxAuthorityNameAxis" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityNameAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority, Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityNameAxis" xlink:to="us-gaap_IncomeTaxAuthorityNameAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority Name [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxAuthorityNameDomain" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityNameDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority, Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityNameDomain" xlink:to="us-gaap_IncomeTaxAuthorityNameDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority Name [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InternalRevenueServiceIRSMember" xlink:type="locator" xlink:label="us-gaap_InternalRevenueServiceIRSMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_InternalRevenueServiceIRSMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InternalRevenueServiceIRSMember" xlink:to="us-gaap_InternalRevenueServiceIRSMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_InternalRevenueServiceIRSMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Internal Revenue Service I R S [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_IncomeTaxAuthorityDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:type="locator" xlink:label="us-gaap_StateAndLocalJurisdictionMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StateAndLocalJurisdictionMember" xlink:to="us-gaap_StateAndLocalJurisdictionMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">State And Local Jurisdiction [Member]</label>
    <loc xlink:href="https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd#stpr_CA" xlink:type="locator" xlink:label="stpr_CA" />
    <label xml:lang="en-US" xlink:label="stpr_CA_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">California [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="stpr_CA" xlink:to="stpr_CA_lbl" />
    <label xml:lang="en-US" xlink:label="stpr_CA_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">CALIFORNIA</label>
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    <label xml:lang="en-US" xlink:label="xoma_NetOperatingLossCarryforwardsExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Operating Loss Carryforwards Expiration Year</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:type="locator" xlink:label="us-gaap_TaxCreditCarryforwardAmount" />
    <label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit carry forward amount</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxCreditCarryforwardAmount" xlink:to="us-gaap_TaxCreditCarryforwardAmount_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Amount</label>
    <label xml:lang="en-US" xlink:label="xoma_TaxCreditCarryforwardExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit carryforward expiration year</label>
    <label xml:lang="en-US" xlink:label="xoma_TaxCreditCarryforwardExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Expiration Year</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage" xlink:type="locator" xlink:label="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating loss carryforwards offset of taxable income percentage.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage" xlink:to="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Loss Carryforwards Offset of Taxable Income Percentage</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards Offset Of Taxable Income Percentage</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions" xlink:type="locator" xlink:label="xoma_UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions" />
    <label xml:lang="en-US" xlink:label="xoma_UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Unrecognized tax benefits increase (decrease) resulting from prior period tax positions.</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" xlink:type="locator" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" />
    <label xml:lang="en-US" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" xlink:to="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefits" />
    <label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning Balance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefits" xlink:to="us-gaap_UnrecognizedTaxBenefits_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" />
    <label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase related to current year tax position</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions</label>
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    <label xml:lang="en-US" xlink:label="xoma_UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits Increases Decreases Resulting From Prior Period Tax Positions</label>
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" />
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:to="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_lbl" />
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    <label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Accrued interest or penalties related to uncertain tax positions</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PlanNameAxis" xlink:type="locator" xlink:label="us-gaap_PlanNameAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PlanNameDomain" xlink:type="locator" xlink:label="us-gaap_PlanNameDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember" xlink:type="locator" xlink:label="xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand fifteen employee stock purchase plan.</label>
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    <label xml:lang="en-US" xlink:label="xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2015 ESPP [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Fifteen Employee Stock Purchase Plan [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandTenLongTermIncentiveAndStockAwardPlanMember" xlink:type="locator" xlink:label="xoma_TwoThousandTenLongTermIncentiveAndStockAwardPlanMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandTenLongTermIncentiveAndStockAwardPlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand ten long term incentive and stock award plan.</label>
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    <label xml:lang="en-US" xlink:label="xoma_TwoThousandTenLongTermIncentiveAndStockAwardPlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Ten Long Term Incentive And Stock Award Plan [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AwardTypeAxis" xlink:type="locator" xlink:label="us-gaap_AwardTypeAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_AwardTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Award Type</label>
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    <label xml:lang="en-US" xlink:label="us-gaap_AwardTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Award Type [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Award</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_IncentiveStockOptionsMember" xlink:type="locator" xlink:label="xoma_IncentiveStockOptionsMember" />
    <label xml:lang="en-US" xlink:label="xoma_IncentiveStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Incentive stock options.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IncentiveStockOptionsMember" xlink:to="xoma_IncentiveStockOptionsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_IncentiveStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Incentive Stock Options [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_IncentiveStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Incentive Stock Options [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OptionsAndStockAppreciationRightsMember" xlink:type="locator" xlink:label="xoma_OptionsAndStockAppreciationRightsMember" />
    <label xml:lang="en-US" xlink:label="xoma_OptionsAndStockAppreciationRightsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Options and stock appreciation rights.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OptionsAndStockAppreciationRightsMember" xlink:to="xoma_OptionsAndStockAppreciationRightsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OptionsAndStockAppreciationRightsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options and Stock Appreciation Rights [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_OptionsAndStockAppreciationRightsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Options And Stock Appreciation Rights [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OtherTypesOfStockAwardsMember" xlink:type="locator" xlink:label="xoma_OtherTypesOfStockAwardsMember" />
    <label xml:lang="en-US" xlink:label="xoma_OtherTypesOfStockAwardsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Other types of stock awards.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OtherTypesOfStockAwardsMember" xlink:to="xoma_OtherTypesOfStockAwardsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OtherTypesOfStockAwardsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Types of Stock Awards [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_OtherTypesOfStockAwardsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Types Of Stock Awards [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LongTermIncentivePlanMember" xlink:type="locator" xlink:label="xoma_LongTermIncentivePlanMember" />
    <label xml:lang="en-US" xlink:label="xoma_LongTermIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The equity-based compensation arrangement plan approved in July of 2010 by the Company&apos;s stockholders that grants stock options and other stock-based awards to employees, consultants, and directors. The Long Term Incentive Plan is intended to consolidate the Company&apos;s long-term incentive compensation under a single plan, by replacing the Option Plan, the Restricted Plan and the 1992 Directors Share Option Plan (the "Directors Plan") going forward, and to provide a more current set of terms pursuant to which to provide this type of compensation.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LongTermIncentivePlanMember" xlink:to="xoma_LongTermIncentivePlanMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LongTermIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long Term Incentive Plan [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LongTermIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Incentive Plan [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:type="locator" xlink:label="us-gaap_TitleOfIndividualAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_TitleOfIndividualAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of Individual</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TitleOfIndividualAxis" xlink:to="us-gaap_TitleOfIndividualAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_TitleOfIndividualAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Title Of Individual [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:type="locator" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Relationship to Entity</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Title Of Individual With Relationship To Entity [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NonExecutiveEmployeeMember" xlink:type="locator" xlink:label="xoma_NonExecutiveEmployeeMember" />
    <label xml:lang="en-US" xlink:label="xoma_NonExecutiveEmployeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Person employed by the Company with no responsibility for governing the entity.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NonExecutiveEmployeeMember" xlink:to="xoma_NonExecutiveEmployeeMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NonExecutiveEmployeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non Executive Employee [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_NonExecutiveEmployeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Non Executive Employee [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DirectorMember" xlink:type="locator" xlink:label="us-gaap_DirectorMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_DirectorMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Directors [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DirectorMember" xlink:to="us-gaap_DirectorMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DirectorMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Director [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:type="locator" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_EmployeeStockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock Options [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeStockOptionMember" xlink:to="us-gaap_EmployeeStockOptionMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_EmployeeStockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Stock Option [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PerformanceSharesMember" xlink:type="locator" xlink:label="us-gaap_PerformanceSharesMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_PerformanceSharesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Performance Shares [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PerformanceSharesMember" xlink:to="us-gaap_PerformanceSharesMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PerformanceSharesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Performance Shares [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ExecutiveOfficerMember" xlink:type="locator" xlink:label="us-gaap_ExecutiveOfficerMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_ExecutiveOfficerMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Executives [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ExecutiveOfficerMember" xlink:to="us-gaap_ExecutiveOfficerMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ExecutiveOfficerMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Executive Officer [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ServiceBasedStockOptionsMember" xlink:type="locator" xlink:label="xoma_ServiceBasedStockOptionsMember" />
    <label xml:lang="en-US" xlink:label="xoma_ServiceBasedStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Service-based stock options.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ServiceBasedStockOptionsMember" xlink:to="xoma_ServiceBasedStockOptionsMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_ServiceBasedStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Service-Based Stock Options [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_ServiceBasedStockOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Service Based Stock Options [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Stock Units (RSUs) [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestrictedStockUnitsRSUMember" xlink:to="us-gaap_RestrictedStockUnitsRSUMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock Units R S U [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage related to employees to purchase shares at the lower fair market value at offering period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Purchase Price Of Common Stock Percent</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions" xlink:type="locator" xlink:label="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers the percentage of compensation deduction in eligible employees salary to purchase entity common stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions" xlink:to="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock reserved for future issuance (in shares)</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of compensation of eligible employees to purchase shares of entity common stock at discount through payroll deductions</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Compensation Of Eligible Employees To Purchase Shares Of Entity Common Stock At Discount Through Payroll Deductions</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase in aggregate number of shares authorized for issuance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares authorized for issuance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase in shares per person award limits</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Maximum Number Of Shares Per Employee</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares purchased (in shares)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Shares Purchased For Award</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount" xlink:type="locator" xlink:label="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount" />
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum amount per employee over 50 years old, by the terms of the plan, that the employer may contribute to a defined contribution plan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount" xlink:to="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum" xlink:type="locator" xlink:label="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum" />
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The age requirement for participants to be eligible for a catch-up contribution amount to a defined contribution plan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum" xlink:to="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum" xlink:type="locator" xlink:label="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum" />
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum percentage of employees&apos; salary deferred for which the employer contributes a matching contribution to a defined contribution plan.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum" xlink:to="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage" xlink:type="locator" xlink:label="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage" />
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The percentage of defined contribution plan expense paid through the issuance of common shares.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage" xlink:to="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent" xlink:type="locator" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum annual contribution per employee (in hundredths)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent" xlink:to="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Maximum Annual Contributions Per Employee Percent</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount" xlink:type="locator" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum annual contribution per employee</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount" xlink:to="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Maximum Annual Contributions Per Employee Amount</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum annual contribution per employee over 50 years old</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Maximum Annual Contribution Per Employee Over50 Years Old Amount</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Age requirement for participant to be eligible for a catch-up contribution, minimum</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Age Required For Catch Up Contribution Minimum</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employer matching contribution percentage, maximum (in hundredths)</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Employer Matching Contribution Percent Of Employer Salary Deferred Maximum</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized" xlink:type="locator" xlink:label="us-gaap_DefinedContributionPlanCostRecognized" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanCostRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Deferred savings plan expense</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DefinedContributionPlanCostRecognized" xlink:to="us-gaap_DefinedContributionPlanCostRecognized_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanCostRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Cost Recognized</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred savings plan expense paid in common shares (in hundredths)</label>
    <label xml:lang="en-US" xlink:label="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Cost Recognized And Paid Through Issuance Of Common Shares Percentage</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription" xlink:type="locator" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Description of the period in which the equity-based award expires.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription" xlink:to="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expiration period</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Expiration Period Description</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding" xlink:type="locator" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award number of shares to be issued upon exercise of options and RSUs outstanding.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding" xlink:to="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares available for grant</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares of common stock to be issued upon exercise of options and RSUs outstanding (in shares)</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares To Be Issued Upon Exercise Of Options And R S Us Outstanding</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus" xlink:type="locator" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Minimum age required for employees to qualify for immediate vesting of RSUs.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus" xlink:to="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge" xlink:type="locator" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Threshold years required for retirement age (defined as employees that are a minimum of 55 years of age and the sum of their age plus years of full-time employment with the Company).</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge" xlink:to="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum age required for employees to qualify for immediate vesting of RSUs</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Minimum Age Required For Immediate Vesting Of Rsus</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Threshold years required for retirement age</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Threshold Period For Retirement Age</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of stock options granted to members of board of directors, executives, and non-executive employees</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue" xlink:type="locator" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue" />
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award options grant date fair value.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue" xlink:to="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of options outstanding, non-vested options</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of options vested</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested Number Of Shares</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant date fair value</label>
    <label xml:lang="en-US" xlink:label="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Grant Date Fair Value</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock options cancelled</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Number of shares, Outstanding at beginning of year</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of shares, Granted</label>
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Number of shares, Exercised</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Number of shares, Forfeited, expired or cancelled</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Number of shares, Outstanding at end of year</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Number of shares, Exercisable at end of period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Weighted Average Exercise Price Per Share, Outstanding at January 1, 2018</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
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    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Denominator</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number Of Shares Outstanding [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of dilutive stock options</label>
    <label xml:lang="en-US" xlink:label="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable To Dilutive Effect Of Stock Options</label>
    <label xml:lang="en-US" xlink:label="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of dilutive warrants</label>
    <label xml:lang="en-US" xlink:label="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable To Dilutive Effect Of Warrants</label>
    <label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Weighted average shares used in computing diluted net (loss) income per share available to common stockholders</label>
    <label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Basic net (loss) income per share of common stock</label>
    <label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Diluted net (loss) income per share of common stock</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_WriteOffOfCapitalizedOfferingCost" xlink:type="locator" xlink:label="xoma_WriteOffOfCapitalizedOfferingCost" />
    <label xml:lang="en-US" xlink:label="xoma_WriteOffOfCapitalizedOfferingCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Write-off of capitalized offering cost.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_WriteOffOfCapitalizedOfferingCost" xlink:to="xoma_WriteOffOfCapitalizedOfferingCost_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock" xlink:type="locator" xlink:label="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock" />
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Gross proceeds from issuance of ccommon stock and preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock" xlink:to="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_RightsOfferingAmount" xlink:type="locator" xlink:label="xoma_RightsOfferingAmount" />
    <label xml:lang="en-US" xlink:label="xoma_RightsOfferingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Rights offering amount.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RightsOfferingAmount" xlink:to="xoma_RightsOfferingAmount_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class Of Warrant Or Right [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_ClassOfWarrantOrRightTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Table]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SeriesXPreferredStockMember" xlink:type="locator" xlink:label="xoma_SeriesXPreferredStockMember" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series X preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SeriesXPreferredStockMember" xlink:to="xoma_SeriesXPreferredStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series X Preferred Stock [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SeriesXPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series X Preferred Stock [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SeriesYPreferredStockMember" xlink:type="locator" xlink:label="xoma_SeriesYPreferredStockMember" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesYPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series Y preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SeriesYPreferredStockMember" xlink:to="xoma_SeriesYPreferredStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesYPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series Y Preferred Stock [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SeriesYPreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series Y Preferred Stock [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SeriesYConvertiblePreferredStockMember" xlink:type="locator" xlink:label="xoma_SeriesYConvertiblePreferredStockMember" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series Y convertible preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SeriesYConvertiblePreferredStockMember" xlink:to="xoma_SeriesYConvertiblePreferredStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series Y Convertible Preferred Stock [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series Y Convertible Preferred Stock [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SeriesXAndSeriesYConvertiblePreferredStockMember" xlink:type="locator" xlink:label="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series X and series Y convertible preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember" xlink:to="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series X and Series Y Convertible Preferred Stock [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series X And Series Y Convertible Preferred Stock [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_OwnershipAxis" xlink:type="locator" xlink:label="srt_OwnershipAxis" />
    <label xml:lang="en-US" xlink:label="srt_OwnershipAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Ownership</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_OwnershipAxis" xlink:to="srt_OwnershipAxis_lbl" />
    <label xml:lang="en-US" xlink:label="srt_OwnershipAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Ownership [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_OwnershipDomain" xlink:type="locator" xlink:label="srt_OwnershipDomain" />
    <label xml:lang="en-US" xlink:label="srt_OwnershipDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Ownership</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_OwnershipDomain" xlink:to="srt_OwnershipDomain_lbl" />
    <label xml:lang="en-US" xlink:label="srt_OwnershipDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Ownership [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_BiotechnologyValueFundLPMember" xlink:type="locator" xlink:label="xoma_BiotechnologyValueFundLPMember" />
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Biotechnology Value Fund, L.P.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_BiotechnologyValueFundLPMember" xlink:to="xoma_BiotechnologyValueFundLPMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">BVF [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Biotechnology Value Fund L P [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class Of Warrant Or Right [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_RightsOfferingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rights offering amount</label>
    <label xml:lang="en-US" xlink:label="xoma_RightsOfferingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Rights Offering Amount</label>
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Total number of shares issued</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate gross proceeds from issuance of common stock and preferred stock</label>
    <label xml:lang="en-US" xlink:label="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Gross Proceeds From Issuance Of Ccommon Stock And Preferred Stock</label>
    <label xml:lang="en-US" xlink:label="xoma_WriteOffOfCapitalizedOfferingCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Offering costs offset against proceeds sale of common stock and preferred stock</label>
    <label xml:lang="en-US" xlink:label="xoma_WriteOffOfCapitalizedOfferingCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Write Off Of Capitalized Offering Cost</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net proceeds from issuance of common stock and preferred stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Or Sale Of Equity</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PreferredStockConversionPricePerShare" xlink:type="locator" xlink:label="xoma_PreferredStockConversionPricePerShare" />
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockConversionPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Preferred stock conversion price per share.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PreferredStockConversionPricePerShare" xlink:to="xoma_PreferredStockConversionPricePerShare_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_ConvertibleCommonStockSharesIssuedUponConversion" xlink:type="locator" xlink:label="xoma_ConvertibleCommonStockSharesIssuedUponConversion" />
    <label xml:lang="en-US" xlink:label="xoma_ConvertibleCommonStockSharesIssuedUponConversion_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Convertible common stock shares issued upon conversion.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ConvertibleCommonStockSharesIssuedUponConversion" xlink:to="xoma_ConvertibleCommonStockSharesIssuedUponConversion_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfPreferredStockConversionBlockerProvision" xlink:type="locator" xlink:label="xoma_PercentageOfPreferredStockConversionBlockerProvision" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPreferredStockConversionBlockerProvision_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of preferred stock conversion blocker provision.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfPreferredStockConversionBlockerProvision" xlink:to="xoma_PercentageOfPreferredStockConversionBlockerProvision_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock" xlink:type="locator" xlink:label="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock" />
    <label xml:lang="en-US" xlink:label="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Minority interest ownership percentage after conversion of convertible preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock" xlink:to="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Preferred stock, stated value</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:type="locator" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Conversion of preferred stock into registered common stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:to="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Preferred Stock Shares Issued Upon Conversion</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockConversionPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock conversion price per share</label>
    <label xml:lang="en-US" xlink:label="xoma_PreferredStockConversionPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Conversion Price Per Share</label>
    <label xml:lang="en-US" xlink:label="xoma_ConvertibleCommonStockSharesIssuedUponConversion_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total number of shares of common stock issued upon conversion</label>
    <label xml:lang="en-US" xlink:label="xoma_ConvertibleCommonStockSharesIssuedUponConversion_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Common Stock Shares Issued Upon Conversion</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPreferredStockConversionBlockerProvision_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of convertible preferred stock conversion blocker provision</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfPreferredStockConversionBlockerProvision_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Preferred Stock Conversion Blocker Provision</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" xlink:type="locator" xlink:label="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" />
    <label xml:lang="en-US" xlink:label="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Ownership percentage on outstanding shares</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" xlink:to="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minority Interest Ownership Percentage By Noncontrolling Owners</label>
    <label xml:lang="en-US" xlink:label="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Ownership percentage on outstanding shares</label>
    <label xml:lang="en-US" xlink:label="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minority Interest Ownership Percentage After Conversion Of Convertible Preferred Stock</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:type="locator" xlink:label="us-gaap_ConversionOfStockSharesConverted1" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConversionOfStockSharesConverted1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Preferred shares converted</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConversionOfStockSharesConverted1" xlink:to="us-gaap_ConversionOfStockSharesConverted1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConversionOfStockSharesConverted1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Conversion Of Stock Shares Converted1</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SeriesXConvertiblePreferredStockMember" xlink:type="locator" xlink:label="xoma_SeriesXConvertiblePreferredStockMember" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series X convertible preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SeriesXConvertiblePreferredStockMember" xlink:to="xoma_SeriesXConvertiblePreferredStockMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SeriesXConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series X Convertible Preferred Stock [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SeriesXConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series X Convertible Preferred Stock [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember" xlink:type="locator" xlink:label="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember" />
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Biotechnology Value Fund LP and certain of its Affiliates.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember" xlink:to="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">BVF [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Biotechnology Value Fund L P And Certain Of Its Affiliates [Member]</label>
    <label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Sale of shares</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Cash proceeds from issuance of common stock and convertible preferred stock</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SharePrice" xlink:type="locator" xlink:label="us-gaap_SharePrice" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock share price</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Price</label>
    <label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Preferred stock, stated value</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock" xlink:type="locator" xlink:label="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock" />
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value of common stock amount exceeded allocated purchase price of convertible preferred stock.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock" xlink:to="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair value of common stock amount exceeded purchase price of convertible preferred stock</label>
    <label xml:lang="en-US" xlink:label="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Of Common Stock Amount Exceeded Allocated Purchase Price Of Convertible Preferred Stock</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued" xlink:type="locator" xlink:label="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued" />
    <label xml:lang="en-US" xlink:label="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">At market issuance sales agreement maximum value of common stock to be issued.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued" xlink:to="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares" xlink:type="locator" xlink:label="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The percentage of sales commission to gross proceeds paid to sales agents for the sale of the Company&apos;s common shares.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares" xlink:to="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_TwoThousandEighteenAtMarketAgreementMember" xlink:type="locator" xlink:label="xoma_TwoThousandEighteenAtMarketAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandEighteenAtMarketAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand eighteen at the market agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TwoThousandEighteenAtMarketAgreementMember" xlink:to="xoma_TwoThousandEighteenAtMarketAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandEighteenAtMarketAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2018 ATM Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TwoThousandEighteenAtMarketAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Eighteen At Market Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AtmAgreement4Member" xlink:type="locator" xlink:label="xoma_AtmAgreement4Member" />
    <label xml:lang="en-US" xlink:label="xoma_AtmAgreement4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">ATM agreement 4.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AtmAgreement4Member" xlink:to="xoma_AtmAgreement4Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_AtmAgreement4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2015 ATM Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_AtmAgreement4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Atm Agreement4 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sales commission paid per transaction (in hundredths)</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Gross Proceeds Paid To Agent For Sale Of Common Shares</label>
    <label xml:lang="en-US" xlink:label="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum amount of shares can be issued</label>
    <label xml:lang="en-US" xlink:label="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">At Market Issuance Sales Agreement Maximum Value Of Common Stock To Be Issued</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_AgreementExpirationDate" xlink:type="locator" xlink:label="xoma_AgreementExpirationDate" />
    <label xml:lang="en-US" xlink:label="xoma_AgreementExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Agreement expiration date.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AgreementExpirationDate" xlink:to="xoma_AgreementExpirationDate_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Proceeds from issuance of common stock</label>
    <label xml:lang="en-US" xlink:label="xoma_WriteOffOfCapitalizedOfferingCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Offering costs offset against proceeds upon sale of common stock</label>
    <label xml:lang="en-US" xlink:label="xoma_AgreementExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Agreement expired date</label>
    <label xml:lang="en-US" xlink:label="xoma_AgreementExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Agreement Expiration Date</label>
    <label xml:lang="en-US" xlink:label="xoma_NovartisInternationalPharmaceuticalLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Novartis [Member]</label>
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of common stock agreed to issue and sell</label>
    <label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock sale price</label>
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate purchase price of common stock agreed to issue and sell</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SaleOfStockTransactionDate" xlink:type="locator" xlink:label="us-gaap_SaleOfStockTransactionDate" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockTransactionDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock purchase agreement date</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockTransactionDate" xlink:to="us-gaap_SaleOfStockTransactionDate_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockTransactionDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Transaction Date</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_IssuanceDateOfCommonStockWarrants" xlink:type="locator" xlink:label="xoma_IssuanceDateOfCommonStockWarrants" />
    <label xml:lang="en-US" xlink:label="xoma_IssuanceDateOfCommonStockWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Issuance date of common stock warrants.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_IssuanceDateOfCommonStockWarrants" xlink:to="xoma_IssuanceDateOfCommonStockWarrants_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommonStockWarrantsExpirationDate" xlink:type="locator" xlink:label="xoma_CommonStockWarrantsExpirationDate" />
    <label xml:lang="en-US" xlink:label="xoma_CommonStockWarrantsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock warrants expiration date.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommonStockWarrantsExpirationDate" xlink:to="xoma_CommonStockWarrantsExpirationDate_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FiveYearWarrantsIssuedFirstRangeMember" xlink:type="locator" xlink:label="xoma_FiveYearWarrantsIssuedFirstRangeMember" />
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedFirstRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The first range of security that gives the holder the right to purchase shares of stock in accordance with the terms of the instrument, usually upon payment of a specified amount.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FiveYearWarrantsIssuedFirstRangeMember" xlink:to="xoma_FiveYearWarrantsIssuedFirstRangeMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedFirstRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Five Year Warrants Issued in February 2015 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedFirstRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Five Year Warrants Issued First Range [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_FiveYearWarrantsIssuedSecondRangeMember" xlink:type="locator" xlink:label="xoma_FiveYearWarrantsIssuedSecondRangeMember" />
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedSecondRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The second range of security that gives the holder the right to purchase shares of stock in accordance with the terms of the instrument, usually upon payment of a specified amount.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FiveYearWarrantsIssuedSecondRangeMember" xlink:to="xoma_FiveYearWarrantsIssuedSecondRangeMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedSecondRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Five Year Warrants Issued in February 2016 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_FiveYearWarrantsIssuedSecondRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Five Year Warrants Issued Second Range [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_TenYearWarrantsIssuedThirdRangeMember" xlink:type="locator" xlink:label="xoma_TenYearWarrantsIssuedThirdRangeMember" />
    <label xml:lang="en-US" xlink:label="xoma_TenYearWarrantsIssuedThirdRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The third range of security that gives the holder the right to purchase shares of stock in accordance with the terms of the instrument, usually upon payment of a specified amount.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_TenYearWarrantsIssuedThirdRangeMember" xlink:to="xoma_TenYearWarrantsIssuedThirdRangeMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_TenYearWarrantsIssuedThirdRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Ten Year Warrants Issued in May 2018 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_TenYearWarrantsIssuedThirdRangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Ten Year Warrants Issued Third Range [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByLiabilityClassAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability Class</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByLiabilityClassAxis" xlink:to="us-gaap_FairValueByLiabilityClassAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Liability Class [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value by Liability Class</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Liability Class [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_StockholdersEquityMember" xlink:type="locator" xlink:label="xoma_StockholdersEquityMember" />
    <label xml:lang="en-US" xlink:label="xoma_StockholdersEquityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stockholders equity.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_StockholdersEquityMember" xlink:to="xoma_StockholdersEquityMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_StockholdersEquityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Stockholders&apos; Equity [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_StockholdersEquityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_IssuanceDateOfCommonStockWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance Date</label>
    <label xml:lang="en-US" xlink:label="xoma_IssuanceDateOfCommonStockWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Date Of Common Stock Warrants</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockWarrantsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expiration Date</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockWarrantsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Warrants Expiration Date</label>
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Exercise price of warrants (in dollars per share)</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Warrant outstanding (in shares)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightOutstanding" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Outstanding</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ThirdPartyConsultantMember" xlink:type="locator" xlink:label="xoma_ThirdPartyConsultantMember" />
    <label xml:lang="en-US" xlink:label="xoma_ThirdPartyConsultantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Third-party consultant.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ThirdPartyConsultantMember" xlink:to="xoma_ThirdPartyConsultantMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_ThirdPartyConsultantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Third-Party Consultant [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_ThirdPartyConsultantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Third Party Consultant [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CommonStockWarrantsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Warrants expiration period</label>
    <label xml:lang="en-US" xlink:label="us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated fair value of warrants</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_ContractualObligationEstimatedMilestonePayments" xlink:type="locator" xlink:label="xoma_ContractualObligationEstimatedMilestonePayments" />
    <label xml:lang="en-US" xlink:label="xoma_ContractualObligationEstimatedMilestonePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Reflects estimated obligations that are due and payable upon achievement of certain criteria categorized as developmental, regulatory, or commercial milestones.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_ContractualObligationEstimatedMilestonePayments" xlink:to="xoma_ContractualObligationEstimatedMilestonePayments_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommitmentsAndContingenciesLineItems" xlink:type="locator" xlink:label="xoma_CommitmentsAndContingenciesLineItems" />
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommitmentsAndContingenciesLineItems" xlink:to="xoma_CommitmentsAndContingenciesLineItems_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_CommitmentsAndContingenciesTable" xlink:type="locator" xlink:label="xoma_CommitmentsAndContingenciesTable" />
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CommitmentsAndContingenciesTable" xlink:to="xoma_CommitmentsAndContingenciesTable_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Table]</label>
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_StatementGeographicalAxis" xlink:type="locator" xlink:label="srt_StatementGeographicalAxis" />
    <label xml:lang="en-US" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_StatementGeographicalAxis_lbl" />
    <label xml:lang="en-US" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Geographical [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_SegmentGeographicalDomain" xlink:type="locator" xlink:label="srt_SegmentGeographicalDomain" />
    <label xml:lang="en-US" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_SegmentGeographicalDomain_lbl" />
    <label xml:lang="en-US" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Segment Geographical [Domain]</label>
    <label xml:lang="en-US" xlink:label="stpr_CA_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Berkeley, California [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LeaseArrangementTypeAxis" xlink:type="locator" xlink:label="us-gaap_LeaseArrangementTypeAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease Arrangement, Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseArrangementTypeAxis" xlink:to="us-gaap_LeaseArrangementTypeAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Arrangement Type [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:type="locator" xlink:label="us-gaap_LeaseArrangementTypeDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease Arrangement, Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseArrangementTypeDomain" xlink:to="us-gaap_LeaseArrangementTypeDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Arrangement Type [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember" xlink:type="locator" xlink:label="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember" />
    <label xml:lang="en-US" xlink:label="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lease agreement commenced in Septembr two thousand and seventeen.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember" xlink:to="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Llease Agreement Commenced in Septembr 2017 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Agreement Commenced In Septembr Two Thousand And Seventeen [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember" xlink:type="locator" xlink:label="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublease agreement commenced on december twenty six two thousand and seventeen.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember" xlink:to="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease Agreement Commenced on December 26, 2017 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Agreement Commenced On December Twenty Six Two Thousand And Seventeen [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:type="locator" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loss Contingency Nature</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:to="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Loss Contingencies By Nature Of Contingency [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:type="locator" xlink:label="us-gaap_LossContingencyNatureDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_LossContingencyNatureDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loss Contingency, Nature</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingencyNatureDomain" xlink:to="us-gaap_LossContingencyNatureDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LossContingencyNatureDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Loss Contingency Nature [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StandbyLettersOfCreditMember" xlink:type="locator" xlink:label="us-gaap_StandbyLettersOfCreditMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Standby Letter of Credit [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StandbyLettersOfCreditMember" xlink:to="us-gaap_StandbyLettersOfCreditMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Standby Letters Of Credit [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember" xlink:type="locator" xlink:label="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublease agreement commenced on may one two thousand and eighteen.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember" xlink:to="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease Agreement Commenced on May 1,2018 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Agreement Commenced On May One Two Thousand And Eighteen [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RestructuringChargesMember" xlink:type="locator" xlink:label="us-gaap_RestructuringChargesMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringChargesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring Charges [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestructuringChargesMember" xlink:to="us-gaap_RestructuringChargesMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RestructuringChargesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Charges [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember" xlink:type="locator" xlink:label="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublease agreement commenced on october twenty four two thousand and eighteen.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember" xlink:to="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease Agreement Commenced on October 24,2018 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Agreement Commenced On October Twenty Four Two Thousand And Eighteen [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_CommitmentsAndContingenciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractualObligationEstimatedMilestonePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimate of milestone payments</label>
    <label xml:lang="en-US" xlink:label="xoma_ContractualObligationEstimatedMilestonePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contractual Obligation Estimated Milestone Payments</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear" xlink:type="locator" xlink:label="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear" />
    <label xml:lang="en-US" xlink:label="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lessee leasing arrangements operating leases expiry month and year.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear" xlink:to="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesNumberOfLeasedFacilities" xlink:type="locator" xlink:label="xoma_OperatingLeasesNumberOfLeasedFacilities" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfLeasedFacilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases, number of leased facilities.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesNumberOfLeasedFacilities" xlink:to="xoma_OperatingLeasesNumberOfLeasedFacilities_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, expiry date</label>
    <label xml:lang="en-US" xlink:label="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Leasing Arrangements Operating Leases Expiry Month And Year</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfLeasedFacilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, number of leased facilities</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesNumberOfLeasedFacilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Number Of Leased Facilities</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeaseCommencementDate" xlink:type="locator" xlink:label="xoma_OperatingLeaseCommencementDate" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease commencement date.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeaseCommencementDate" xlink:to="xoma_OperatingLeaseCommencementDate_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_LeasePaymentsTerm" xlink:type="locator" xlink:label="xoma_LeasePaymentsTerm" />
    <label xml:lang="en-US" xlink:label="xoma_LeasePaymentsTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lease payments term.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_LeasePaymentsTerm" xlink:to="xoma_LeasePaymentsTerm_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract" />
    <label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease agreement term</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseTermOfContract" xlink:to="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Term Of Contract</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease commencement date</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Commencement Date</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total lease payments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due</label>
    <label xml:lang="en-US" xlink:label="xoma_LeasePaymentsTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease payments term</label>
    <label xml:lang="en-US" xlink:label="xoma_LeasePaymentsTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Payments Term</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LeaseAndRentalExpense" xlink:type="locator" xlink:label="us-gaap_LeaseAndRentalExpense" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseAndRentalExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, total rental expense</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseAndRentalExpense" xlink:to="us-gaap_LeaseAndRentalExpense_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LeaseAndRentalExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease And Rental Expense</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SubleasedFacilityNumberOfPortions" xlink:type="locator" xlink:label="xoma_SubleasedFacilityNumberOfPortions" />
    <label xml:lang="en-US" xlink:label="xoma_SubleasedFacilityNumberOfPortions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Subleased facility number of portions.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SubleasedFacilityNumberOfPortions" xlink:to="xoma_SubleasedFacilityNumberOfPortions_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesSubleaseCommencementDate" xlink:type="locator" xlink:label="xoma_OperatingLeasesSubleaseCommencementDate" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases, sublease commencement date.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesSubleaseCommencementDate" xlink:to="xoma_OperatingLeasesSubleaseCommencementDate_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable" xlink:type="locator" xlink:label="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases sublease revenue plus reimbursement of operating expenses receivable.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable" xlink:to="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesSubleaseExpiryDate" xlink:type="locator" xlink:label="xoma_OperatingLeasesSubleaseExpiryDate" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseExpiryDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases sublease expiration date.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesSubleaseExpiryDate" xlink:to="xoma_OperatingLeasesSubleaseExpiryDate_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesLossOnSublease" xlink:type="locator" xlink:label="xoma_OperatingLeasesLossOnSublease" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases loss on sublease.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesLossOnSublease" xlink:to="xoma_OperatingLeasesLossOnSublease_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SubleasedFacilityNumberOfPortions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, number of portions of leased facilities</label>
    <label xml:lang="en-US" xlink:label="xoma_SubleasedFacilityNumberOfPortions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subleased Facility Number Of Portions</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, sublease commencement date</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Sublease Commencement Date</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases sublease income plus reimbursement of operating expenses receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Sublease Revenue Plus Reimbursement Of Operating Expenses Receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseExpiryDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases sublease expiry date</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseExpiryDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Sublease Expiry Date</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsForTenantImprovements" xlink:type="locator" xlink:label="us-gaap_PaymentsForTenantImprovements" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsForTenantImprovements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease tenant improvement allowance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForTenantImprovements" xlink:to="us-gaap_PaymentsForTenantImprovements_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PaymentsForTenantImprovements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments For Tenant Improvements</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Sublease loss</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesLossOnSublease_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Loss On Sublease</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:type="locator" xlink:label="us-gaap_LettersOfCreditOutstandingAmount" />
    <label xml:lang="en-US" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Letter of credit amount</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LettersOfCreditOutstandingAmount" xlink:to="us-gaap_LettersOfCreditOutstandingAmount_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Letters Of Credit Outstanding Amount</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProceedsFromLinesOfCredit" xlink:type="locator" xlink:label="us-gaap_ProceedsFromLinesOfCredit" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromLinesOfCredit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Funds drawn from letter of credit</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromLinesOfCredit" xlink:to="us-gaap_ProceedsFromLinesOfCredit_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromLinesOfCredit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Lines Of Credit</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue" xlink:to="us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Income Statement Sublease Revenue</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PayablesToBrokerDealersAndClearingOrganizations" xlink:type="locator" xlink:label="us-gaap_PayablesToBrokerDealersAndClearingOrganizations" />
    <label xml:lang="en-US" xlink:label="us-gaap_PayablesToBrokerDealersAndClearingOrganizations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease broker commissions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PayablesToBrokerDealersAndClearingOrganizations" xlink:to="us-gaap_PayablesToBrokerDealersAndClearingOrganizations_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_PayablesToBrokerDealersAndClearingOrganizations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payables To Broker Dealers And Clearing Organizations</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesSubleaseRevenueReceivable" xlink:type="locator" xlink:label="xoma_OperatingLeasesSubleaseRevenueReceivable" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases sublease revenue receivable.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesSubleaseRevenueReceivable" xlink:to="xoma_OperatingLeasesSubleaseRevenueReceivable_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases sublease income receivable</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesSubleaseRevenueReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Sublease Revenue Receivable</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractually required future rental payments receivable on non-cancelable subleasing arrangements current.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractually required future rental payments receivable on non-cancelable subleasing arrangements year two.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractually required future rental payments receivable on non-cancelable subleasing arrangements year three.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractually required future rental payments receivable on non-cancelable subleasing arrangements year four.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractually required future rental payments receivable on non-cancelable subleasing arrangements year five.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases future minimum payments due sublease rentals thereafter.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated future minimum rent payments [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due [Abstract]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2019</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Current</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due In Two Years</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2021</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due In Three Years</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2022</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due In Four Years</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2023</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due In Five Years</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Thereafter</label>
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total minimum lease payments</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract" xlink:type="locator" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases future minimum payments due sublease income.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract" xlink:to="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated future minimum sublease income [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Income [Abstract]</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2019</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Current</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Year Two</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2021</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Year Three</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2022</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Year Four</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2023</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Year Five</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</label>
    <label xml:lang="en-US" xlink:label="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Sublease Rentals Thereafter</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals" xlink:type="locator" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total minimum lease payments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Future Minimum Payments Due Future Minimum Sublease Rentals</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskTable" xlink:to="us-gaap_ConcentrationRiskTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskByTypeAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskByTypeAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk By Type [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskTypeDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskTypeDomain" xlink:to="us-gaap_ConcentrationRiskTypeDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk Type [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:type="locator" xlink:label="us-gaap_CustomerConcentrationRiskMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_CustomerConcentrationRiskMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer Concentration Risk [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CustomerConcentrationRiskMember" xlink:to="us-gaap_CustomerConcentrationRiskMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_CustomerConcentrationRiskMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Customer Concentration Risk [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk Benchmark</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk By Benchmark [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk Benchmark</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk Benchmark [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SalesRevenueGoodsNetMember" xlink:type="locator" xlink:label="us-gaap_SalesRevenueGoodsNetMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_SalesRevenueGoodsNetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenues [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SalesRevenueGoodsNetMember" xlink:to="us-gaap_SalesRevenueGoodsNetMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SalesRevenueGoodsNetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sales Revenue Goods Net [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsReceivableMember" xlink:type="locator" xlink:label="us-gaap_AccountsReceivableMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts Receivable [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsReceivableMember" xlink:to="us-gaap_AccountsReceivableMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MajorCustomersAxis" xlink:type="locator" xlink:label="srt_MajorCustomersAxis" />
    <label xml:lang="en-US" xlink:label="srt_MajorCustomersAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_MajorCustomersAxis_lbl" />
    <label xml:lang="en-US" xlink:label="srt_MajorCustomersAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Major Customers [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_NameOfMajorCustomerDomain" xlink:type="locator" xlink:label="srt_NameOfMajorCustomerDomain" />
    <label xml:lang="en-US" xlink:label="srt_NameOfMajorCustomerDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_NameOfMajorCustomerDomain" xlink:to="srt_NameOfMajorCustomerDomain_lbl" />
    <label xml:lang="en-US" xlink:label="srt_NameOfMajorCustomerDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Name Of Major Customer [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_Partner1Member" xlink:type="locator" xlink:label="xoma_Partner1Member" />
    <label xml:lang="en-US" xlink:label="xoma_Partner1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Name or description of a single external partner 1 that accounts for 10 percent or more of the entity&apos;s revenues.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_Partner1Member" xlink:to="xoma_Partner1Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_Partner1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Partner 1 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_Partner1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Partner1 [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_Partner2Member" xlink:type="locator" xlink:label="xoma_Partner2Member" />
    <label xml:lang="en-US" xlink:label="xoma_Partner2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Name or description of a single external partner 2 that accounts for 10 percent or more of the entity&apos;s revenues.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_Partner2Member" xlink:to="xoma_Partner2Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_Partner2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Partner 2 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_Partner2Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Partner2 [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_Partner3Member" xlink:type="locator" xlink:label="xoma_Partner3Member" />
    <label xml:lang="en-US" xlink:label="xoma_Partner3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Name or description of a single external partner 3 that accounts for 10 percent or more of the entity&apos;s revenues.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_Partner3Member" xlink:to="xoma_Partner3Member_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_Partner3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Partner 3 [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_Partner3Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Partner3 [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskLineItems" xlink:to="us-gaap_ConcentrationRiskLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk [Line Items]</label>
    <label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Cash equivalents</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfMajorPartners" xlink:type="locator" xlink:label="xoma_NumberOfMajorPartners" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfMajorPartners_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of external partners that accounts for 10 percent or more of an entity&apos;s revenues during the period.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_NumberOfMajorPartners" xlink:to="xoma_NumberOfMajorPartners_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfMajorPartners_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of major partners</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfMajorPartners_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Major Partners</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskPercentage1" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskPercentage1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration risk, percentage (in hundredths)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskPercentage1" xlink:to="us-gaap_ConcentrationRiskPercentage1_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskPercentage1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk Percentage1</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NumberOfOperatingSegments" xlink:type="locator" xlink:label="us-gaap_NumberOfOperatingSegments" />
    <label xml:lang="en-US" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of operating segments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NumberOfOperatingSegments" xlink:to="us-gaap_NumberOfOperatingSegments_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Operating Segments</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Revenues From External Customers And Long Lived Assets [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Revenues From External Customers And Long Lived Assets [Table]</label>
    <loc xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:type="locator" xlink:label="country_US" />
    <label xml:lang="en-US" xlink:label="country_US_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">United States [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="country_US" xlink:to="country_US_lbl" />
    <label xml:lang="en-US" xlink:label="country_US_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">UNITED STATES</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_EuropeMember" xlink:type="locator" xlink:label="srt_EuropeMember" />
    <label xml:lang="en-US" xlink:label="srt_EuropeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Europe [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_EuropeMember" xlink:to="srt_EuropeMember_lbl" />
    <label xml:lang="en-US" xlink:label="srt_EuropeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Europe [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_AsiaPacificMember" xlink:type="locator" xlink:label="srt_AsiaPacificMember" />
    <label xml:lang="en-US" xlink:label="srt_AsiaPacificMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asia Pacific [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_AsiaPacificMember" xlink:to="srt_AsiaPacificMember_lbl" />
    <label xml:lang="en-US" xlink:label="srt_AsiaPacificMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Asia Pacific [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:type="locator" xlink:label="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenues from External Customers and Long-Lived Assets [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_lbl" />
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    <loc xlink:href="xoma-20181231.xsd#xoma_RelatedPartyTransactionsPaymentsToRelatedParty" xlink:type="locator" xlink:label="xoma_RelatedPartyTransactionsPaymentsToRelatedParty" />
    <label xml:lang="en-US" xlink:label="xoma_RelatedPartyTransactionsPaymentsToRelatedParty_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Related party transactions payments to related party.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_RelatedPartyTransactionsPaymentsToRelatedParty" xlink:to="xoma_RelatedPartyTransactionsPaymentsToRelatedParty_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues" xlink:type="locator" xlink:label="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of related party payment on related party gross revenues.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues" xlink:to="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues_lbl" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTable" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTable" />
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsequentEventTable_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Table]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:type="locator" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transactions By Related Party [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:type="locator" xlink:label="us-gaap_RelatedPartyDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_RelatedPartyDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Related Party [Domain]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_CooleyLLPMember" xlink:type="locator" xlink:label="xoma_CooleyLLPMember" />
    <label xml:lang="en-US" xlink:label="xoma_CooleyLLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cooley LLP.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_CooleyLLPMember" xlink:to="xoma_CooleyLLPMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_CooleyLLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cooley [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_CooleyLLPMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cooley L L P [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTypeAxis" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeAxis_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Axis]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTypeDomain" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventTypeDomain_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Domain]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventMember" xlink:type="locator" xlink:label="us-gaap_SubsequentEventMember" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventMember" xlink:to="us-gaap_SubsequentEventMember_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_SubleaseAgreementMember" xlink:type="locator" xlink:label="xoma_SubleaseAgreementMember" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublease agreement.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_SubleaseAgreementMember" xlink:to="xoma_SubleaseAgreementMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease Agreement [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_SubleaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Agreement [Member]</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_BioasisTechnologiesIncMember" xlink:type="locator" xlink:label="xoma_BioasisTechnologiesIncMember" />
    <label xml:lang="en-US" xlink:label="xoma_BioasisTechnologiesIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Bioasis Technologies Inc.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_BioasisTechnologiesIncMember" xlink:to="xoma_BioasisTechnologiesIncMember_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_BioasisTechnologiesIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Bioasis Technologies Inc [Member]</label>
    <label xml:lang="en-US" xlink:label="xoma_BioasisTechnologiesIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Bioasis Technologies Inc [Member]</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:type="locator" xlink:label="us-gaap_SubsequentEventLineItems" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventLineItems_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Line Items]</label>
    <label xml:lang="en-US" xlink:label="xoma_RelatedPartyTransactionsPaymentsToRelatedParty_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payments to related party</label>
    <label xml:lang="en-US" xlink:label="xoma_RelatedPartyTransactionsPaymentsToRelatedParty_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transactions Payments To Related Party</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of related party payment on related party gross revenues</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Related Party Payment On Related Party Gross Revenues</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing" xlink:type="locator" xlink:label="xoma_NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing" />
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    <loc xlink:href="xoma-20181231.xsd#xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing" xlink:type="locator" xlink:label="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing" />
    <label xml:lang="en-US" xlink:label="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Future cash payments upon closing of qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing" xlink:to="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing" xlink:type="locator" xlink:label="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing" />
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional&#8203; cash receipts upon closing&#8203; of qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing" xlink:to="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing" xlink:type="locator" xlink:label="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of net proceeds of each future financing upon closing of the qualified financing.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing" xlink:to="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing_lbl" />
    <label xml:lang="en-US" xlink:label="xoma_NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of future cash payments upon closing of the qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Future Cash Payments Upon Closing Of Qualified Financing</label>
    <label xml:lang="en-US" xlink:label="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Future cash payments upon closing of the qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Future Cash Payments Upon Closing Of Qualified Financing</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of net proceeds of each future financing upon closing of the qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Net Proceeds Of Each Future Financing Upon Closing Of The Qualified Financing</label>
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional cash receipts upon closing of qualified financing</label>
    <label xml:lang="en-US" xlink:label="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Cash Receipts Upon Closing Of Qualified Financing</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements" xlink:type="locator" xlink:label="xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements" />
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of optional royalty rights purchase on future license agreements.</label>
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    <label xml:lang="en-US" xlink:label="xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of Option to purchase royalty right on future license agreements</label>
    <label xml:lang="en-US" xlink:label="xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Optional Royalty Rights Purchase On Future License Agreements</label>
    <label xml:lang="en-US" xlink:label="us-gaap_Revenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total revenues</label>
    <label xml:lang="en-US" xlink:label="xoma_RestructuringChargesCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Restructuring (charge) credit</label>
    <label xml:lang="en-US" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Operating costs and expenses</label>
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:type="locator" xlink:label="us-gaap_NonoperatingIncomeExpense" />
    <label xml:lang="en-US" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other income (expense), net</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NonoperatingIncomeExpense" xlink:to="us-gaap_NonoperatingIncomeExpense_lbl" />
    <label xml:lang="en-US" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nonoperating Income Expense</label>
    <label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Income tax (expense) benefit</label>
    <loc xlink:href="xoma-20181231.xsd#xoma_QuarterlyFinancialInformationLineItems" xlink:type="locator" xlink:label="xoma_QuarterlyFinancialInformationLineItems" />
    <label xml:lang="en-US" xlink:label="xoma_QuarterlyFinancialInformationLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Quarterly financial information.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_QuarterlyFinancialInformationLineItems" xlink:to="xoma_QuarterlyFinancialInformationLineItems_lbl" />
    <loc xlink:href="xoma-20181231.xsd#xoma_QuarterlyFinancialInformationTable" xlink:type="locator" xlink:label="xoma_QuarterlyFinancialInformationTable" />
    <label xml:lang="en-US" xlink:label="xoma_QuarterlyFinancialInformationTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Quarterly financial information.</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="xoma_QuarterlyFinancialInformationTable" xlink:to="xoma_QuarterlyFinancialInformationTable_lbl" />
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