<?xml version="1.0" encoding="us-ascii"?>
<!-- DFS ActiveDisclosure(SM) XBRL Schema Document - http://www.dfsco.com/financial-services/ -->
<!-- Creation Date      : 2019-03-06T08:27:31.6138530+00:00 -->
<!-- Version            : 3.3.6989.14284 -->
<!-- Package ID         : e4f7c612abf244a6aaf4b653cc07da0f -->
<!-- Copyright (c) 2019 Donnelley Financial, LLC. All Rights Reserved. -->
<schema xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:num="http://www.xbrl.org/dtr/type/numeric" xmlns:us-types="http://fasb.org/us-types/2018-01-31" xmlns:stpr="http://xbrl.sec.gov/stpr/2018-01-31" xmlns:srt-types="http://fasb.org/srt-types/2018-01-31" xmlns:naics="http://xbrl.sec.gov/naics/2017-01-31" xmlns:invest="http://xbrl.sec.gov/invest/2013-01-31" xmlns:xoma="http://www.xoma.com/20181231" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:srt="http://fasb.org/srt/2018-01-31" xmlns:us-gaap="http://fasb.org/us-gaap/2018-01-31" xmlns:dei="http://xbrl.sec.gov/dei/2018-01-31" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:country="http://xbrl.sec.gov/country/2017-01-31" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:currency="http://xbrl.sec.gov/currency/2017-01-31" xmlns:exch="http://xbrl.sec.gov/exch/2018-01-31" xmlns:sic="http://xbrl.sec.gov/sic/2011-01-31" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.xoma.com/20181231" xmlns="http://www.w3.org/2001/XMLSchema">
  <import schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/instance" />
  <import schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/linkbase" />
  <import schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" namespace="http://xbrl.org/2005/xbrldt" />
  <import schemaLocation="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd" namespace="http://xbrl.sec.gov/dei/2018-01-31" />
  <import schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd" namespace="http://fasb.org/us-gaap/2018-01-31" />
  <import schemaLocation="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd" namespace="http://fasb.org/srt/2018-01-31" />
  <import schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-types-2018-01-31.xsd" namespace="http://fasb.org/us-types/2018-01-31" />
  <import schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd" namespace="http://www.xbrl.org/dtr/type/numeric" />
  <import schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" namespace="http://www.xbrl.org/dtr/type/non-numeric" />
  <import schemaLocation="http://xbrl.fasb.org/srt/2018/elts/srt-types-2018-01-31.xsd" namespace="http://fasb.org/srt-types/2018-01-31" />
  <import schemaLocation="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd" namespace="http://xbrl.sec.gov/country/2017-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/currency/2017/currency-2017-01-31.xsd" namespace="http://xbrl.sec.gov/currency/2017-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/exch/2018/exch-2018-01-31.xsd" namespace="http://xbrl.sec.gov/exch/2018-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd" namespace="http://xbrl.sec.gov/invest/2013-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/naics/2017/naics-2017-01-31.xsd" namespace="http://xbrl.sec.gov/naics/2017-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/sic/2011/sic-2011-01-31.xsd" namespace="http://xbrl.sec.gov/sic/2011-01-31" />
  <import schemaLocation="https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd" namespace="http://xbrl.sec.gov/stpr/2018-01-31" />
  <annotation>
    <appinfo>
      <link:roleType id="TemplateLink" roleURI="http://www.xoma.com/20181231/role/TemplateLink" xmlns:link="http://www.xbrl.org/2003/linkbase">
        <link:definition>00000 - Document - Template Link</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="xoma-20181231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:title="Calculation Links, all" xlink:type="simple" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="xoma-20181231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:title="Definition Links, all" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="xoma-20181231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:title="Label Links, all" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="xoma-20181231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:title="Presentation Links, all" xlink:type="simple" />
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DocumentDocumentAndEntityInformation" id="Role_DocumentDocumentAndEntityInformation">
        <link:definition>100000 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/StatementCONSOLIDATEDBALANCESHEETS" id="Role_StatementCONSOLIDATEDBALANCESHEETS">
        <link:definition>100010 - Statement - CONSOLIDATED BALANCE SHEETS</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/StatementCONSOLIDATEDBALANCESHEETSParenthetical" id="Role_StatementCONSOLIDATEDBALANCESHEETSParenthetical">
        <link:definition>100020 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/StatementCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSSINCOME" id="Role_StatementCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSSINCOME">
        <link:definition>100030 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS) INCOME</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/StatementCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" id="Role_StatementCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY">
        <link:definition>100040 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS&apos; EQUITY</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/StatementCONSOLIDATEDSTATEMENTSOFCASHFLOWS" id="Role_StatementCONSOLIDATEDSTATEMENTSOFCASHFLOWS">
        <link:definition>100050 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureDescriptionOfBusiness" id="Role_DisclosureDescriptionOfBusiness">
        <link:definition>100060 - Disclosure - Description of Business</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureBasisOfPresentationAndSignificantAccountingPolicies" id="Role_DisclosureBasisOfPresentationAndSignificantAccountingPolicies">
        <link:definition>100070 - Disclosure - Basis of Presentation and Significant Accounting Policies</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementDetail" id="Role_DisclosureConsolidatedFinancialStatementDetail">
        <link:definition>100080 - Disclosure - Consolidated Financial Statement Detail</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLicensingAndOtherArrangements" id="Role_DisclosureLicensingAndOtherArrangements">
        <link:definition>100090 - Disclosure - Licensing and Other Arrangements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureAgenusRoyaltyPurchaseAgreement" id="Role_DisclosureAgenusRoyaltyPurchaseAgreement">
        <link:definition>100100 - Disclosure - Agenus Royalty Purchase Agreement</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurements" id="Role_DisclosureFairValueMeasurements">
        <link:definition>100110 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureDispositions" id="Role_DisclosureDispositions">
        <link:definition>100120 - Disclosure - Dispositions</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureRestructuringCharges" id="Role_DisclosureRestructuringCharges">
        <link:definition>100130 - Disclosure - Restructuring Charges</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancings" id="Role_DisclosureLongTermDebtAndOtherFinancings">
        <link:definition>100140 - Disclosure - Long-Term Debt and Other Financings</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxes" id="Role_DisclosureIncomeTaxes">
        <link:definition>100150 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlans" id="Role_DisclosureCompensationAndOtherBenefitPlans">
        <link:definition>100160 - Disclosure - Compensation and Other Benefit Plans</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureNetLossIncomePerShareAvailableToCommonStockholders" id="Role_DisclosureNetLossIncomePerShareAvailableToCommonStockholders">
        <link:definition>100170 - Disclosure - Net (Loss) Income Per Share Available to Common Stockholders</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStock" id="Role_DisclosureCapitalStock">
        <link:definition>100180 - Disclosure - Capital Stock</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCommitmentsAndContingencies" id="Role_DisclosureCommitmentsAndContingencies">
        <link:definition>100190 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConcentrationOfRiskSegmentAndGeographicInformation" id="Role_DisclosureConcentrationOfRiskSegmentAndGeographicInformation">
        <link:definition>100200 - Disclosure - Concentration of Risk, Segment and Geographic Information</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureSubsequentEvent" id="Role_DisclosureSubsequentEvent">
        <link:definition>100210 - Disclosure - Subsequent Event</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureQuarterlyFinancialInformationUnaudited" id="Role_DisclosureQuarterlyFinancialInformationUnaudited">
        <link:definition>100220 - Disclosure - Quarterly Financial Information (unaudited)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureBasisOfPresentationAndSignificantAccountingPoliciesPolicies" id="Role_DisclosureBasisOfPresentationAndSignificantAccountingPoliciesPolicies">
        <link:definition>100230 - Disclosure - Basis of Presentation and Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementDetailTables" id="Role_DisclosureConsolidatedFinancialStatementDetailTables">
        <link:definition>100240 - Disclosure - Consolidated Financial Statement Detail (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurementsTables" id="Role_DisclosureFairValueMeasurementsTables">
        <link:definition>100250 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsTables" id="Role_DisclosureLongTermDebtAndOtherFinancingsTables">
        <link:definition>100260 - Disclosure - Long-Term Debt and Other Financings (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesTables" id="Role_DisclosureIncomeTaxesTables">
        <link:definition>100270 - Disclosure - Income Taxes (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansTables" id="Role_DisclosureCompensationAndOtherBenefitPlansTables">
        <link:definition>100280 - Disclosure - Compensation and Other Benefit Plans (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureNetLossIncomePerShareAvailableToCommonStockholdersTables" id="Role_DisclosureNetLossIncomePerShareAvailableToCommonStockholdersTables">
        <link:definition>100290 - Disclosure - Net (Loss) Income Per Share Available to Common Stockholders (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockTables" id="Role_DisclosureCapitalStockTables">
        <link:definition>100300 - Disclosure - Capital Stock (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCommitmentsAndContingenciesTables" id="Role_DisclosureCommitmentsAndContingenciesTables">
        <link:definition>100310 - Disclosure - Commitments and Contingencies (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConcentrationOfRiskSegmentAndGeographicInformationTables" id="Role_DisclosureConcentrationOfRiskSegmentAndGeographicInformationTables">
        <link:definition>100320 - Disclosure - Concentration of Risk, Segment and Geographic Information (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureQuarterlyFinancialInformationUnauditedTables" id="Role_DisclosureQuarterlyFinancialInformationUnauditedTables">
        <link:definition>100330 - Disclosure - Quarterly Financial Information (unaudited) (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureBasisOfPresentationAndSignificantAccountingPoliciesAdditionalInformationDetails" id="Role_DisclosureBasisOfPresentationAndSignificantAccountingPoliciesAdditionalInformationDetails">
        <link:definition>100340 - Disclosure - Basis of Presentation and Significant Accounting Policies - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementDetailAdditionalInformation1Details" id="Role_DisclosureConsolidatedFinancialStatementDetailAdditionalInformation1Details">
        <link:definition>100350 - Disclosure - Consolidated Financial Statement Detail - Additional Information 1 (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementsDetailAdditionalInformation2Details" id="Role_DisclosureConsolidatedFinancialStatementsDetailAdditionalInformation2Details">
        <link:definition>100360 - Disclosure - Consolidated Financial Statements Detail - Additional Information 2 (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementDetailPropertyAndEquipmentNetDetails" id="Role_DisclosureConsolidatedFinancialStatementDetailPropertyAndEquipmentNetDetails">
        <link:definition>100370 - Disclosure - Consolidated Financial Statement Detail - Property and Equipment, Net (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementsDetailAdditionalInformation3Details" id="Role_DisclosureConsolidatedFinancialStatementsDetailAdditionalInformation3Details">
        <link:definition>100380 - Disclosure - Consolidated Financial Statements Detail - Additional Information 3 (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConsolidatedFinancialStatementsDetailAccruedAndOtherLiabilitiesDetails" id="Role_DisclosureConsolidatedFinancialStatementsDetailAccruedAndOtherLiabilitiesDetails">
        <link:definition>100390 - Disclosure - Consolidated Financial Statements Detail - Accrued and Other Liabilities (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLicensingAndOtherArrangementsNovartisAdditionalInformationDetails" id="Role_DisclosureLicensingAndOtherArrangementsNovartisAdditionalInformationDetails">
        <link:definition>100400 - Disclosure - Licensing and Other Arrangements - Novartis - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLicensingAndOtherArrangementsRezoluteAdditionalInformationDetails" id="Role_DisclosureLicensingAndOtherArrangementsRezoluteAdditionalInformationDetails">
        <link:definition>100410 - Disclosure - Licensing and Other Arrangements - Rezolute - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLicensingAndOtherArrangementsNIAIDAdditionalInformationDetails" id="Role_DisclosureLicensingAndOtherArrangementsNIAIDAdditionalInformationDetails">
        <link:definition>100420 - Disclosure - Licensing and Other Arrangements - NIAID - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLicensingAndOtherArrangementsSaleOfFutureRevenueStreamsAdditionalInformationDetails" id="Role_DisclosureLicensingAndOtherArrangementsSaleOfFutureRevenueStreamsAdditionalInformationDetails">
        <link:definition>100430 - Disclosure - Licensing and Other Arrangements - Sale of Future Revenue Streams - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureAgenusRoyaltyPurchaseAgreementDetails" id="Role_DisclosureAgenusRoyaltyPurchaseAgreementDetails">
        <link:definition>100440 - Disclosure - Agenus Royalty Purchase Agreement (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurementsFinancialAssetsAndLiabilitiesCarriedAtFairValueOnRecurringBasisDetails" id="Role_DisclosureFairValueMeasurementsFinancialAssetsAndLiabilitiesCarriedAtFairValueOnRecurringBasisDetails">
        <link:definition>100450 - Disclosure - Fair Value Measurements - Financial Assets and Liabilities Carried at Fair Value on Recurring Basis (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfChangesInEstimatedFairValueOfLevel3FinancialAssetsDetails" id="Role_DisclosureFairValueMeasurementsSummaryOfChangesInEstimatedFairValueOfLevel3FinancialAssetsDetails">
        <link:definition>100460 - Disclosure - Fair Value Measurements - Summary of Changes In Estimated Fair Value of Level 3 Financial Assets (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurementsEstimatedFairValueOfEquitySecuritiesAssumptionsDetails" id="Role_DisclosureFairValueMeasurementsEstimatedFairValueOfEquitySecuritiesAssumptionsDetails">
        <link:definition>100470 - Disclosure - Fair Value Measurements - Estimated Fair Value of Equity Securities Assumptions (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureFairValueMeasurementsOutstandingLongTermDebtCarryingAmountAndEstimatedFairValueDetails" id="Role_DisclosureFairValueMeasurementsOutstandingLongTermDebtCarryingAmountAndEstimatedFairValueDetails">
        <link:definition>100480 - Disclosure - Fair Value Measurements - Outstanding Long Term Debt Carrying Amount and Estimated Fair Value (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureDispositionsAdditionalInformationDetails" id="Role_DisclosureDispositionsAdditionalInformationDetails">
        <link:definition>100490 - Disclosure - Dispositions - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureRestructuringChargesAdditionalInformationDetails" id="Role_DisclosureRestructuringChargesAdditionalInformationDetails">
        <link:definition>100500 - Disclosure - Restructuring Charges - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsSiliconValleyBankLoanAgreementAdditionalInformationDetails" id="Role_DisclosureLongTermDebtAndOtherFinancingsSiliconValleyBankLoanAgreementAdditionalInformationDetails">
        <link:definition>100510 - Disclosure - Long-Term Debt and Other Financings - Silicon Valley Bank Loan Agreement - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsNovartisNoteAdditionalInformationDetails" id="Role_DisclosureLongTermDebtAndOtherFinancingsNovartisNoteAdditionalInformationDetails">
        <link:definition>100520 - Disclosure - Long-Term Debt and Other Financings - Novartis Note - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsServierLoanAgreementAdditionalInformationDetails" id="Role_DisclosureLongTermDebtAndOtherFinancingsServierLoanAgreementAdditionalInformationDetails">
        <link:definition>100530 - Disclosure - Long-Term Debt and Other Financings - Servier Loan Agreement - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsHerculesTermLoanAdditionalInformationDetails" id="Role_DisclosureLongTermDebtAndOtherFinancingsHerculesTermLoanAdditionalInformationDetails">
        <link:definition>100540 - Disclosure - Long-Term Debt and Other Financings - Hercules Term Loan - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureLongTermDebtAndOtherFinancingsInterestExpenseAndAmortizationOfDebtIssuanceCostsDetails" id="Role_DisclosureLongTermDebtAndOtherFinancingsInterestExpenseAndAmortizationOfDebtIssuanceCostsDetails">
        <link:definition>100550 - Disclosure - Long-Term Debt and Other Financings - Interest Expense and Amortization of Debt Issuance Costs (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails" id="Role_DisclosureIncomeTaxesAdditionalInformationDetails">
        <link:definition>100560 - Disclosure - Income Taxes - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesScheduleOfProvisionForIncomeTaxesAllCurrentDetails" id="Role_DisclosureIncomeTaxesScheduleOfProvisionForIncomeTaxesAllCurrentDetails">
        <link:definition>100570 - Disclosure - Income Taxes - Schedule of Provision for Income Taxes (All Current) (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesReconciliationBetweenTaxProvisionComputedAtFederalStatutoryIncomeTaxRateAndActualEffectiveIncomeTaxRateDetails" id="Role_DisclosureIncomeTaxesReconciliationBetweenTaxProvisionComputedAtFederalStatutoryIncomeTaxRateAndActualEffectiveIncomeTaxRateDetails">
        <link:definition>100580 - Disclosure - Income Taxes - Reconciliation Between the Tax Provision Computed at the Federal Statutory Income Tax Rate and Actual Effective Income Tax Rate (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesComponentsOfNetDeferredTaxAssetsDetails" id="Role_DisclosureIncomeTaxesComponentsOfNetDeferredTaxAssetsDetails">
        <link:definition>100590 - Disclosure - Income Taxes - Components of Net Deferred Tax Assets (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureIncomeTaxesScheduleOfUnrecognizedTaxBenefitsDetails" id="Role_DisclosureIncomeTaxesScheduleOfUnrecognizedTaxBenefitsDetails">
        <link:definition>100600 - Disclosure - Income Taxes - Schedule of Unrecognized Tax Benefits (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansAdditionalInformationDetails" id="Role_DisclosureCompensationAndOtherBenefitPlansAdditionalInformationDetails">
        <link:definition>100610 - Disclosure - Compensation and Other Benefit Plans - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansStockOptionActivityDetails" id="Role_DisclosureCompensationAndOtherBenefitPlansStockOptionActivityDetails">
        <link:definition>100620 - Disclosure - Compensation and Other Benefit Plans - Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansUnvestedRSUActivityDetails" id="Role_DisclosureCompensationAndOtherBenefitPlansUnvestedRSUActivityDetails">
        <link:definition>100630 - Disclosure - Compensation and Other Benefit Plans - Unvested RSU Activity (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansWeightedAverageAssumptionsDetails" id="Role_DisclosureCompensationAndOtherBenefitPlansWeightedAverageAssumptionsDetails">
        <link:definition>100640 - Disclosure - Compensation and Other Benefit Plans - Weighted Average Assumptions (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCompensationAndOtherBenefitPlansStockBasedCompensationExpenseDetails" id="Role_DisclosureCompensationAndOtherBenefitPlansStockBasedCompensationExpenseDetails">
        <link:definition>100650 - Disclosure - Compensation and Other Benefit Plans - Stock-based Compensation Expense (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureNetLossIncomePerShareAvailableToCommonStockholdersOutstandingSecuritiesConsideredAntiDilutiveDetails" id="Role_DisclosureNetLossIncomePerShareAvailableToCommonStockholdersOutstandingSecuritiesConsideredAntiDilutiveDetails">
        <link:definition>100660 - Disclosure - Net (Loss) Income Per Share Available to Common Stockholders - Outstanding Securities Considered Anti-Dilutive (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureNetLossIncomePerShareAvailableToCommonStockholdersReconciliationOfNumeratorAndDenominatorUsedInCalculationOfBasicAndDilutedNetIncomeLossPerShareAvailableToCommonStockholdersDetails" id="Role_DisclosureNetLossIncomePerShareAvailableToCommonStockholdersReconciliationOfNumeratorAndDenominatorUsedInCalculationOfBasicAndDilutedNetIncomeLossPerShareAvailableToCommonStockholdersDetails">
        <link:definition>100670 - Disclosure - Net (Loss) Income Per Share Available to Common Stockholders - Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income (Loss) per Share Available to Common Stockholders (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockRightsOfferring2018AdditionalInformationDetails" id="Role_DisclosureCapitalStockRightsOfferring2018AdditionalInformationDetails">
        <link:definition>100680 - Disclosure - Capital Stock - Rights Offerring 2018 - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockBiotechnologyValueFundFinancing2017AdditionalInformationDetails" id="Role_DisclosureCapitalStockBiotechnologyValueFundFinancing2017AdditionalInformationDetails">
        <link:definition>100690 - Disclosure - Capital Stock - Biotechnology Value Fund Financing 2017 - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockATMAgreementsAdditionalInformationDetails" id="Role_DisclosureCapitalStockATMAgreementsAdditionalInformationDetails">
        <link:definition>100700 - Disclosure - Capital Stock - ATM Agreements - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockCommonStockPurchaseAgreementAdditionalInformationDetails" id="Role_DisclosureCapitalStockCommonStockPurchaseAgreementAdditionalInformationDetails">
        <link:definition>100710 - Disclosure - Capital Stock - Common Stock Purchase Agreement - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockSummaryOfCommonStockWarrantsOutstandingDetails" id="Role_DisclosureCapitalStockSummaryOfCommonStockWarrantsOutstandingDetails">
        <link:definition>100720 - Disclosure - Capital Stock - Summary of Common Stock Warrants Outstanding (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCapitalStockCommonStockWarrantsAdditionalInformationDetails" id="Role_DisclosureCapitalStockCommonStockWarrantsAdditionalInformationDetails">
        <link:definition>100730 - Disclosure - Capital Stock - Common Stock Warrants - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails" id="Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails">
        <link:definition>100740 - Disclosure - Commitments and Contingencies - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureCommitmentsAndContingenciesFutureMinimumLeaseCommitmentsDetails" id="Role_DisclosureCommitmentsAndContingenciesFutureMinimumLeaseCommitmentsDetails">
        <link:definition>100750 - Disclosure - Commitments and Contingencies - Future Minimum Lease Commitments (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConcentrationOfRiskSegmentAndGeographicInformationAdditionalInformation1Details" id="Role_DisclosureConcentrationOfRiskSegmentAndGeographicInformationAdditionalInformation1Details">
        <link:definition>100760 - Disclosure - Concentration of Risk, Segment and Geographic Information - Additional Information 1 (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConcentrationOfRiskSegmentAndGeographicInformationAdditionalInformation2Details" id="Role_DisclosureConcentrationOfRiskSegmentAndGeographicInformationAdditionalInformation2Details">
        <link:definition>100770 - Disclosure - Concentration of Risk, Segment and Geographic Information - Additional Information 2 (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureConcentrationOfRiskSegmentAndGeographicInformationRevenueByGeographicalRegionDetails" id="Role_DisclosureConcentrationOfRiskSegmentAndGeographicInformationRevenueByGeographicalRegionDetails">
        <link:definition>100780 - Disclosure - Concentration of Risk, Segment and Geographic Information - Revenue by Geographical Region (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureSubsequentEventAdditionalInformationDetails" id="Role_DisclosureSubsequentEventAdditionalInformationDetails">
        <link:definition>100790 - Disclosure - Subsequent Event - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureQuarterlyFinancialInformationUnauditedDetails" id="Role_DisclosureQuarterlyFinancialInformationUnauditedDetails">
        <link:definition>100800 - Disclosure - Quarterly Financial Information (unaudited) (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.xoma.com/20181231/taxonomy/role/DisclosureQuarterlyFinancialInformationUnauditedParentheticalDetails" id="Role_DisclosureQuarterlyFinancialInformationUnauditedParentheticalDetails">
        <link:definition>100810 - Disclosure - Quarterly Financial Information (unaudited) (Parenthetical) (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </appinfo>
  </annotation>
  <element id="xoma_RestructuringChargesCredits" name="RestructuringChargesCredits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LongTermRoyaltyReceivableNonCurrent" name="LongTermRoyaltyReceivableNonCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_EquitySecuritiesFvNiNonCurrent" name="EquitySecuritiesFvNiNonCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AccruedAndOtherLiabilitiesCurrent" name="AccruedAndOtherLiabilitiesCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_RevenueRecognizeUnderUnitsOfRevenueMethod" name="RevenueRecognizeUnderUnitsOfRevenueMethod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_SharesReleasedOfRestrictedStockUnits" name="SharesReleasedOfRestrictedStockUnits" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ReleaseOfRestrictedStockUnits" name="ReleaseOfRestrictedStockUnits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PreferredStockIssuedDuringPeriodSharesNewIssues" name="PreferredStockIssuedDuringPeriodSharesNewIssues" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_PreferredStockIssuedDuringPeriodValueNewIssues" name="PreferredStockIssuedDuringPeriodValueNewIssues" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement" name="FairValueOfCommonStockSharesReceivedAsConsiderationForLicenseAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan" name="LicenseFeeRecognizedRelatedToRepaymentOfPrincipalAndAccruedInterestUnderLoan" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims" name="DefinedContributionPlanIssuanceOfCommonStockForServicesOrClaims" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_GainLossOnSublease" name="GainLossOnSublease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod" name="IncreaseDecreaseInUnearnedRevenueRecognizedUnderUnitsOfRevenueMethod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement" name="PurchaseOfRoyaltyRightsInConnectionWithPurchaseAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_EndOfTermFeePaidToLender" name="EndOfTermFeePaidToLender" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan" name="NonCashOrPartNoncashExchangeOfPrincipalAndAccruedInterestUnderServierLoan" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_InterestAddedPrincipalBalancesLongTermDebt" name="InterestAddedPrincipalBalancesLongTermDebt" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_AccruedCostRelatedToIssuanceOfPreferredAndCommonStock" name="AccruedCostRelatedToIssuanceOfPreferredAndCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_PrepaidFinancingCostRelatedToIssuanceOfCommonStock" name="PrepaidFinancingCostRelatedToIssuanceOfCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_IssuanceOfCommonStockWarrant" name="IssuanceOfCommonStockWarrant" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_DescriptionOfBusinessAbstract" name="DescriptionOfBusinessAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ConsolidatedFinancialStatementDetailAbstract" name="ConsolidatedFinancialStatementDetailAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LicensingAndOtherArrangementsTextBlock" name="LicensingAndOtherArrangementsTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_LicensingAndOtherArrangementsAbstract" name="LicensingAndOtherArrangementsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RoyaltyPurchaseAgreementTextBlock" name="RoyaltyPurchaseAgreementTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RoyaltyPurchaseAgreementAbstract" name="RoyaltyPurchaseAgreementAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_DispositionsDisclosureTextBlock" name="DispositionsDisclosureTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DispositionsAbstract" name="DispositionsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ConcentrationOfRiskSegmentAndGeographicInformationAbstract" name="ConcentrationOfRiskSegmentAndGeographicInformationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LiquidityAndFinancialConditionPolicyTextBlock" name="LiquidityAndFinancialConditionPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RevenueRecognitionDeferredRevenuePolicyTextBlock" name="RevenueRecognitionDeferredRevenuePolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RestructuringAndImpairmentChargesPolicyTextBlock" name="RestructuringAndImpairmentChargesPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_EquitySecuritiesPolicy" name="EquitySecuritiesPolicy" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_FutureMilestonesAndRoyaltiesPurchaseRightsPolicyPolicyTextBlock" name="FutureMilestonesAndRoyaltiesPurchaseRightsPolicyPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_StockWarrantsPolicyPolicyTextBlock" name="StockWarrantsPolicyPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_FairValueAssetsMeasuredOnEstimatedFairValueOfEquitySecuritiesAssumptionsTableTextBlock" name="FairValueAssetsMeasuredOnEstimatedFairValueOfEquitySecuritiesAssumptionsTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_InterestExpenseAndAmortizationOfDebtIssuanceCostsAndDiscountsTableTextBlock" name="InterestExpenseAndAmortizationOfDebtIssuanceCostsAndDiscountsTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_BasisOfPresentationAndSignificantAccountingPoliciesLineItems" name="BasisOfPresentationAndSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_BasisOfPresentationAndSignificantAccountingPoliciesTable" name="BasisOfPresentationAndSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ImpairmentOfLongTermRoyaltyReceivable" name="ImpairmentOfLongTermRoyaltyReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_LongTermEquitySecuritiesLineItems" name="LongTermEquitySecuritiesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RezoluteIncMember" name="RezoluteIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_EquipmentAndFurnitureGross" name="EquipmentAndFurnitureGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_EquipmentSoldAndDisposedDuringPeriod" name="EquipmentSoldAndDisposedDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AccruedRestructuringCostsCurrent" name="AccruedRestructuringCostsCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_AccruedIncentiveCompensation" name="AccruedIncentiveCompensation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_LiabilityRelatedToSublease" name="LiabilityRelatedToSublease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_LicenseAgreementConsiderationReceived" name="LicenseAgreementConsiderationReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_ProceedsFromUpfrontPayment" name="ProceedsFromUpfrontPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AggregateFairValueOfCommonStock" name="AggregateFairValueOfCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_CommonStockPremium" name="CommonStockPremium" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones" name="EligibleMilestonePaymentsReceivableUponAchievementOfDevelopmentRegulatoryAndCommercialMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_ClosingStockPricePerShare" name="ClosingStockPricePerShare" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_NovartisPharmaAGMember" name="NovartisPharmaAGMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_XOMA052LicenseAgreementMember" name="XOMA052LicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_IL1TargetLicenseAgreementMember" name="IL1TargetLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LesLaboratoriesServierMember" name="LesLaboratoriesServierMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember" name="LicensesAndRelatedMaterialsProcessAndKnowHowAndFilingsToRegulatoryAuthorityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LicenseAgreementMember" name="LicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NovartisInternationalPharmaceuticalLtdMember" name="NovartisInternationalPharmaceuticalLtdMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NumberOfLicenseAgreements" name="NumberOfLicenseAgreements" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_AgreementTerminationPriorWrittenNoticePeriod" name="AgreementTerminationPriorWrittenNoticePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_NumberOfPerformanceObligations" name="NumberOfPerformanceObligations" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_LicenseAgreementTransactionPrice" name="LicenseAgreementTransactionPrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer" name="RevenueRecognitionMultiplePerformanceObligationsContractWithCustomer" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_AgreementTerminationNoticePeriod" name="AgreementTerminationNoticePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_UpfrontPaymentRecognizedAsRevenue" name="UpfrontPaymentRecognizedAsRevenue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_MilestoneReceivedUnderCollaborationAgreement" name="MilestoneReceivedUnderCollaborationAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum" name="CollaborativeArrangementContingentConsiderationPotentialCashPaymentMaximum" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_UpfrontOptionPayment" name="UpfrontOptionPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_CollaborativeLicensingAndOtherArrangementsAbstract" name="CollaborativeLicensingAndOtherArrangementsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AmendedCommonStockPurchaseAgreementMember" name="AmendedCommonStockPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_InitialClosingMember" name="InitialClosingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_QualifiedFinancingMember" name="QualifiedFinancingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TwoThousandNineteenClosingMember" name="TwoThousandNineteenClosingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_CommonStockPurchaseAgreementMember" name="CommonStockPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_InterimFinancingClosingMember" name="InterimFinancingClosingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember" name="AmendedLicenseAgreementAndAmendedCommonStockPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember" name="LicensesAndRelatedMaterialsProductDataOrFilingProcessAndKnowHowMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_EligibleToReceiveInCash" name="EligibleToReceiveInCash" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_EligibleToReceiveCommonStockRelatedToFinancingActivities" name="EligibleToReceiveCommonStockRelatedToFinancingActivities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_GrossProceedsFromQualifiedFinancing" name="GrossProceedsFromQualifiedFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AdditionalCommonStockReceiveForQualifiedFinancing" name="AdditionalCommonStockReceiveForQualifiedFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_CommonStockThresholdTradingDays" name="CommonStockThresholdTradingDays" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_EligibleToReceiveInOrderToMaintainLicenseAgreement" name="EligibleToReceiveInOrderToMaintainLicenseAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_PercentageOfAggregateSharesHeldForFutureIssuance" name="PercentageOfAggregateSharesHeldForFutureIssuance" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_CommonStockPurchaseAgreementDescription" name="CommonStockPurchaseAgreementDescription" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_CommonStockValueReceivable" name="CommonStockValueReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_CommonStockSharesReceivable" name="CommonStockSharesReceivable" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_SharesReceived" name="SharesReceived" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_CashReceived" name="CashReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_ReimbursableTechnologyTransferExpensesReceived" name="ReimbursableTechnologyTransferExpensesReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_UpfrontConsiderationToIncrementalDiscountForFuturePayment" name="UpfrontConsiderationToIncrementalDiscountForFuturePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_SharesReceivedValue" name="SharesReceivedValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" name="ContractWithCustomerLiabilityMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_MaximumRevenueFromContract" name="MaximumRevenueFromContract" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_ContractualTerm" name="ContractualTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ContractsRevenueWroteOff" name="ContractsRevenueWroteOff" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_DeferredRevenueArrangementNameOfParty2Member" name="DeferredRevenueArrangementNameOfParty2Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency2Member" name="NonsoftwareLicenseArrangementWithGovernmentalAgency2Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NonsoftwareLicenseArrangementWithGovernmentalAgency3Member" name="NonsoftwareLicenseArrangementWithGovernmentalAgency3Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones" name="EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_NumberOfRoyaltyInterestAcquisitionAgreements" name="NumberOfRoyaltyInterestAcquisitionAgreements" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember" name="HealthCareRoyaltyPartnersTwoLimitedPartnersMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_FirstRoyaltyInterestAcquisitionAgreementMember" name="FirstRoyaltyInterestAcquisitionAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SecondRoyaltyInterestAcquisitionAgreementMember" name="SecondRoyaltyInterestAcquisitionAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RevenueRecognizedUnderUnitsOfRevenueMethod" name="RevenueRecognizedUnderUnitsOfRevenueMethod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts" name="PurchasedPercentageOfRoyaltiesOnNetSalesOfProducts" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_PurchasedPercentageOfMilestones" name="PurchasedPercentageOfMilestones" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased" name="NumberOfLicensedProductsRelatedToMilestonesAndRoyaltiesPurchased" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones" name="PurchasedEligibleMilestonePaymentsReceivableUponAchievementOfPotentialDevelopmentRegulatoryAndCommercialMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_RoyaltyPurchaseAgreementLineItems" name="RoyaltyPurchaseAgreementLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RoyaltyPurchaseAgreementTable" name="RoyaltyPurchaseAgreementTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RoyaltyPurchaseAgreementMember" name="RoyaltyPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AgenusIncMember" name="AgenusIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember" name="RightToReceiveLowSingleToMidTeenDigitRoyaltiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RightToReceiveLowSingleDigitRoyaltiesMember" name="RightToReceiveLowSingleDigitRoyaltiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_IncyteEuropeSarlMember" name="IncyteEuropeSarlMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_MerckSharpAndDohmeCorporationMember" name="MerckSharpAndDohmeCorporationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember" name="IncyteEuropeSarlAndMerckSharpAndDohmeCorporationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SiliconValleyBankMember" name="SiliconValleyBankMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_PaymentsToAcquireMilestonesAndRoyalties" name="PaymentsToAcquireMilestonesAndRoyalties" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_LoanBorrowed" name="LoanBorrowed" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLongTermEquitySecuritiesAtContractInception" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLongTermEquitySecuritiesAtContractInception" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_EquitySecuritiesFvNiTerm" name="EquitySecuritiesFvNiTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_MeasurementInputLiquidityOfSharesMember" name="MeasurementInputLiquidityOfSharesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_MeasurementInputLiquidationMember" name="MeasurementInputLiquidationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_MeasurementInputNearTermSaleMember" name="MeasurementInputNearTermSaleMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_MeasurementInputNearTermFinancingMember" name="MeasurementInputNearTermFinancingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NovartisNoteMember" name="NovartisNoteMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ContingentPayment" name="ContingentPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive" name="SalesOfBusinessNumberOfCommonStockSharesEligibleToReceive" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RoyaltyReceivablePercentageOnNetSales" name="RoyaltyReceivablePercentageOnNetSales" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_BiodefenseBusinessMember" name="BiodefenseBusinessMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember" name="AssetPurchaseAgreementAndOlogyBioservicesLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement" name="CancellationOfIssuanceOfCommonStockUnderPurchaseAgreement" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives" name="ContingentPaymentUponAchievingCertainSpecifiedFutureOperatingObjectives" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_MilestonePaymentEarned" name="MilestonePaymentEarned" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_AmountReceivedFromSaleOfDiscontinuedOperation" name="AmountReceivedFromSaleOfDiscontinuedOperation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_RestructuringAndRelatedCostNumberOfEmployeesTerminated" name="RestructuringAndRelatedCostNumberOfEmployeesTerminated" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_TwoThousandSixteenRestructuringMember" name="TwoThousandSixteenRestructuringMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TwoThousandSeventeenRestructuringMember" name="TwoThousandSeventeenRestructuringMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember" name="TwoThousandSeventeenAndTwoThousandSixteenRestructuringMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LeaseRelatedCostsMember" name="LeaseRelatedCostsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AccruedAndOtherLiabilitiesMember" name="AccruedAndOtherLiabilitiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_RestructuringReversalOfDeferredRentLiabilities" name="RestructuringReversalOfDeferredRentLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_OperatingLeasesNumberOfSubtenants" name="OperatingLeasesNumberOfSubtenants" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DebtInstrumentMaximumBorrowingCapacity" name="DebtInstrumentMaximumBorrowingCapacity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_IncreaseInDebtInstrumentBorrowingCapacity" name="IncreaseInDebtInstrumentBorrowingCapacity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_EarlierEffectiveDateOfTermLoan" name="EarlierEffectiveDateOfTermLoan" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_EffectiveDateOfTermLoanExtended" name="EffectiveDateOfTermLoanExtended" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_GrossCashProceedsReceivedFromMilestoneAndLicensingPayments" name="GrossCashProceedsReceivedFromMilestoneAndLicensingPayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_LoanAndSecurityAgreementMember" name="LoanAndSecurityAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TermLoanMember" name="TermLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NovartisMember" name="NovartisMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_FirstAnniversaryMember" name="FirstAnniversaryMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SecondAnniversaryMember" name="SecondAnniversaryMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_PeriodOfMonthlyPaymentsOfPrincipalAndInterest" name="PeriodOfMonthlyPaymentsOfPrincipalAndInterest" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DaysOfPeriodInterest" name="DaysOfPeriodInterest" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DebtInstrumentMaturityDays" name="DebtInstrumentMaturityDays" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RepaymentOfTermLoan" name="RepaymentOfTermLoan" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PercentageOfPrepaymentFee" name="PercentageOfPrepaymentFee" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_PercentageOfAdditionalInterestRateOfOutstandingLoan" name="PercentageOfAdditionalInterestRateOfOutstandingLoan" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ExercisablePeriodOfWarrants" name="ExercisablePeriodOfWarrants" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_UnamortizedAmountOfDeferredCharges" name="UnamortizedAmountOfDeferredCharges" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum" name="CollaborativeArrangementResearchAndDevelopmentExpenseFundedThroughDebtInstrumentPercentageMaximum" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_NovartisNoteAmendmentMember" name="NovartisNoteAmendmentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_DateOfAgreement" name="DateOfAgreement" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DebtInstrumentBorrowingCapacity" name="DebtInstrumentBorrowingCapacity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_ServierLoanMember" name="ServierLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_PaymentOfDebtThroughCashByCollaborator" name="PaymentOfDebtThroughCashByCollaborator" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PercentageOfPrepaymentChargeOnDebt" name="PercentageOfPrepaymentChargeOnDebt" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_HerculesTermLoanMember" name="HerculesTermLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ClassOfWarrantOrRightExpirationYearAndMonth" name="ClassOfWarrantOrRightExpirationYearAndMonth" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_HerculesLoanMember" name="HerculesLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_OtherFinancingsMember" name="OtherFinancingsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_FederalOrphanCreditMember" name="FederalOrphanCreditMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_EffectiveIncomeTaxRateReconciliationStockCompensationAndOtherPermanentDifferencesPercent" name="EffectiveIncomeTaxRateReconciliationStockCompensationAndOtherPermanentDifferencesPercent" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_NetOperatingLossCarryforwardsExpirationYear" name="NetOperatingLossCarryforwardsExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_TaxCreditCarryforwardExpirationYear" name="TaxCreditCarryforwardExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage" name="OperatingLossCarryforwardsOffsetOfTaxableIncomePercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions" name="UnrecognizedTaxBenefitsIncreasesDecreasesResultingFromPriorPeriodTaxPositions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_TwoThousandFifteenEmployeeStockPurchasePlanMember" name="TwoThousandFifteenEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TwoThousandTenLongTermIncentiveAndStockAwardPlanMember" name="TwoThousandTenLongTermIncentiveAndStockAwardPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_IncentiveStockOptionsMember" name="IncentiveStockOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_OptionsAndStockAppreciationRightsMember" name="OptionsAndStockAppreciationRightsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_OtherTypesOfStockAwardsMember" name="OtherTypesOfStockAwardsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LongTermIncentivePlanMember" name="LongTermIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NonExecutiveEmployeeMember" name="NonExecutiveEmployeeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ServiceBasedStockOptionsMember" name="ServiceBasedStockOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions" name="PercentageOfCompensationOfEligibleEmployeesToPurchaseSharesOfEntityCommonStockAtDiscountThroughPayrollDeductions" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount" name="DefinedContributionPlanMaximumAnnualContributionPerEmployeeOver50YearsOldAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum" name="DefinedContributionPlanAgeRequiredForCatchUpContributionMinimum" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum" name="DefinedContributionPlanEmployerMatchingContributionPercentOfEmployerSalaryDeferredMaximum" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage" name="DefinedContributionPlanCostRecognizedAndPaidThroughIssuanceOfCommonSharesPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodDescription" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedUponExerciseOfOptionsAndRSUsOutstanding" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAgeRequiredForImmediateVestingOfRsus" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPeriodForRetirementAge" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantDateFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_CommonStockOptionsAndRestrictedStockUnitsMember" name="CommonStockOptionsAndRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_DeemedDividendsOnConvertiblePreferredStock" name="DeemedDividendsOnConvertiblePreferredStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfStockOptions" name="IncrementalCommonSharesAttributableToDilutiveEffectOfStockOptions" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_IncrementalCommonSharesAttributableToDilutiveEffectOfWarrants" name="IncrementalCommonSharesAttributableToDilutiveEffectOfWarrants" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_NetIncomeLossAvailableToCommonStockholdersBasicAndDilutedAbstract" name="NetIncomeLossAvailableToCommonStockholdersBasicAndDilutedAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_WriteOffOfCapitalizedOfferingCost" name="WriteOffOfCapitalizedOfferingCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock" name="GrossProceedsFromIssuanceOfCcommonStockAndPreferredStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_RightsOfferingAmount" name="RightsOfferingAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_SeriesXPreferredStockMember" name="SeriesXPreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SeriesYPreferredStockMember" name="SeriesYPreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SeriesYConvertiblePreferredStockMember" name="SeriesYConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SeriesXAndSeriesYConvertiblePreferredStockMember" name="SeriesXAndSeriesYConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_BiotechnologyValueFundLPMember" name="BiotechnologyValueFundLPMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_PreferredStockConversionPricePerShare" name="PreferredStockConversionPricePerShare" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_ConvertibleCommonStockSharesIssuedUponConversion" name="ConvertibleCommonStockSharesIssuedUponConversion" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_PercentageOfPreferredStockConversionBlockerProvision" name="PercentageOfPreferredStockConversionBlockerProvision" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock" name="MinorityInterestOwnershipPercentageAfterConversionOfConvertiblePreferredStock" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_SeriesXConvertiblePreferredStockMember" name="SeriesXConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember" name="BiotechnologyValueFundLPAndCertainOfItsAffiliatesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock" name="FairValueOfCommonStockAmountExceededAllocatedPurchasePriceOfConvertiblePreferredStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued" name="AtMarketIssuanceSalesAgreementMaximumValueOfCommonStockToBeIssued" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares" name="PercentageOfGrossProceedsPaidToAgentForSaleOfCommonShares" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_TwoThousandEighteenAtMarketAgreementMember" name="TwoThousandEighteenAtMarketAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AtmAgreement4Member" name="AtmAgreement4Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_AgreementExpirationDate" name="AgreementExpirationDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_IssuanceDateOfCommonStockWarrants" name="IssuanceDateOfCommonStockWarrants" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_CommonStockWarrantsExpirationDate" name="CommonStockWarrantsExpirationDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_FiveYearWarrantsIssuedFirstRangeMember" name="FiveYearWarrantsIssuedFirstRangeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_FiveYearWarrantsIssuedSecondRangeMember" name="FiveYearWarrantsIssuedSecondRangeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_TenYearWarrantsIssuedThirdRangeMember" name="TenYearWarrantsIssuedThirdRangeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_StockholdersEquityMember" name="StockholdersEquityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ThirdPartyConsultantMember" name="ThirdPartyConsultantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_ContractualObligationEstimatedMilestonePayments" name="ContractualObligationEstimatedMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_CommitmentsAndContingenciesLineItems" name="CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_CommitmentsAndContingenciesTable" name="CommitmentsAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember" name="LeaseAgreementCommencedInSeptembrTwoThousandAndSeventeenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember" name="SubleaseAgreementCommencedOnDecemberTwentySixTwoThousandAndSeventeenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember" name="SubleaseAgreementCommencedOnMayOneTwoThousandAndEighteenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember" name="SubleaseAgreementCommencedOnOctoberTwentyFourTwoThousandAndEighteenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear" name="LesseeLeasingArrangementsOperatingLeasesExpiryMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_OperatingLeasesNumberOfLeasedFacilities" name="OperatingLeasesNumberOfLeasedFacilities" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_OperatingLeaseCommencementDate" name="OperatingLeaseCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_LeasePaymentsTerm" name="LeasePaymentsTerm" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_SubleasedFacilityNumberOfPortions" name="SubleasedFacilityNumberOfPortions" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_OperatingLeasesSubleaseCommencementDate" name="OperatingLeasesSubleaseCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable" name="OperatingLeasesSubleaseRevenuePlusReimbursementOfOperatingExpensesReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesSubleaseExpiryDate" name="OperatingLeasesSubleaseExpiryDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_OperatingLeasesLossOnSublease" name="OperatingLeasesLossOnSublease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesSubleaseRevenueReceivable" name="OperatingLeasesSubleaseRevenueReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearTwo" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearThree" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFour" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsYearFive" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseRentalsThereafter" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract" name="OperatingLeasesFutureMinimumPaymentsDueSubleaseIncomeAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_Partner1Member" name="Partner1Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_Partner2Member" name="Partner2Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_Partner3Member" name="Partner3Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NumberOfMajorPartners" name="NumberOfMajorPartners" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_RelatedPartyTransactionsPaymentsToRelatedParty" name="RelatedPartyTransactionsPaymentsToRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues" name="PercentageOfRelatedPartyPaymentOnRelatedPartyGrossRevenues" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_CooleyLLPMember" name="CooleyLLPMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_SubleaseAgreementMember" name="SubleaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_BioasisTechnologiesIncMember" name="BioasisTechnologiesIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing" name="NumberOfFutureCashPaymentsUponClosingOfQualifiedFinancing" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_FutureCashPaymentsUponClosingOfQualifiedFinancing" name="FutureCashPaymentsUponClosingOfQualifiedFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <element id="xoma_AdditionalCashReceiptsUponClosingOfQualifiedFinancing" name="AdditionalCashReceiptsUponClosingOfQualifiedFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <element id="xoma_PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing" name="PercentageOfNetProceedsOfEachFutureFinancingUponClosingOfTheQualifiedFinancing" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <element id="xoma_PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements" name="PercentageOfOptionalRoyaltyRightsPurchaseOnFutureLicenseAgreements" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <element id="xoma_QuarterlyFinancialInformationLineItems" name="QuarterlyFinancialInformationLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_QuarterlyFinancialInformationTable" name="QuarterlyFinancialInformationTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_JanssenBiotechIncorparationMember" name="JanssenBiotechIncorparationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <element id="xoma_LicenseAgreementAndCommonStockPurchaseAgreementMember" name="LicenseAgreementAndCommonStockPurchaseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</schema>
