<SUBMISSION>
<ACCESSION-NUMBER>0001005477-05-000224
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20050119
<FILING-DATE>20050121
<DATE-OF-FILING-DATE-CHANGE>20050121
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>AEROGEN INC
<CIK>0001039160
<ASSIGNED-SIC>3841
<IRS-NUMBER>330488580
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>2071 STIERLIN COURT
<CITY>MOUNTAIN VIEW
<STATE>CA
<ZIP>94043
<PHONE>650 864-7300
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>2071 STIERLIN COURT
<CITY>MOUNTAIN VIEW
<STATE>CA
<ZIP>94043
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>XMARK ASSET MANAGEMENT LLC
<CIK>0001118481
<STATE-OF-INCORPORATION>NY
<FISCAL-YEAR-END>1231
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-31913
<FILM-NUMBER>05541800
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>CARNEGIE HALL TOWER
<STREET2>152 W 57TH ST 21ST FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
<PHONE>2122478200
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>CARNEGIE HALL TOWER
<STREET2>152 W 57TH ST 21ST FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
</MAIL-ADDRESS>
<FORMER-NAME>
<FORMER-CONFORMED-NAME>BROWN SIMPSON ASSET MANAGEMENT LLC
<DATE-CHANGED>20000707
</FORMER-NAME>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar123.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-01-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001039160</issuerCik>
        <issuerName>AEROGEN INC</issuerName>
        <issuerTradingSymbol>AEGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001118481</rptOwnerCik>
            <rptOwnerName>XMARK ASSET MANAGEMENT LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 TRESSER BOULEVARD, SUITE 1320</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrant</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.25</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-01-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>764610</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2009-03-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.001 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>764610</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrant</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.25</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-01-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>902050</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2009-05-11</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.001 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>902050</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Xmark Asset Management, LLC, a New York limited liability company (&quot;XAM&quot;), serves as investment manager for each of Xmark Fund, L.P., a Delaware limited partnership (&quot;Xmark LP&quot;), and Xmark Fund, Ltd., a Cayman Islands exempted company (&quot;Xmark Ltd&quot;).  In such capacity, XAM possesses the power to vote and direct the disposition of all securities held by Xmark LP and Xmark Ltd.  As of January 19, 2005, Xmark LP is the holder of (i) 74,025 shares (the &quot;Xmark LP Preferred&quot;) of the Series A-1 Preferred Stock, par value $0.001 per share (the &quot;Preferred Stock&quot;) of Aerogen, Inc., a Delaware corporation (the &quot;Company&quot;), which are presently convertible into 740,250 shares of the Company's common stock, par value $0.001 per share (the &quot;Common Stock&quot;) and (ii) 23,560 shares of Common Stock issued in lieu of the cash payment of quarterly dividends on the Preferred Stock held by Xmark LP for the quarters ended March 31, June 30 and September 30, 2004.  Holders of Preferred Stock</footnote>
        <footnote id="F2">are entitled to receive dividends quarterly in arrears, in cash or Common Stock, at the Company's election, as more fully described in the Certificate of Designations, Preferences and Rights of the Company's Preferred Stock.  As of January 19, 2005, Xmark Ltd is the holder of (i) 92,641 shares (the &quot;Xmark Ltd Preferred&quot;) of Preferred Stock, which are presently convertible into 926,410 shares of Common Stock and (ii) 29,483 shares of Common Stock issued in lieu of the cash payment of quarterly dividends on the Preferred Stock held by Xmark Ltd for the quarters ended March 31, June 30 and September 30, 2004.  The terms of the Xmark LP Preferred and  the Xmark Ltd Preferred originally precluded each of Xmark LP and Xmark Ltd from converting the Xmark LP Preferred and the Xmark Ltd Preferred if the conversion would result in Xmark LP, Xmark Ltd and/or their affiliates beneficially owning in excess of 4.99% of the Company's outstanding Common Stock following the conversion</footnote>
        <footnote id="F3">(the &quot;Issuance Limitation&quot;).  Each such Issuance Limitation was waiveable by Xmark LP and Xmark Ltd, respectively, providing 61 days' advance written notice to the Company.  On November 3, 2004, Xmark Fund, LP and Xmark Fund, Ltd each provided a written waiver of the Issuance Limitation to the Company.  As a result of this waiver and as a result of the fact that XAM possesses the sole power to vote and direct the disposition of the securities described above, for purposes of Reg. Section 240.13d-3, XAM may be deemed to beneficially own 1,719,703 shares of Common Stock, or approximately 26.3% of the shares of Common Stock deemed issued and outstanding as of January 19, 2005.  XAM's interest in the securities reported herein is limited to its pecuniary interest in Xmark LP and Xmark Ltd, if any.  Mitchell D. Kaye is Chief Investment Officer of XAM, and as such possesses sole power to vote and direct the disposition of all securities of the Company held by Xmark LP and Xmark Ltd.</footnote>
        <footnote id="F4">The warrants were immediately exercisable.</footnote>
        <footnote id="F5">On January 19, 2005, Xmark LP and Xmark Ltd sold a total of 1,666,660 warrants for an aggregate purchase price of $383,331.80.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Mitchell D. Kaye, Manager of Xmark Asset Management, LLC</signatureName>
        <signatureDate>2005-01-21</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
