-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 DP7BBvKKN8NiCMiQOj0KM+SnZNTtSRoSi2Mao2FxqX9VlLe0qRfxt9GrG8U3wNPJ
 wdoYYuW0nTrRXeaVHbyZ3w==

<SEC-DOCUMENT>0000950103-04-000803.txt : 20040602
<SEC-HEADER>0000950103-04-000803.hdr.sgml : 20040602
<ACCEPTANCE-DATETIME>20040602164028
ACCESSION NUMBER:		0000950103-04-000803
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040602
FILED AS OF DATE:		20040602

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IMMUNOGEN INC
		CENTRAL INDEX KEY:			0000855654
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				042726691
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		128 SIDNEY ST
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		6179952506

	MAIL ADDRESS:	
		STREET 1:		128 SIDNEY ST
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SHIRE BIOCHEM INC
		CENTRAL INDEX KEY:			0000867202
		STANDARD INDUSTRIAL CLASSIFICATION:	IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES [2835]
		STATE OF INCORPORATION:			E6
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-17999
		FILM NUMBER:		04844896

	BUSINESS ADDRESS:	
		STREET 1:		275 ARMAND-FRAPPIER BLVD
		CITY:			LAVAL QUEBEC
		STATE:			E6
		ZIP:			H7V 4A7
		BUSINESS PHONE:		5146811744

	MAIL ADDRESS:	
		STREET 1:		275 ARMAND FRAPPIER BLVD
		CITY:			LAVAL QUEBEC
		STATE:			E6
		ZIP:			H7V 4A7

	FORMER NAME:	
		FORMER CONFORMED NAME:	BIOCHEM PHARMA INC
		DATE OF NAME CHANGE:	19930504

	FORMER NAME:	
		FORMER CONFORMED NAME:	IAF BIOCHEM INTERNATIONAL INC
		DATE OF NAME CHANGE:	19920310

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SHIRE PHARMACEUTICALS GROUP PLC
		CENTRAL INDEX KEY:			0000936402
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-17999
		FILM NUMBER:		04844897

	BUSINESS ADDRESS:	
		STREET 1:		HAMPSHIRE INTL BUSINESS PARK
		STREET 2:		CHINEHAM BASINGSTOKE
		CITY:			HAMPSHIRE ENGLAND RG
		STATE:			X0
		BUSINESS PHONE:		1264333455

	MAIL ADDRESS:	
		STREET 1:		HAMPSHIRE INTL BUSINESS PARK
		STREET 2:		CHINEHAM BASINGSTOKE
		CITY:			HAMPSHIRE ENGLAND RG
		STATE:			X0
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>jun0204_4shireex.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-06-02</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000855654</issuerCik>
        <issuerName>IMMUNOGEN INC</issuerName>
        <issuerTradingSymbol>IMGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000867202</rptOwnerCik>
            <rptOwnerName>SHIRE BIOCHEM INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>275 ARMAND-FRAPPIER BLVD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LAVAL QUEBEC</rptOwnerCity>
            <rptOwnerState>A8</rptOwnerState>
            <rptOwnerZipCode>H7V 4A7</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000936402</rptOwnerCik>
            <rptOwnerName>SHIRE PHARMACEUTICALS GROUP PLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>HAMPSHIRE INTL BUSINESS PARK</rptOwnerStreet1>
            <rptOwnerStreet2>CHINEHAM BASINGSTOKE</rptOwnerStreet2>
            <rptOwnerCity>HAMPSHIRE ENGLAND RG</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2004-06-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4030000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>6.7125</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>66098</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These shares were owned directly by Shire BioChem Inc., which is a wholly-owned subsidiary of Shire Pharmaceuticals Group plc. Shire Pharmaceuticals Group plc was an indirect beneficial owner of the reported securities.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Angus Russell, Director, Shire BioChem Inc.</signatureName>
        <signatureDate>2004-06-02</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Angus Russell, Director, Shire Pharmaceuticals Group plc</signatureName>
        <signatureDate>2004-06-02</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----