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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Ey+Y0GoRZgNpKnBQtN409Zy/S4nRuBrpYgOZKB4oDAda3xj5ftzfPYJVaILOKBpC
 +oz0czTTVIuXRiie9P67Cg==

<SEC-DOCUMENT>0001225208-10-010435.txt : 20100416
<SEC-HEADER>0001225208-10-010435.hdr.sgml : 20100416
<ACCEPTANCE-DATETIME>20100416132537
ACCESSION NUMBER:		0001225208-10-010435
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100414
FILED AS OF DATE:		20100416
DATE AS OF CHANGE:		20100416

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GENZYME CORP
		CENTRAL INDEX KEY:			0000732485
		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
		IRS NUMBER:				061047163
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		500 KENDALL STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142
		BUSINESS PHONE:		6172527500

	MAIL ADDRESS:	
		STREET 1:		500 KENDALL STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			WHITWORTH RALPH V
		CENTRAL INDEX KEY:			0001052622

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-14680
		FILM NUMBER:		10754240

	MAIL ADDRESS:	
		STREET 1:		RELATIONAL INVESTORS LLC
		STREET 2:		12400 HIGH BLUFF DRIVE, SUITE 600
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92130
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc3.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-04-14</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000732485</issuerCik>
        <issuerName>GENZYME CORP</issuerName>
        <issuerTradingSymbol>GENZ</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001052622</rptOwnerCik>
            <rptOwnerName>WHITWORTH RALPH V</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>12400 HIGH BLUFF DR. #600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92130</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Genzyme common stock (GENZ)</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10622708</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>see footnote 1 and 2</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person is one of the Principals of Relational Investors LLC (&quot;RILLC&quot;). RILLC is the record owner of 100 shares and sole general partner, or the sole managing member of the general partner, of Relational Investors, L.P., Relational Fund Partners, L.P., Relational Coast Partners, L.P., RH Fund 1, L.P., RH Fund 6, L.P., Relational Investors III, L.P., Relational Investors VIII, L.P., Relational Investors IX, L.P., Relational Investors X, L.P., Relational Investors XV, L.P., Relational Investors XVI, L.P., Relational Investors XX, L.P., Relational Investors XXII, L.P., Relational Investors XXIII, L.P., and Relational Investors Alpha Fund I, L.P.</footnote>
        <footnote id="F2">The Limited Partnerships in footnote 1 own a total of 7,979,894 shares. An additional 2,234,214 shares are held in accounts managed by RILLC and an additional 408,500 shares are held through co-investment arrangements with certain entities listed in footnote 1. The reporting person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Susan P. Cogswell, Attorney-in-Fact</signatureName>
        <signatureDate>2010-04-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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