<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
	<periodOfReport>2003-07-09</periodOfReport>
	<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000732485</issuerCik>
        <issuerName>GENZYME CORP</issuerName>
        <issuerTradingSymbol>GENZ</issuerTradingSymbol>
	</issuer>
	<reportingOwner>
		<reportingOwnerId>
            <rptOwnerCik>0001021037</rptOwnerCik>
            <rptOwnerName>SMITH ALAN E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
			<isDirector>0</isDirector>
			<isOfficer>1</isOfficer>
			<isTenPercentOwner>0</isTenPercentOwner>
			<isOther>0</isOther>
			<officerTitle>Senior Vice President</officerTitle>
		</reportingOwnerRelationship>
	</reportingOwner>
	<nonDerivativeSecurity>
		<securityTitle>
			<value>Genzyme General common stock (GENZ)</value>
		</securityTitle>
		<transactionDate>
			<value>2003-07-09</value>
		</transactionDate>
		<deemedExecutionDate>
			<value>2003-07-09</value>
		</deemedExecutionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>M</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>15000</value>
			</transactionShares>
			<transactionValue>
				<value>7.27</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>A</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>73986</value>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</nonDerivativeSecurity>
	<nonDerivativeSecurity>
		<securityTitle>
			<value>Genzyme General common stock (GENZ)</value>
		</securityTitle>
		<transactionDate>
			<value>2003-07-09</value>
		</transactionDate>
		<deemedExecutionDate>
			<value>2003-07-09</value>
		</deemedExecutionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>S</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
			<footnoteId id="F1"/>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>15000</value>
			</transactionShares>
			<transactionValue>
				<value>44.49</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>D</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>58986</value>
				<footnoteId id="F2"/>
				<footnoteId id="F3"/>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</nonDerivativeSecurity>
	<derivativeSecurity>
		<securityTitle>
			<value>Genzyme General NQ stock option (right to buy)</value>
		</securityTitle>
		<conversionOrExercisePrice>
			<value>7.27</value>
		</conversionOrExercisePrice>
		<transactionDate>
			<value>2003-07-09</value>
		</transactionDate>
		<deemedExecutionDate>
			<value>2003-07-09</value>
		</deemedExecutionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>M</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>15000</value>
			</transactionShares>
			<transactionValue>
				<value>0</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>D</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<exerciseDate>
			<value>2003-06-30</value>
		</exerciseDate>
		<expirationDate>
			<value>2003-12-08</value>
		</expirationDate>
		<underlyingSecurity>
			<underlyingSecurityTitle>
				<value>Genzyme General common stock (GENZ)</value>
			</underlyingSecurityTitle>
			<underlyingSecurityShares>
				<value>15000</value>
			</underlyingSecurityShares>
		</underlyingSecurity>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>75000</value>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</derivativeSecurity>
	<footnotes>
		<footnote id="F1">The sales reported were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on May 28, 2003.</footnote>
		<footnote id="F2">The exercise of this stock option included a distribution of an additional 3 shares of Genzyme common stock.  These stock options were entitled to receive a distribution of shares of Tissue Repair common stock that was paid on July 22, 1997 to Genzyme General Division stockholders at a rate of 0.015.  In connection with the formation of Genzyme Biosurgery in December 2000, shares of Genzyme Tissue Repair were converted into shares of Genzyme Biosurgery at a rate of 0.3352.  In connection with the exchange of Genzyme Biosurgery stock into Genzyme General stock on June 30, 2003, distributions of the Genzyme Biosurgery stock are exchanged into Genzyme General stock at a rate of 0.04945.</footnote>
		<footnote id="F3">Includes 518 shares purchased from the issuer's Employee Stock Purchase Plan on July 9, 2003.</footnote>
	</footnotes>
	<ownerSignature>
		<signatureName>By: Susan P. Cogswell, Attorney-in-Fact</signatureName>
		<signatureDate>2003-07-10</signatureDate>
	</ownerSignature>
</ownershipDocument>
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X0101
4
2003-07-09
0
0000732485
GENZYME CORP
GENZ
0001021037
SMITH ALAN E
0
1
0
0
Senior Vice President
Genzyme General common stock (GENZ)
2003-07-09
2003-07-09
4
M
0
15000
7.27
A
73986
D
Genzyme General common stock (GENZ)
2003-07-09
2003-07-09
4
S
0
15000
44.49
D
58986
D
Genzyme General NQ stock option (right to buy)
7.27
2003-07-09
2003-07-09
4
M
0
15000
0
D
2003-06-30
2003-12-08
Genzyme General common stock (GENZ)
15000
75000
D
The sales reported were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on May 28, 2003.
The exercise of this stock option included a distribution of an additional 3 shares of Genzyme common stock.  These stock options were entitled to receive a distribution of shares of Tissue Repair common stock that was paid on July 22, 1997 to Genzyme General Division stockholders at a rate of 0.015.  In connection with the formation of Genzyme Biosurgery in December 2000, shares of Genzyme Tissue Repair were converted into shares of Genzyme Biosurgery at a rate of 0.3352.  In connection with the exchange of Genzyme Biosurgery stock into Genzyme General stock on June 30, 2003, distributions of the Genzyme Biosurgery stock are exchanged into Genzyme General stock at a rate of 0.04945.
Includes 518 shares purchased from the issuer's Employee Stock Purchase Plan on July 9, 2003.
By: Susan P. Cogswell, Attorney-in-Fact
2003-07-10