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

    <documentType>4</documentType>
	<periodOfReport>2003-06-30</periodOfReport>
	<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000732485</issuerCik>
        <issuerName>GENZYME CORP</issuerName>
        <issuerTradingSymbol>GENZ</issuerTradingSymbol>
	</issuer>
	<reportingOwner>
		<reportingOwnerId>
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            <rptOwnerName>CSIMMA ZOLTAN A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
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			<isOfficer>1</isOfficer>
			<isTenPercentOwner>0</isTenPercentOwner>
			<isOther>0</isOther>
			<officerTitle>Senior VP, Human Resources</officerTitle>
		</reportingOwnerRelationship>
	</reportingOwner>
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		<securityTitle>
			<value>Genzyme General common stock (GENZ)</value>
		</securityTitle>
		<transactionDate>
			<value>2003-06-30</value>
		</transactionDate>
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			<transactionValue>
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		<ownershipNature>
			<directOrIndirectOwnership>
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			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
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	<nonDerivativeSecurity>
		<securityTitle>
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		</securityTitle>
		<transactionDate>
			<value>2003-06-30</value>
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			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</nonDerivativeSecurity>
	<derivativeSecurity>
		<securityTitle>
			<value>Biosurgery NQ stock option (right to buy)</value>
		</securityTitle>
		<conversionOrExercisePrice>
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		<transactionDate>
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			<footnoteId id="F3"/>
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		<expirationDate>
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			<underlyingSecurityTitle>
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			<natureOfOwnership>
				<value/>
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	<derivativeSecurity>
		<securityTitle>
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		</underlyingSecurity>
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		<securityTitle>
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				<value>0</value>
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			<transactionAcquiredDisposedCode>
				<value>D</value>
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			<value>2003-07-17</value>
			<footnoteId id="F5"/>
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		<expirationDate>
			<value>2010-07-17</value>
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		<underlyingSecurity>
			<underlyingSecurityTitle>
				<value>Genzyme Molecular Oncology common stock (GZMO)</value>
			</underlyingSecurityTitle>
			<underlyingSecurityShares>
				<value>11302</value>
			</underlyingSecurityShares>
		</underlyingSecurity>
		<postTransactionAmounts>
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				<value>0</value>
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				<value>D</value>
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			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</derivativeSecurity>
	<derivativeSecurity>
		<securityTitle>
			<value>Molecular Oncology NQ stock option (right to buy)</value>
		</securityTitle>
		<conversionOrExercisePrice>
			<value>15.40</value>
		</conversionOrExercisePrice>
		<transactionDate>
			<value>2003-06-30</value>
		</transactionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>J</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>8000</value>
				<footnoteId id="F2"/>
			</transactionShares>
			<transactionValue>
				<value>0</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>D</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<exerciseDate>
			<value>2001-05-31</value>
			<footnoteId id="F4"/>
		</exerciseDate>
		<expirationDate>
			<value>2011-05-31</value>
		</expirationDate>
		<underlyingSecurity>
			<underlyingSecurityTitle>
				<value>Genzyme Molecular Oncology common stock (GZMO)</value>
			</underlyingSecurityTitle>
			<underlyingSecurityShares>
				<value>8000</value>
			</underlyingSecurityShares>
		</underlyingSecurity>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>0</value>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</derivativeSecurity>
	<derivativeSecurity>
		<securityTitle>
			<value>Molecular Oncology NQ stock option (right to buy)</value>
		</securityTitle>
		<conversionOrExercisePrice>
			<value>2.33</value>
		</conversionOrExercisePrice>
		<transactionDate>
			<value>2003-06-30</value>
		</transactionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>J</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>10300</value>
				<footnoteId id="F2"/>
			</transactionShares>
			<transactionValue>
				<value>0</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>D</value>
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		<exerciseDate>
			<value>2002-05-30</value>
			<footnoteId id="F4"/>
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		<expirationDate>
			<value>2012-05-30</value>
		</expirationDate>
		<underlyingSecurity>
			<underlyingSecurityTitle>
				<value>Genzyme Molecular Oncology common stock (GZMO)</value>
			</underlyingSecurityTitle>
			<underlyingSecurityShares>
				<value>10300</value>
			</underlyingSecurityShares>
		</underlyingSecurity>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>0</value>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</derivativeSecurity>
	<footnotes>
		<footnote id="F1">On June 30, 2003 all outstanding shares of Genzyme Biosurgery and Genzyme Molecular stock were exchanged for shares of Genzyme General Stock.  Genzyme Biosurgery shareholders received .04914 of a share of Genzyme General stock for each Biosurgery share and Genzyme Molecular Oncology shareholders received .05653 of a share of Genzyme General stock for each Molecular Oncology share.</footnote>
		<footnote id="F2">On June 30, 2003 in relation to the elimination of Genzyme's tracking stock structure, all stock options of Genzyme Biosurgery and Genzyme Molecular were exchanged for stock options of Genzyme General.  The exchange ratio was based on the closing prices of all three stocks on 6/30/03.  Genzyme Biosurgery options were exchanged at a rate of .04945 and Genzyme Molecular Oncology options were exchanged at a rate of .05614.</footnote>
		<footnote id="F3">Options vest in 25% annual increments on July 17, 2001, 2002, 2003 and 2004.</footnote>
		<footnote id="F4">Options vest in 20% annual increments beginning on the original date of grant.</footnote>
		<footnote id="F5">Options were granted with an exercise price 20% above fair market value, and vest in 1/3 increments on each of July 17, 2003, 2004 and 2005.</footnote>
	</footnotes>
	<ownerSignature>
		<signatureName>By: Susan P. Cogswell, Attorney-in-Fact</signatureName>
		<signatureDate>2003-07-01</signatureDate>
	</ownerSignature>
</ownershipDocument>
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X0101
4
2003-06-30
0
0000732485
GENZYME CORP
GENZ
0001201255
CSIMMA ZOLTAN A
0
1
0
0
Senior VP, Human Resources
Genzyme General common stock (GENZ)
2003-06-30
4
J
0
12
0
A
982
D
Genzyme Molecular Oncology common stock (GZMO)
2003-06-30
4
J
0
225
0
D
0
D
Biosurgery NQ stock option (right to buy)
6.69
2003-06-30
4
J
0
10000
0
D
2001-07-17
2011-02-09
Genzyme Biosurgery common stock (GZBX)
10000
0
D
Biosurgery NQ stock option (right to buy)
6.26
2003-06-30
4
J
0
8000
0
D
2001-05-31
2011-05-31
Genzyme Biosurgery common stock (GZBX)
8000
0
D
Biosurgery NQ stock option (right to buy)
4.24
2003-06-30
4
J
0
13000
0
D
2002-05-30
2012-05-30
Genzyme Biosurgery common stock (GZBX)
13000
0
D
Genzyme General NQ stock option (righ to buy)
126.60
2003-06-30
4
J
0
395
0
A
2001-05-31
2011-05-31
Genzyme General common stock (GENZ)
395
395
D
Genzyme General NQ stock option (right to buy)
292.67
2003-06-30
4
J
0
634
0
A
2003-07-17
2010-07-17
Genzyme General common stock (GENZ)
634
634
D
Genzyme General NQ stock option (right to buy)
135.29
2003-06-30
4
J
0
494
0
A
2001-07-17
2011-02-09
Genzyme General common stock (GENZ)
494
494
D
Genzyme General NQ stock option (right to buy)
274.32
2003-06-30
4
J
0
449
0
A
2001-05-31
2011-05-31
Genzyme General common stock (GENZ)
449
449
D
Genzyme General NQ stock option (right to buy)
85.75
2003-06-30
4
J
0
642
0
A
2002-05-30
2012-05-30
Genzyme General common stock (GENZ)
642
642
D
Genzyme General NQ stock option (right to buy)
41.51
2003-06-30
4
J
0
578
0
A
2002-05-30
2012-05-30
Genzyme General common stock (GENZ)
578
578
D
Genzyme General NQ stockoption (right to buy)
243.86
2003-06-30
4
J
0
561
0
A
2001-07-17
2010-07-17
Genzyme General common stock (GENZ)
561
561
D
Molecular Oncology NQ stock option (right to buy)
13.69
2003-06-30
4
J
0
10000
0
D
2001-07-17
2010-07-17
Genzyme Molecular Oncology common stock (GZMO)
10000
0
D
Molecular Oncology NQ stock option (right to buy)
16.43
2003-06-30
4
J
0
11302
0
D
2003-07-17
2010-07-17
Genzyme Molecular Oncology common stock (GZMO)
11302
0
D
Molecular Oncology NQ stock option (right to buy)
15.40
2003-06-30
4
J
0
8000
0
D
2001-05-31
2011-05-31
Genzyme Molecular Oncology common stock (GZMO)
8000
0
D
Molecular Oncology NQ stock option (right to buy)
2.33
2003-06-30
4
J
0
10300
0
D
2002-05-30
2012-05-30
Genzyme Molecular Oncology common stock (GZMO)
10300
0
D
On June 30, 2003 all outstanding shares of Genzyme Biosurgery and Genzyme Molecular stock were exchanged for shares of Genzyme General Stock.  Genzyme Biosurgery shareholders received .04914 of a share of Genzyme General stock for each Biosurgery share and Genzyme Molecular Oncology shareholders received .05653 of a share of Genzyme General stock for each Molecular Oncology share.
On June 30, 2003 in relation to the elimination of Genzyme's tracking stock structure, all stock options of Genzyme Biosurgery and Genzyme Molecular were exchanged for stock options of Genzyme General.  The exchange ratio was based on the closing prices of all three stocks on 6/30/03.  Genzyme Biosurgery options were exchanged at a rate of .04945 and Genzyme Molecular Oncology options were exchanged at a rate of .05614.
Options vest in 25% annual increments on July 17, 2001, 2002, 2003 and 2004.
Options vest in 20% annual increments beginning on the original date of grant.
Options were granted with an exercise price 20% above fair market value, and vest in 1/3 increments on each of July 17, 2003, 2004 and 2005.
By: Susan P. Cogswell, Attorney-in-Fact
2003-07-01