- Statement of Changes in Beneficial Ownership (4)

FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES	OMB APPROVAL OMB Number: 3235-0287 Expires: February 28, 2011 Estimated average burden hours per response... 0.5
	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(f) of the Investment Company Act of 1940

1. Name and Address of Reporting Person ^* BERTHIAUME DOUGLAS A	2. Issuer Name and Ticker or Trading Symbol GENZYME CORP [ GENZ ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __ X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below)
(Last) (First) (Middle) 500 KENDALL STREET	3. Date of Earliest Transaction (MM/DD/YYYY) 4/4/2011
(Street) CAMBRIDGE, MA 02142 (City) (State) (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) _ X _ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Genzyme common stock (GENZ)	4/4/2011		M		2375.0000	A	$0.0000	73533.0000	D
Genzyme common stock (GENZ)	4/4/2011		M		949.9060	A	$0 ⁽¹⁾	74482.9060	D
Genzyme common stock (GENZ)	4/4/2011		M		609.9520	A	$0 ⁽¹⁾	75092.8580	D
Genzyme common stock (GENZ)	4/4/2011		M		511.4740	A	$0 ⁽¹⁾	75604.3320	D
Genzyme common stock (GENZ)	4/4/2011		M		445.1490	A	$0 ⁽¹⁾	76049.4810	D
Genzyme common stock (GENZ)	4/4/2011		M		430.3220	A	$0 ⁽¹⁾	76479.8030	D
Genzyme common stock (GENZ)	4/4/2011		M		419.9370	A	$0 ⁽¹⁾	76899.7400	D
Genzyme common stock (GENZ)	4/4/2011		M		406.7110	A	$0 ⁽¹⁾	77306.4510	D
Genzyme common stock (GENZ)	4/4/2011		M		405.7100	A	$0 ⁽¹⁾	77712.1610	D
Genzyme common stock (GENZ)	4/4/2011		M		391.9930	A	$0 ⁽¹⁾	78104.1540	D
Genzyme common stock (GENZ)	4/4/2011		M		368.9370	A	$0 ⁽¹⁾	78473.0910	D
Genzyme common stock (GENZ)	4/4/2011		M		322.9000	A	$0 ⁽¹⁾	78795.9910	D
Genzyme common stock (GENZ)	4/4/2011		M		318.3280	A	$0 ⁽¹⁾	79114.3190	D
Genzyme common stock (GENZ)	4/4/2011		M		314.6960	A	$0 ⁽¹⁾	79429.0150	D
Genzyme common stock (GENZ)	4/4/2011		M		292.7520	A	$0 ⁽¹⁾	79721.7670	D
Genzyme common stock (GENZ)	4/4/2011		M		286.4980	A	$0 ⁽¹⁾	80008.2650	D
Genzyme common stock (GENZ)	4/4/2011		M		274.7090	A	$0 ⁽¹⁾	80282.9740	D
Genzyme common stock (GENZ)	4/4/2011		M		266.9520	A	$0 ⁽¹⁾	80549.9260	D
Genzyme common stock (GENZ)	4/4/2011		M		262.3920	A	$0 ⁽¹⁾	80812.3180	D
Genzyme common stock (GENZ)	4/4/2011		M		254.7720	A	$0 ⁽¹⁾	81067.0900	D
Genzyme common stock (GENZ)	4/4/2011		M		233.4010	A	$0 ⁽¹⁾	81300.4910	D
Genzyme common stock (GENZ)	4/4/2011		M		230.1370	A	$0 ⁽¹⁾	81530.6280	D
Genzyme common stock (GENZ)	4/4/2011		M		224.0250	A	$0 ⁽¹⁾	81754.6530	D
Genzyme common stock (GENZ)	4/4/2011		M		211.1210	A	$0 ⁽¹⁾	81965.7740	D
Genzyme common stock (GENZ)	4/4/2011		M		208.5310	A	$0 ⁽¹⁾	82174.3050	D
Genzyme common stock (GENZ)	4/4/2011		M		188.5800	A	$0 ⁽¹⁾	82362.8850	D
Genzyme common stock (GENZ)	4/4/2011		M		175.9750	A	$0 ⁽¹⁾	82538.8600	D
Genzyme common stock (GENZ)	4/4/2011		D		2375.0000	D	$74.0000	80163.8600	D
Genzyme common stock (GENZ)	4/4/2011		D		9005.8600	D	$76.0100	71158.0000	D
Genzyme common stock (GENZ)	4/4/2011		U		71158.0000	D	$74.0000	0.0000	D

*Table II - Derivative Securities Beneficially Owned ( e.g.* , puts, calls, warrants, options, convertible securities)**
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)			11. Nature of Indirect Beneficial Ownership (Instr. 4)
Phantom Stock	⁽¹⁾	4/4/2011		M			254.7720	3/31/2005 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	254.7720	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			211.1210	3/31/2006 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	211.1210	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			286.4980	3/31/2007 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	286.4980	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			314.6960	3/31/2008 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	314.6960	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			405.7100	3/31/2009 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	405.7100	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			511.4740	3/31/2010 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	511.4740	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			274.7090	6/30/2004 ⁽¹⁾	12/20/2034	Genzyme common stock (GENZ)	274.7090	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			208.5310	6/30/2005 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	208.5310	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			266.9520	6/30/2006 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	266.9520	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			230.1370	6/30/2007 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	230.1370	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			368.9370	6/30/2008 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	368.9370	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			430.3220	6/30/2009 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	430.3220	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			949.9060	6/30/2010 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	949.9060	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			188.5800	9/30/2004 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	188.5800	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			175.9750	9/30/2005 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	175.9750	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			224.0250	9/30/2006 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	224.0250	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			318.3280	9/30/2007 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	318.3280	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			262.3920	9/30/2008 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	262.3920	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			406.7110	9/30/2009 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	406.7110	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			233.4010	12/31/2004 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	233.4010	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			292.7520	12/31/2005 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	292.7520	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			445.1490	12/31/2006 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	445.1490	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			391.9930	12/31/2007 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	391.9930	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			419.9370	12/31/2008 ⁽¹⁾	12/31/2034	Genzyme common stock (GENZ)	419.9370	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			609.9520	12/31/2009 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	609.9520	$0.0000	0.0000	D
Phantom Stock	⁽¹⁾	4/4/2011		M			322.9000	12/31/2010 ⁽¹⁾	⁽¹⁾	Genzyme common stock (GENZ)	322.9000	$0.0000	0.0000	D
Restricted Stock Units	$0.0000	4/4/2011		M			2375.0000	⁽²⁾	⁽²⁾	Genzyme common stock (GENZ)	2375.0000	$0.0000	0.0000	D
Stock Option (right to buy)	$51.5200	4/4/2011		D			7125.0000	⁽³⁾	6/16/2020	Genzyme common stock (GENZ)	7125.0000	$51.5200	0.0000	D
Stock Option (right to buy)	$43.9000	4/4/2011		D			15000.0000	5/27/2005 ⁽³⁾	5/27/2014	Genzyme common stock (GENZ)	15000.0000	$43.9000	0.0000	D
Stock Option (right to buy)	$53.4700	4/4/2011		D			18000.0000	5/31/2002 ⁽³⁾	5/31/2011	Genzyme common stock (GENZ)	18000.0000	$53.4700	0.0000	D

Explanation of Responses:
( 1)	The phantom stock acquired under the Genzyme Directors? Deferred Compensation Plan was cancelled at the completion of the sanofi-aventis tender offer and converted into the right to receive a cash payment based on the closing price of Genzyme common stock on the last day it traded. Phantom stock was credited to the Reporting Person?s stock account under the deferred compensation at the end of each fiscal quarter from Apiril 1, 2004 through December 31, 2010, pursuant to the Reporting Person?s plan election and the terms of the plan.
( 2)	The vested restricted stock units were scheduled to vest on the date of the 2011 annual meeting of shareholders.
( 3)	This option, which provided for vesting at the next annual meeting of shareholders, was cancelled upon the consummation of the sanofi-aventis tender offer in exchange for a payment representing (A) an amount of cash equal to the excess of $74.00 over the exercise price of the option, multiplied by the total number of shares subject to such options, and (B) one contingent value right (CVR) per cancelled option.

Remarks:
,Multiple Forms Submitted

Reporting Owners
Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
BERTHIAUME DOUGLAS A 500 KENDALL STREET CAMBRIDGE, MA 02142	X

Signatures
Susan P. Cogswell, Attorney-in-Fact		4/6/2011
^** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
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