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
                                                                                  
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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 *

MOSCICKI RICHARD A 		2. Issuer Name and Ticker or Trading Symbol

GENZYME CORP [ GENZ ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                      _____ 10% Owner
__ X __ Officer (give title below)      _____ Other (specify below)
Sr VP,Chief Medical Officer
(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)
Code V Amount (A) or (D) Price
Genzyme common stock (GENZ)   4/4/2011     M    8083.0000   A $0   (1) 28913.0000   D    
Genzyme common stock (GENZ)   4/4/2011     M    7679.0000   A $0   (1) 36592.0000   D    
Genzyme common stock (GENZ)   4/4/2011     D    15762.0000   D $74.0000   20830.0000   D    
Genzyme common stock (GENZ)   4/4/2011     U    20830.0000   D $74.0000   0.0000   D    
Genzyme common stock (GENZ)   4/4/2011     U    218.0000   D $74.0000   0.0000   I   By 401(k)  

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)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Restricted Stock Units     (1) 4/4/2011     M         7679.0000    5/21/2012   (1)   (1) Genzyme common stock (GENZ)   7679.0000   $0.0000   0.0000   D    
Restricted Stock Units     (1) 4/4/2011     M         8083.0000    5/22/2011   (1)   (1) Genzyme common stock (GENZ)   8083.0000   $0.0000   0.0000   D    
Stock Option (right to buy)   $51.5200   4/4/2011     D         23038.0000      (2) 6/16/2020   Genzyme common stock (GENZ)   23038.0000   $51.5200   0.0000   D    
Stock Option (right to buy)   $58.6600   4/4/2011     D         23038.0000    5/21/2009   (2) 5/21/2019   Genzyme common stock (GENZ)   23038.0000   $58.6600   0.0000   D    
Stock Option (right to buy)   $68.4800   4/4/2011     D         24250.0000    5/22/2008   (2) 5/22/2018   Genzyme common stock (GENZ)   24250.0000   $68.4800   0.0000   D    
Stock Option (right to buy)   $62.1600   4/4/2011     D         24250.0000    5/24/2007   (2) 5/24/2017   Genzyme common stock (GENZ)   24250.0000   $62.1600   0.0000   D    
Stock Option (right to buy)   $58.5000   4/4/2011     D         48500.0000    5/25/2006   (2) 5/25/2016   Genzyme common stock (GENZ)   48500.0000   $58.5000   0.0000   D    
Stock Option (right to buy)   $62.9800   4/4/2011     D         48500.0000    5/26/2005   (2) 5/26/2015   Genzyme common stock (GENZ)   48500.0000   $62.9800   0.0000   D    
Stock Option (right to buy)   $43.9000   4/4/2011     D         57000.0000    5/27/2004   (2) 5/27/2014   Genzyme common stock (GENZ)   57000.0000   $43.9000   0.0000   D    
Stock Option (right to buy)   $46.2400   4/4/2011     D         45000.0000    5/29/2003   (2) 5/29/2013   Genzyme common stock (GENZ)   45000.0000   $46.2400   0.0000   D    
Stock Option (right to buy)   $41.5000   4/4/2011     D         830.0000    5/30/2002   (2) 5/30/2012   Genzyme common stock (GENZ)   830.0000   $41.5000   0.0000   D    
Stock Option (right to buy)   $32.5200   4/4/2011     D         80311.0000    5/30/2002   (2) 5/30/2012   Genzyme common stock (GENZ)   80311.0000   $32.5200   0.0000   D    
Stock Option (right to buy)   $32.5200   4/4/2011     D         13289.0000    5/30/2005   (2) 5/30/2012   Genzyme common stock (GENZ)   13289.0000   $32.5200   0.0000   D    
Stock Option (right to buy)   $53.4700   4/4/2011     D         41000.0000    5/31/2001   (2) 5/31/2011   Genzyme common stock (GENZ)   41000.0000   $53.4700   0.0000   D    
Stock Option (right to buy)   $43.3000   4/4/2011     D         10000.0000    7/10/2003   (2) 7/10/2013   Genzyme common stock (GENZ)   10000.0000   $43.3000   0.0000   D    

Explanation of Responses:
( 1)  The vested restricted stock units were scheduled to be released on 5/22/2011 and 5/21/2012.
( 2)  This option, which provided for vesting 20% at grant and 20% annually over four years, 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.

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

Sr VP,Chief Medical Officer

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).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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