**EXHIBIT 2.4**

**AMENDMENTNO. 1 TO AGREEMENT AND PLAN OF MERGER**

This Amendment No.1 to Agreement and Plan of Merger (this “Amendment”) is made as ofAugust 8, 2007, by and among Genzyme Corporation, a Massachusetts corporation (“Parent”),Wichita Bio Corporation, a Delaware corporation and a wholly owned subsidiaryof Genzyme (“Sub”), and Bioenvision, Inc., a Delaware corporation (the “Company”).

WHEREAS, theparties have entered into that certain Agreement and Plan of Merger dated as ofMay 29, 2007 (the “Merger Agreement”), which provides that Sub be mergedwith and into the Company on the terms and subject to the conditions set forthin the Merger Agreement; and

WHEREAS, theparties wish to amend the terms of the Merger Agreement;

NOW, THEREFORE,for good and valuable consideration, the receipt and sufficiency of which arehereby acknowledged, the parties agree as follows:

1.             In the first sentence of Section2.4 of the Merger Agreement, the phrase “Acceptance Date” is hereby deleted inits entirety and replaced with the phrase “Effective Time.”

2.             In the second sentence of Section5.3 of the Merger Agreement, the phrase “scheduled expiration date” is herebydeleted in its entirety and replaced with the phrase “date scheduled for theSpecial Meeting.”

3.             Genzyme, Sub, and the Company eachrepresents and warrants that it has full corporate power and authority to enterinto this Amendment and that all corporate action on its part necessary toauthorize this Amendment (other than the approval of the Merger (as defined inthe Merger Agreement)), as contemplated by Section 8.4 of the Merger Agreement,has been taken.

4.             Except as expressly modifiedhereby, the Merger Agreement shall remain in full force and effect inaccordance with its original terms.

5.             This Amendment and all actionsarising under or in connection therewith shall be governed by and construed inaccordance with the laws of the State of Delaware, regardless of the laws thatmight otherwise govern under applicable principles of conflicts of law thereof,*provided, however,* that the laws of therespective jurisdictions of incorporation of each of the parties shall governthe relative rights, obligations, powers, duties and other internal affairs ofsuch party and its board of directors.

6.             This Amendment may be executed intwo or more counterparts, each of which shall be deemed an original, and all ofwhich together shall constitute one and the same instrument.

7.             The parties hereto acknowledge andagree that certain of the provisions of this Amendment address scrivener’serrors in the Merger Agreement.

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IN WITNESSWHEREOF, the parties have executed this Amendment No. 2 to Agreement and Planof Merger as of the date first stated above.
|   | GENZYME CORPORATION      |
|--------|--------------------------|
|   |                     |   |
|   |                     |   |
|   | By:                      |  /s/ Earl  M. Collier, Jr. |   |
|   |                     |   Earl M. Collier, Jr. |
|   |                     |   Executive Vice President |
|   |                     |   |
|   |                     |   |
|   | WICHITA BIO  CORPORATION |
|   |                     |   |
|   |                     |   |
|   | By:                      |  /s/ Earl  M. Collier, Jr. |   |
|   |                     |   Earl M. Collier, Jr. |
|   |                     |   President |
|   |                     |   |
|   |                     |   |
|   | BIOENVISION,  INC.       |
|   |                     |   |
|   |                     |   |
|   | By:                      | /s/ Christopher  B. Wood |   |
|   |                     |   Christopher B. Wood |
|   |                     |   Chairman & Chief Executive Officer |
|        |                          |  |  |  |  |

 

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