Agreement

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                                                            Exhibit 10.16

          Confidential Materials omitted and filed separately with the

         Securities and Exchange Commission. Asterisks denote omissions.

February 1, 2005

Dennis P. Bauer, Ph.D.

Siegfried (USA), Inc.

33 Industrial Park Road

Pennsville, NJ 08070

Dear Dennis:

Reference is made to the Development and Production Agreement for Active

Pharmaceutical Ingredient between Siegfried (USA), Inc. and Siegfried Ltd.

("SIEGFRIED") and Momenta Pharmaceuticals, Inc. ("MOMENTA") dated October 10,

2003, as amended or supplemented by Letter Agreement dated February 14, 2004,

May 17, 2004, September 29, 2004 and January 26, 2005 (the "Agreement").

Capitalized terms used herein and not otherwise defined shall have the meanings

given such terms in the Agreement.

Pursuant to the Letter Agreement dated September 29, 2004,