[Palmer & Dodge LLP]

                                                                     Exhibit 5.2
Telephone: (617) 573-0100                              FACSIMILE: (617) 227-4420



                                  July 14, 2000

Genzyme Corporation
One Kendall Square
Cambridge, MA  02139

         Reference is made to our opinion dated March 3, 2000 and included as
Exhibit 5.1 to the Registration Statement on Form S-3 (the "Registration
Statement") filed on March 3, 2000 by Genzyme Corporation (the "Company"), a
Massachusetts corporation, with the Securities and Exchange Commission (the
"Commission") under the Securities Act of 1933, as amended (the "Securities
Act"). We are rendering this supplemental opinion in connection with the
prospectus supplement (the "Prospectus Supplement") and base prospectus (the
"Base Prospectus") filed on or about July 14, 2000 by the Company with the
Commission pursuant to Rule 424 under the Securities Act. The Prospectus
Supplement relates to the offering by the Company of up to 1,464,700 shares of
Genzyme Molecular Oncology Division Common Stock, $0.01 par value per share (the
"Shares"), which Shares are covered by the Registration Statement. We understand
that the Shares are to be offered and sold in the manner described in the
Prospectus Supplement.

         We have acted as your counsel in connection with the preparation of the
Registration Statement, the Prospectus Supplement and the Base Prospectus. We
are familiar with the proceedings of the Board of Directors of the Company in
connection with the authorization, issuance and sale of the Shares. We have
examined such other documents as we consider necessary to render this opinion.

         Based upon the foregoing, we are of the opinion that the Shares have
been duly authorized and, when issued and delivered by the Company against
payment therefore as contemplated by the Prospectus Supplement, will be validly
issued, fully paid and non-assessable.

         We hereby consent to the filing of this opinion as a part of the
Registration Statement and to the reference of our firm under the caption "Legal
Matters" in the Base Prospectus.

                                                     Very truly yours,

                                                     /s/ Palmer & Dodge LLP

                                                     Palmer & Dodge LLP