Filed Pursuant to Rule 424(b)(2)
                                                      Registration No. 333-31548

PROSPECTUS SUPPLEMENT
TO PROSPECTUS DATED JULY 14, 2000

                                1,607,400 SHARES

                                    GENZYME

                          MOLECULAR ONCOLOGY DIVISION

                                  COMMON STOCK

    Genzyme Corporation is offering up to 1,607,400 shares of Genzyme Molecular
Oncology Division Stock, $0.01 par value per share, which we refer to as "GZMO
Stock." GZMO Stock is a series of our common stock designed to reflect the
financial performance of our Molecular Oncology division.

    We have not engaged an underwriter or placement agent to assist with this
offering. Instead, our employees will sell the shares directly to a limited
number of investors.

    We will sell the GZMO Stock for $12.91 per share. GZMO Stock is traded on
the Nasdaq National Market under the symbol "GZMO." On July 17, 2000, the last
sale price for GZMO Stock as reported by the Nasdaq was $13.6875 per share. Each
investor must purchase a minimum of 77,500 shares. The minimum investment,
consequently, is approximately $1.0 million.

    If we sell all 1,607,400 shares, we will receive gross proceeds of
approximately $20.75 million. We expect to incur approximately $30,000 in
offering expenses, regardless of the number of shares we sell. We will allocate
the net proceeds from the offering to our Molecular Oncology division.

                            ------------------------

    INVESTING IN GZMO STOCK INVOLVES SIGNIFICANT RISK. THESE RISKS ARE DESCRIBED
UNDER THE CAPTION "RISK FACTORS" BEGINNING ON PAGE 4 OF THE ACCOMPANYING
PROSPECTUS. WE RECOMMEND THAT YOU FOCUS PARTICULARLY ON "RISKS RELATED TO
GENZYME MOLECULAR ONCOLOGY" ON PAGES 16 THROUGH 18; "RISKS RELATED TO GENZYME"
ON PAGES 4 THROUGH 10; AND "RISKS RELATED TO GENZYME TRACKING STOCKS" ON PAGES
10 THROUGH 14.

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    Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus supplement and the accompanying prospectus is truthful or complete.
Any representation to the contrary is a criminal offense.

                            ------------------------

    We will terminate this offering on August 1, 2000, unless, before that date,
we sell all 1,607,400 shares.

            THE DATE OF THIS PROSPECTUS SUPPLEMENT IS JULY 17, 2000

 (This prospectus supplement replaces the prospectus supplement dated July 14,
                                     2000)

Genzyme Corporation     -    One Kendall Square    -    Cambridge, Massachusetts
02139                              -                              (617) 252-7500

                               TABLE OF CONTENTS



                                                                PAGE
                                                              --------
                                                           
PROSPECTUS SUPPLEMENT
Use of Proceeds.............................................    S-3
Plan of Distribution........................................    S-4

PROSPECTUS
Genzyme Corporation.........................................      3
Risk Factors................................................      4
Note Regarding Forward-Looking Statements...................     27
Use of Proceeds.............................................     28
Ratio of Earnings to Fixed Charges and Preferred Stock
  Dividends.................................................     28
Description of Debt Securities..............................     29
Description of Preferred Stock..............................     38
Description of Genzyme Common Stock.........................     40
Description of Warrants.....................................     52
Description of Management and Accounting Policies...........     54
Plan of Distribution........................................     59
Legal Matters...............................................     60
Experts.....................................................     60
Where You Can Find More Information.........................     61


                            ------------------------

    You should rely only on the information contained or incorporated by
reference in this prospectus supplement and the accompanying prospectus. We have
not authorized anyone to provide you with information that is different. You
should not assume that the information in this prospectus supplement, the
accompanying prospectus or any document incorporated by reference is accurate as
of any date other than the date of the applicable document. We are offering to
sell and seeking offers to buy shares of GZMO Stock only in jurisdictions where
we are permitted to make offers and sales.

                            ------------------------

    "Genzyme" is a trademark and service mark and "SAGE" is a trademark of
Genzyme. All rights reserved.

                                      S-2

                                USE OF PROCEEDS

    We estimate the net proceeds from the sale of 1,607,400 shares of GZMO Stock
in this offering would be approximately $20.75 million. We cannot assure that we
will sell all 1,607,400 shares.

    The principal purpose of this offering is to fund Genzyme Molecular
Oncology's research and preclinical and clinical development activities. We also
anticipate that the net proceeds will be used for working capital and general
corporate purposes. Genzyme Molecular Oncology may use a portion of the net
proceeds to acquire or invest in complementary businesses, joint ventures,
products or technologies. From time to time Genzyme Molecular Oncology enters
into discussions regarding acquisitions or investments. Genzyme Molecular
Oncology's management will have broad discretion to allocate the proceeds from
this offering to uses that it believes are appropriate. Pending these uses, we
currently intend to invest the net proceeds from this offering in short-term,
interest-bearing securities or deposit accounts.

                                      S-3

                              PLAN OF DISTRIBUTION

    We are selling the shares of GZMO Stock directly to a limited number of
investors. Our employees are selling the shares without the assistance of an
underwriter or placement agent. Our employees will not receive any compensation
based upon their participation in this offering and, pursuant to Rule 3a4-1 of
the Exchange Act, will not be deemed to be brokers as defined in the Exchange
Act.

    At any closing, we will deliver certificates representing the shares
purchased or effect the sale through the book entry facilities of The Depository
Trust Company, in each case against payment of the aggregate purchase price for
the shares purchased.

    We determined the per share price through oral discussions with potential
purchasers. The price represents approximately a 10% discount from the average
closing prices as reported by the Nasdaq during a trading period ending prior to
the date of this prospectus supplement.

    We expect to incur approximately $30,000 in offering expenses.

                                      S-4