PROSPECTUS SUPPLEMENT
TO PROSPECTUS DATED SEPTEMBER 18, 1998

                                                FILED PURSUANT TO RULE 424(b)(3)
                                                      REGISTRATION NO. 333-59513

                                     [LOGO]

                        $250,000,000 PRINCIPAL AMOUNT OF
                 5 1/4% CONVERTIBLE SUBORDINATED NOTES DUE 2005

           6,313,131 SHARES OF GENZYME GENERAL DIVISION COMMON STOCK

    Genzyme previously issued $250,000,000 principal amount of 5 1/4%
convertible subordinated notes due 2005. Holders of these notes can convert
principal into shares of Genzyme General Division Common Stock. This prospectus
supplement relates to sales of these notes and such shares.

    A copy of the prospectus dated September 18, 1998 should be delivered to you
together with this prospectus supplement. In deciding whether to invest, you
should carefully review the information in the prospectus and this prospectus
supplement.

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    INVESTING IN THE 5 1/4% CONVERTIBLE SUBORDINATED NOTES AND SHARES OF GENZYME
GENERAL DIVISION COMMON STOCK INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD
CAREFULLY READ AND CONSIDER THE "RISK FACTORS" BEGINNING ON PAGE 3 OF THE
PROSPECTUS.

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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 is truthful or complete. Any representation to the
contrary is a criminal offense.

           THE DATE OF THIS PROSPECTUS SUPPLEMENT IS APRIL 19, 2000.

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

                            SELLING SECURITYHOLDERS

    The information in the following table is presented as of April 18, 2000 and
supersedes in part the information in the table appearing under the heading
"Selling Securityholders" in the prospectus:



                                        PRINCIPAL AMOUNT OF    NUMBER OF SHARES    NUMBER OF SHARES OF GGD
                                        NOTES BENEFICIALLY      OF GGD STOCK+       STOCK+ ISSUABLE UPON
                                         OWNED THAT MAY BE    BENEFICIALLY OWNED   CONVERSION OF THE NOTES
NAME                                          SOLD(1)         PRIOR TO OFFERING      THAT MAY BE SOLD(2)
- ----                                    -------------------   ------------------   -----------------------
                                                                          
Goldman Sachs & Company...............        $100,000                  0                   2,525


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+   Genzyme General Division Common Stock.

(1) The notes which are offered for sale by this Prospectus represent all the
    notes held by each of the selling securityholders and less than 1% of the
    notes outstanding.

(2) Assumes conversion of the full amount of notes held by such holder at the
    initial rate of 25.2525 shares of Genzyme General Division Common Stock per
    $1,000 in principal amount of the notes. The conversion rate and the number
    of shares of Genzyme General Division Common Stock issuable upon conversion
    of the notes may be adjusted under certain circumstances. See "DESCRIPTION
    OF NOTES--Conversion Rights" beginning on page 16 of the prospectus.
    Accordingly, the number of shares of Genzyme General Division Common Stock
    issuable upon conversion of the notes may increase or decrease from time to
    time. Under the terms of Genzyme's Indenture dated May 22, 1998, fractional
    shares will not be issued upon conversion of the notes; cash will be paid
    instead of fractional shares, if any.

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