- --------------------------------------------------------------------------------
THIS IS NOT A PROXY. PLEASE DO NOT SEND IN THIS FORM WITH YOUR PROXY CARD.
INSTEAD, PLEASE RETURN THE COMPLETED FORM TO AMERICAN STOCK TRANSFER &
       TRUST COMPANY, THE EXCHANGE AGENT, IN THE ENCLOSED ENVELOPE.
- --------------------------------------------------------------------------------

                      ELECTION FORM/LETTER OF TRANSMITTAL

(TO BE COMPLETED BY HOLDERS OF COMMON STOCK OF GELTEX PHARMACEUTICALS, INC. SEE
                       ACCOMPANYING INSTRUCTION BOOKLET)

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

STEP 1: IDENTIFY YOUR SHARES AND MAKE YOUR ELECTION



- ----------------------------------------------------------------------------------------------------------------------------------
                                                                                                          
                 Name(s) and Address(es) of                     Certificate     Number of Shares     Non-       Stock      Cash
                    Registered Holder(s)                          Number*        Represented By    Election   Election   Election
- ----------------------------------------------------------------------------------------------------------------------------------

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

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

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

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

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

                                                              --------------------------------------------------------------------
                                                               Total Shares:

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


*IF YOU DO NOT HOLD GELTEX COMMON STOCK CERTIFICATES, PLEASE INDICATE AND A
BOOK-ENTRY TRANSFER WILL BE MADE FOR YOU.

YOUR ELECTION MAY BE ADJUSTED IN ACCORDANCE WITH THE TERMS OF THE MERGER
AGREEMENT. FOR FURTHER INFORMATION, SEE "THE MERGER AND THE MERGER
AGREEMENT--MERGER CONSIDERATION" ON PAGES 88 THROUGH 91 OF THE PROXY
STATEMENT/PROSPECTUS.

YOUR ELECTION WILL BE VALID ONLY IF ACCOMPANIED BY YOUR GELTEX STOCK
CERTIFICATE(S), A BOOK ENTRY TRANSFER OF SHARES TO THE EXCHANGE AGENT (CHECK THE
BOX BELOW), OR A GUARANTEE OF DELIVERY (CHECK THE BOX BELOW).

/ /  Check here if your shares of GelTex common stock are being delivered by
     book entry transfer to the exchange agent's account and complete the
     following:

       Name of Electing Institution: ___________________________________________

       The Depository Trust Company Account Number: ____________________________

       Transaction Code Number: ________________________________________________

/ /  Check here if your shares of GelTex common stock are being delivered
     pursuant to a notice of guarantee of delivery and complete the following:

       Name of Registered Holder(s): ___________________________________________

       Window Ticket Number (if any): __________________________________________

                                       THIS SPACE FOR USE OF EXCHANGE AGENT ONLY

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

STEP 2A: LETTER OF TRANSMITTAL

American Stock Transfer & Trust Company, Exchange Agent:

    In connection with the merger, the undersigned hereby submits the stock
certificate(s) representing the undersigned's shares of GelTex
Pharmaceuticals, Inc. common stock to, or hereby transfers ownership of such
stock certificate(s) by book-entry transfer to the account of, American Stock
Transfer & Trust Company, the exchange agent designated by GelTex
Pharmaceuticals, Inc. ("GelTex") and Genzyme Corporation ("Genzyme"), or its
replacement or successor, and instructs the exchange agent, following the
effective time of the merger, to deliver to the undersigned, in exchange for the
undersigned's shares of GelTex common stock, cash and/or shares of Genzyme
General Division Common Stock pursuant to the undersigned's election as set
forth on the election form enclosed with this letter of transmittal. The
undersigned understands that the undersigned's election may be adjusted pursuant
to the terms of the merger agreement.

    The undersigned also understands that the undersigned's election will not be
valid if (a) before the stockholder vote is taken on the merger, GelTex receives
written notice of the undersigned's intent to demand appraisal of the
undersigned's shares of GelTex common stock if the merger takes place and
(b) the undersigned does not vote in favor of the merger and takes other actions
as may be required prior to the effective time of the merger to perfect
dissenters' rights of appraisal under applicable law.

    The undersigned represents and warrants that the undersigned has full power
and authority to surrender the stock certificate(s) surrendered herewith or
transferred in book-entry form, or covered by a guarantee of delivery, free and
clear of all liens, claims, and encumbrances. The undersigned will, upon
request, execute and deliver any additional documents reasonably deemed by the
exchange agent or Genzyme to be appropriate or necessary to complete the sale,
assignment, or transfer of the shares of GelTex common stock. All authority
conferred or agreed to be conferred in this letter of transmittal shall be
binding upon the successors, assigns, heirs, executors, administrators, and
legal representatives of the undersigned and shall not be affected by, and shall
survive, the death or incapacity of the undersigned.

    Unless otherwise indicated under the "Special Payment Instructions" box
below, please issue any certificate for shares of Genzyme General Division
common stock and/or any check payable (or wire transfer of funds payable) in
exchange for the undersigned's shares of GelTex common stock in the name of the
registered holder(s) of such shares of GelTex common stock. Similarly, unless
otherwise indicated in the "Special Delivery Instructions" and/or "Wiring
Instructions" boxes, please mail any certificate for shares of Genzyme General
Division common stock and/or any check payable in exchange for the undersigned's
shares of GelTex common stock to the registered holder(s) of such shares of
GelTex common stock at the address or addresses shown below.

                   REGISTERED GELTEX STOCKHOLDER(S) SIGN HERE


                                                
- ------------------------------------------         ------------------------------------------
          SIGNATURE OF OWNER(S)                              SIGNATURE OF OWNER(S)

Print Name:                                        Print Name:

- ------------------------------------------         ------------------------------------------
  SOCIAL SECURITY OR OTHER TAX ID NUMBER             SOCIAL SECURITY OR OTHER TAX ID NUMBER

Address:                                           Address:

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

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

Date: , 2000                                       Date: , 2000



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

STEP 2A (CONTINUED): LETTER OF TRANSMITTAL


                SPECIAL PAYMENT INSTRUCTIONS
                                                          
(To be completed ONLY if you want the Genzyme General
Division common stock certificates and/or the cash being
issued/paid to you pursuant to the merger agreement to be
registered/payable to someone else.) IF YOU COMPLETE THIS
SPECIAL PAYMENT INSTRUCTION, YOU WILL NEED A SIGNATURE
GUARANTEE BY AN ELIGIBLE INSTITUTION.

Register my shares of Genzyme General Division common stock
and/or make payment to the following:

Name:
                   (Please type or print)

Address:

                     (include zip code)



               SPECIAL DELIVERY INSTRUCTIONS
                                                          
(To be completed ONLY if you want the Genzyme General
Division common stock certificates and/or the cash being
issued/paid to you pursuant to the merger agreement to be
registered/payable to you but sent to someone else.) IF YOU
COMPLETE THIS SPECIAL DELIVERY INSTRUCTION, YOU WILL NEED A
SIGNATURE GUARANTEE BY AN ELIGIBLE INSTITUTION.

Mail or deliver my shares of Genzyme General Division common
stock and/or send payment to the following:

Name:
                   (Please type or print)

Address:

                     (include zip code)



                      WIRING INSTRUCTIONS
                                                          
Provided I am to receive at least $500,000 in cash, I would
like all of the cash to be paid to me in connection with the
merger to be sent by wire transfer, pursuant to the
following wiring instructions in lieu of delivery of a
check:

Bank Name:
                   (Please type or print)

Bank Address:

                     (include zip code)

ABA #:
Beneficiary:
Account #:



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

STEP 2A (CONTINUED): LETTER OF TRANSMITTAL


                                          SIGNATURE GUARANTEE
                                            
(In the event that the check and/or certificate representing shares of Genzyme General Division common
stock is to be issued in exactly the name of the record holder(s) of the GelTex common stock, no
guarantee of the signature on this election form/letter of transmittal is required.)

If you have filled out either the "Special Payment Instructions" box, the "Special Delivery
Instructions" box or the "Guarantee of Delivery" box, you must have your signature(s) medallion
guaranteed by an eligible institution, i.e., a member firm of a registered national securities
exchange, a member of the NASD, Inc., or a commercial bank or trust company in the United States.

Name of Guarantor:

Signature(s) Guaranteed:

Date: , 2000

Apply Signature Medallion:



                                         GUARANTEE OF DELIVERY
                                                       
IF YOU COMPLETE THIS GUARANTEE OF DELIVERY, YOU WILL NEED A SIGNATURE GUARANTEE BY AN ELIGIBLE
INSTITUTION.

The undersigned, a member firm of a registered national securities exchange, a member of the NASD, Inc.,
or a commercial bank or trust company in the United States, hereby guarantees to deliver to the exchange
agent either all of the certificate(s) for GelTex common stock to which this election form/ letter of
transmittal relates, or such certificates as are identified below, duly endorsed in blank or otherwise
in form acceptable for transfer, no later than 12:00 noon, New York City time, on the third trading day
after the Election Deadline.

The undersigned acknowledges that it must deliver the shares of GelTex common stock covered by this
election form/letter of transmittal to the exchange agent within the time period set forth above and
that failure to do so could result in financial loss to the undersigned.

- -------------------------------------------               -------------------------------------------
Dated                                                     Printed Firm Name

- -------------------------------------------               -------------------------------------------
Certificate Number(s)                                     Authorized Signature

- -------------------------------------------               -------------------------------------------
Number of shares of GelTex common stock                   Address

                                                          -------------------------------------------
                                                          Telephone number



                                        RECEIPT OF CERTIFICATES
                                            
Unless you check the box below, you will receive book-entry shares of Genzyme General Division common
stock.

/ /  Check here if you would like certificate(s) for your shares of Genzyme General Division common
     stock.



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

STEP 2B: CERTIFY IF CERTIFICATE(S) ARE LOST

    The certificate(s) representing the following shares of GelTex common stock
has/have been lost, stolen, seized, or destroyed:


                                                   
Certificate Number                                    Shares


    (1)  I hereby certify that: (a) I have made or caused to be made a diligent
search for such stock certificate(s) and have been unable to find or recover
it/them; (b) I have not sold, assigned, pledged, transferred, deposited under
any agreement, or hypothecated the shares of GelTex Pharmaceuticals, Inc. common
stock represented by such stock certificate(s), or any interest therein, or
assigned any power of attorney or other authorization respecting the same that
is now outstanding and in force, or otherwise disposed of such stock
certificate(s); and (c) no person, firm, corporation, agency, or government,
other than me, has or has asserted any right, title, claim, equity, or interest
in, to, or respecting such shares of GelTex common stock.

    (2)  Please issue a replacement stock certificate(s). In consideration of
the issuance of a replacement certificate(s), I hereby agree to indemnify and
hold harmless Genzyme Corporation, and any person, firm, or corporation now or
hereafter acting as Genzyme Corporation's transfer agent, exchange agent,
registrar, trustee, depository, redemption, fiscal, or paying agent, or in any
other capacity, and also any successors in any such capacities, and their
respective subsidiaries, affiliates, heirs, successors, and assigns, from and
against any and all liability, loss, damage, and expense in connection with, or
arising out of, their compliance with my request herein.

    (3)  I also agree, in consideration of compliance with the foregoing
request, to surrender immediately to Genzyme Corporation the lost stock
certificate(s) should it/they hereafter come into my possession or control.


                                                   
                                                      , 2000
Signature                                             Date

                                                      , 2000
Signature                                             Date

                                                      , 2000
Signature                                             Date



                                           
STATE OF                                      )

                                              ) :ss.

COUNTY OF                                     )


    I,              , a Notary Public, do hereby certify that on the     day of
2000, personally appeared before me              , known to me to be the persons
whose name(s) is/are subscribed to the foregoing instrument, who, being by me
first duly sworn, declared that the statements contained therein are true and
that he/she/they signed said instrument for the purposes, in the capacity, and
for consideration therein expressed.

________________________________________________________________________________

(NOTARY:  PLEASE MODIFY IF NECESSARY TO CONFORM TO YOUR STATE LAW OR ATTACH AN
ALTERNATIVE FORM.)

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

STEP 3:  COMPLETE SUBSTITUTE FORM W-9


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

              SUBSTITUTE                     PART 1--PLEASE ENTER YOUR NAME              SOCIAL SECURITY NUMBER
               FORM W-9                      AND SOCIAL SECURITY NUMBER OR                         OR
                                             EMPLOYER IDENTIFICATION NUMBER              EMPLOYER IDENTIFICATION
                                                                                                 NUMBER
                                             ------------------------------------------------------------------------
         REQUEST FOR TAXPAYER                PART 2--CERTIFICATION
       IDENTIFICATION NUMBER AND             Please check the box below if you have applied for, and are awaiting
             CERTIFICATION                   receipt of, your Taxpayer Identification Number.  / /

                                             (1) The number shown on this form is my correct Taxpayer Identification
                                                 Number (or I am waiting for a number to be issued to me) and

                                             (2) I am not subject to backup withholding either because I have not been
                                                 notified by the Internal Revenue Service ("IRS") that I am subject to
                                                 backup withholding as a result of failure to report all interest or
                                                 dividends, or the IRS has notified me that I am no longer subject to
                                                 backup withholding.

    (PLEASE REFER TO THE GUIDELINES          Certificate Instructions--You may cross out item (2) in Part 2 above if you
     FOR CERTIFICATION OF TAXPAYER           have been notified by the IRS that you are subject to backup withholding
       IDENTIFICATION NUMBER ON              because of underreporting interest or dividends on your tax return.
         SUBSTITUTE FORM W-9)                However, if after being notified by the IRS that you were subject to backup
                                             withholding you received another notification from the IRS stating that you
                                             are no longer subject to backup withholding, do not cross out item (2).

                                             SIGNATURE:    DATE:
- ------------------------------------------------------------------------------------------------------------------------

PART 3--CERTIFICATION FOR FOREIGN RECORD HOLDERSUnder penalties of perjury, I certify that I am not a United States
citizen or resident (or I am signing for a foreign corporation, partnership, estate or trust).

                                                  SIGNATURE:     DATE:
- ------------------------------------------------------------------------------------------------------------------------

                                                         PART 4

Individual/Sole Proprietor  / /              Corporation  / /
Partnership  / /                             Other    / / (please specify)
- ------------------------------------------------------------------------------------------------------------------------


IF YOU CHECKED THE BOX IN PART 2 OF THE SUBSTITUTE FORM W-9, YOU MUST SIGN AND
DATE THE FOLLOWING CERTIFICATION:

         CERTIFICATION OF PAYEE AWAITING TAXPAYER IDENTIFICATION NUMBER

I certify, under penalties of perjury, that a Taxpayer Identification Number has
not been issued to me, and that I mailed or delivered an application to receive
a Taxpayer Identification Number to the appropriate IRS Center or Social
Security Administration Office (or I intend to mail or deliver an application in
the near future). I understand that if I do not provide a Taxpayer
Identification Number to the payer, 31% of all payments made pursuant to the
merger shall be retained until I provide a Taxpayer Identification Number to the
payer and that, if I do not provide my Taxpayer Identification Number within
60 days, such retained amounts shall be remitted to the IRS as backup
withholding and 31% of all reportable payments made to me thereafter will be
withheld and remitted to the IRS until I provide a Taxpayer Identification
Number.

SIGNATURE: ______________________________    DATE: _____________________________

NOTE:  FAILURE TO COMPLETE AND RETURN THIS SUBSTITUTE FORM W-9 MAY RESULT IN
       BACKUP WITHHOLDING OF 31% OF ANY PAYMENTS TO BE MADE TO YOU.

Geltex logo
153 SECOND AVENUE
WALTHAM, MASSACHUSETTS 02451

                                          NOVEMBER 15, 2000

DEAR GELTEX STOCKHOLDER:

    In connection with the merger agreement between GelTex
Pharmaceuticals, Inc. ("GelTex") and Genzyme Corporation ("Genzyme") that would
result in GelTex becoming a wholly-owned subsidiary of Genzyme, we are sending
you the enclosed election form/letter of transmittal. Once the merger is
effective, the assets, liabilities and operations of GelTex will be allocated to
Genzyme's General Division. The proposed transaction is described in greater
detail in the proxy statement /prospectus mailed to you earlier this week, and
you should carefully read the proxy statement/prospectus.

    As more fully described in the proxy statement/prospectus, if the GelTex
stockholders adopt the merger agreement and all other merger conditions are
satisfied or waived, each share of GelTex common stock will be converted into
either $47.50 in cash (the "Per Share Cash Consideration"), 0.7272 of a share of
Genzyme General Division common stock (the "Per Share Stock Consideration")
and/or a combination of cash and shares of Genzyme General Division common
stock. No fractional shares of Genzyme General Division common stock will be
issued in the merger. Instead, each GelTex stockholder who would otherwise be
entitled to receive a fractional share will receive an amount in cash, rounded
to the nearest cent, equal to the fraction multiplied by the per share value of
Genzyme General Division common stock on the trading day immediately preceding
the effective time of the merger.

    The election form/letter of transmittal offers you an opportunity to
indicate your preference for the Per Share Stock Consideration, the Per Share
Cash Consideration or to indicate that you do not have a preference (a
"Non-Election") for each share of stock you hold.

    You should complete and submit the election form/letter of transmittal, but
even if you do so, you may not receive what you elect. For further information,
see "THE MERGER AND THE MERGER AGREEMENT--Merger Consideration" in the proxy
statement/prospectus. You may revoke an election you have made by following the
instructions included in Part A.2 of the "General Instructions" to the election
form/letter of transmittal included with this letter.

    IF AMERICAN STOCK TRANSFER & TRUST COMPANY, OUR EXCHANGE AGENT, DOES NOT
RECEIVE A PROPERLY COMPLETED AND SIGNED ELECTION FORM/LETTER OF TRANSMITTAL FROM
YOU, ALONG WITH THE APPLICABLE STOCK CERTIFICATES, A BOOK ENTRY TRANSFER OF
SHARES (IF YOUR SHARES ARE HELD IN STREET NAME), OR A GUARANTEE OF DELIVERY FOR
THE SHARES OF GELTEX COMMON STOCK COVERED BY THE ELECTION FORM/LETTER OF
TRANSMITTAL BY 5:00 P.M. NEW YORK CITY TIME ON DECEMBER 8, 2000 (THE "ELECTION
DEADLINE"), THEN YOU WILL BE DEEMED NOT TO HAVE MADE A VALID ELECTION AND WILL
BE TREATED AS IF YOU HAD MADE A NON-ELECTION WITH RESPECT TO ANY SHARES OWNED BY
YOU FOR WHICH YOU HAVE FAILED TO TIMELY MAKE AN ELECTION.

    Under Delaware law, GelTex stockholders have the right to dissent from the
merger and obtain payment for the fair value of their shares of GelTex common
stock in connection with the merger. A full discussion of these dissenters'
rights of appraisal is included in the proxy statement/prospectus. See "THE
MERGER AND THE MERGER AGREEMENT--Appraisal Rights of GelTex Stockholders" and
Annex C of the proxy statement/prospectus.

    Each GelTex stockholder (other than stockholders who intend to dissent from
the merger and demand fair value for their shares under Delaware law) should
complete the election form/letter of transmittal and return it along with the
stock certificates, a book entry transfer of shares (if your shares are held in
street name), or a guarantee of delivery for the shares covered by the election
form/letter of transmittal in accordance with the instructions included in
Part A.3 of the "General Instructions" to the election form/letter of
transmittal. Please keep in mind that the method of delivery of all documents
required to make a valid election is at your option and risk, but if you choose
to submit your election form/letter of transmittal and stock certificate(s) by
mail, we suggest that you send them by registered mail, return receipt
requested, properly insured, and that you use the envelope provided with this
letter.

    As a courtesy, the exchange agent may attempt to contact any GelTex
stockholder who fails to properly comply with the election form/letter of
transmittal instructions (and who provides a phone number). However, there is no
guaranty that any such contact will be made. In any event, you are solely
responsible for properly completing and timely returning the election
form/letter of transmittal for your shares.

    If the merger is not completed for any reason, the election form/letter of
transmittal will be void and of no effect. Certificate(s) for shares of GelTex
common stock previously delivered to the exchange agent will be promptly
returned.

    Please read carefully the instructions to the election form/letter of
transmittal, then complete the information as required, sign the election
form/letter of transmittal where requested, and return the election form/letter
of transmittal, along with all of the GelTex stock certificates, book entry
transfer of shares, or guarantee of delivery of shares for which you intend to
make an election to the exchange agent no later than 5:00 p.m., New York City
time, on December 8, 2000 at the address set forth in Part A.3 of the "General
Instructions" to the election form/letter of transmittal. Delivery of the
election form/letter of transmittal to an address other than as set forth in the
General Instructions will not constitute a valid delivery.

    PLEASE REMEMBER, A COMPLETED ELECTION FORM/LETTER OF TRANSMITTAL MUST BE
RECEIVED BY THE EXCHANGE AGENT NO LATER THAN 5:00 P.M., NEW YORK CITY TIME, ON
DECEMBER 8, 2000.

                                          Sincerely,

                                          [/S/ MARK SKALETSKY]

                                          Mark Skaletsky
                                          President and Chief Executive Officer

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

                          INSTRUCTIONS FOR COMPLETING
                      ELECTION FORM/LETTER OF TRANSMITTAL

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

STEP 1: IDENTIFY YOUR SHARES AND MAKE YOUR ELECTION

    SHARE IDENTIFICATION.  You must identify the shares of GelTex common stock
that you own. In the spaces provided under the column titled "Name(s) and
Address(es) of Registered Holder(s)," print the name(s) and address(es) of the
registered holder(s). In the spaces provided under the column titled
"Certificate Number," insert the stock certificate number for each stock
certificate you hold. If you do not hold stock certificate(s), please indicate
that fact in the "Certificate Number" column. In the spaces provided under the
column titled "Number of Shares Represented By," insert the number of shares
represented by the corresponding stock certificate(s) or held in book-entry
form. At the bottom of the "Number of Shares Represented By" column, please
insert the total number of shares of GelTex common stock you are forwarding to
the exchange agent in connection with this election.

    ELECTION.  Indicate the consideration you would like to receive.

    STOCK ELECTION.  You may choose to make a stock election with respect to
some or all of your shares of GelTex common stock. To make a stock election, you
should insert the total number of shares of GelTex common stock for which you
wish to receive the Per Share Stock Consideration in the space provided under
the column titled "Stock Election."

    CASH ELECTION.  You may choose to make a cash election with respect to some
or all of your shares of GelTex common stock. To make a cash election, you
should insert the total number of shares of GelTex common stock for which you
wish to receive the Per Share Cash Consideration in the space provided under the
column titled "Cash Election."

    Non-Election.You may choose to make a Non-Election with respect to some or
all of your shares of GelTex common stock. To make a Non-Election, you should
insert the total number of GelTex shares for which you wish to make a
Non-Election in the space provided under the column titled "Non-Election."

    If the sum of your elections is less than the total number of shares of
GelTex common stock that you hold, any remaining shares will be treated as
shares for which you have made a "Non-Election."

    Any shares for which you fail to make an affirmative election or for which
you fail to properly submit this form will be deemed to have been subject to a
Non-Election.

    PLEASE REVIEW CAREFULLY "THE MERGER AND THE MERGER AGREEMENT--MERGER
CONSIDERATION" ON PAGES 88 THROUGH 91 OF THE PROXY STATEMENT/PROSPECTUS FOR AN
EXPLANATION OF THE CONVERSION OF THE SHARES OF GELTEX COMMON STOCK. AS EXPLAINED
IN THE PROXY STATEMENT/ PROSPECTUS, NOT MORE THAN 50% OF THE SHARES OF GELTEX
COMMON STOCK WILL BE EXCHANGED FOR THE RIGHT TO RECEIVE EITHER THE PER SHARE
CASH CONSIDERATION OR THE PER SHARE STOCK CONSIDERATION, AND THE TOTAL MERGER
CONSIDERATION FOR ALL SHARES OF GELTEX COMMON STOCK IS SUBJECT TO A POTENTIAL
ADJUSTMENT TO MAINTAIN THE QUALIFICATION OF THE MERGER AS A REORGANIZATION FOR
U.S. FEDERAL INCOME TAX PURPOSES. AS A RESULT, THE ACTUAL CONSIDERATION YOU
RECEIVE MAY DIFFER FROM WHAT YOU ELECT.

                              Instructions-Page 1

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

STEP 2A: LETTER OF TRANSMITTAL

    Regardless of your election in Step 1, if you are a GelTex stockholder
(other than a stockholder who intends to exercise your dissenters' rights with
respect to the merger), you must send all of the GelTex common stock
certificates, book entry transfer of shares or guarantee of delivery of shares
described in Step 1, above, to the exchange agent with the election form/letter
of transmittal. See General Instruction D.1. If you do not hold stock
certificates, please indicate that fact as described in Step 1 and a book-entry
transfer will be made for you.

    Please read page 2 of the election form/letter of transmittal.

    If you have all of the stock certificates representing the shares of GelTex
common stock described in Step 1 and do not have special payment or delivery
instructions as set forth below, sign page 2 of the election form/letter of
transmittal and go to Step 3. See General Instruction D.2. regarding the proper
form of signatures.

    If you have lost any or all of the stock certificates representing your
shares of GelTex common stock, in addition to signing the letter of transmittal
and sending it to the exchange agent together with any stock certificates you do
have as described above, you must complete Step 2B with respect to any
certificates you have lost.

    If you want any Genzyme General Division common stock certificates being
issued to you pursuant to the merger agreement to be registered in the name of,
and/or you want any cash being paid to you pursuant to the merger agreement to
be payable to, someone other than the person or entity listed on your GelTex
stock certificate, then you must complete and sign the "Special Payment
Instructions" box. If you transferred any of your shares to someone else after
October 24, 2000, you must complete and sign the "Special Payment Instructions"
box. See General Instruction D.7 for information about your responsibility for
transfer taxes if you complete the "Special Payment Instructions" box.

    If you want the Genzyme General Division common stock certificates or book
entry and/or the cash being issued or paid to you pursuant to the merger to be
registered or payable to you, but sent to someone else, you must complete and
sign the "Special Delivery Instructions" box.

    IF YOU FILL OUT EITHER THE "SPECIAL PAYMENT INSTRUCTIONS" BOX OR THE
"SPECIAL DELIVERY INSTRUCTIONS" BOX, YOU MUST HAVE YOUR SIGNATURE(S) MEDALLION
GUARANTEED BY AN ELIGIBLE INSTITUTION. SEE GENERAL INSTRUCTION D.4.

    If your cash payment is at least $500,000 and you would like it to be sent
to you by wire transfer rather than by check, you must complete and sign the
"Wiring Instructions" box. Please verify your wiring instructions before
completing the "Wiring Instructions" box. If you provide incorrect wiring
instructions, the exchange agent will have the right to send your money to you
by check.

    If your GelTex stock certificates are not deliverable to the exchange agent
prior to 5:00 p.m., New York City time, on December 8, 2000 (the "Election
Deadline"), a guarantee of delivery may be completed by an eligible institution
and your election will be valid if the exchange agent receives the completed
election form/letter of transmittal prior to the Election Deadline and the stock
certificates no later than 12:00 noon, New York City time, on December 13, 2000,
the third trading day after the Election Deadline.

    The exchange agent will issue you a single check and/or a single book entry
representing Genzyme General Division common stock. If you would prefer to
receive a stock certificate, please check the box in the "Receipt of
Certificates" section. If you request a stock certificate, the exchange agent
will issue a single certificate representing the Genzyme General Division common
stock. However, if for tax purposes or otherwise you wish to have more than one
certificate issued, please provide explicit instructions to the exchange agent
(including the particular denominations of the certificates).

                              Instructions-Page 2

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

STEP 2B: CERTIFY IF CERTIFICATE(S) ARE LOST

    If you are unable to locate some or all of the stock certificates
representing your shares of GelTex common stock, you must complete the
certification on page 5 of the election form/letter of transmittal. Your
signature must be notarized.

    Please see General Instruction D.2 regarding proper signatures.

    After you have completed Step 2B, go to Step 3.

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

STEP 3: COMPLETE SUBSTITUTE FORM W-9

    GelTex stockholders must complete the Substitute Form W-9 on page 6 of the
election form/ letter of transmittal to avoid having 31% of any cash payment
withheld for federal income tax purposes as set forth in General
Instruction D.6 to this form.

    Please do the following:

(1) write your name and social security number (or employer identification
    number for entities) in Part I of the Substitute Form W-9;

(2) check the box next to "Individual/Sole Proprietor," "Corporation,"
    "Partnership" or "Other" (and, if other, write in the type of entity); and

(3) sign the "Certification" box in Part 2 of the Substitute Form W-9.

    If you do not yet have a Taxpayer Identification Number, please check the
box in "Part 2" and sign the "Certification of Payee Awaiting Taxpayer
Identification Number" box at the bottom of that page.

    Please see General Instruction D.6 for information on the Form W-9 and
General Instruction D.2 regarding proper signatures.

                              Instructions-Page 3

                              GENERAL INSTRUCTIONS

A.  SPECIAL CONDITIONS.

    1.  TIME IN WHICH TO ELECT. To be effective, a completed election
form/letter of transmittal and your GelTex common stock certificate(s), a book
entry transfer of shares, or a guarantee of delivery for the shares covered by
the election form/letter of transmittal, must be received by the exchange agent
no later than the Election Deadline. If the merger is approved and thereafter
completed, and if the exchange agent has not received a properly completed
election form/letter of transmittal prior to the Election Deadline for any
shares owned by you, you will be deemed to have made a Non-Election with respect
to all shares for which a valid election has not been made.

    2.  REVOCATION OF ELECTION. An election may be revoked only by the person
who submitted the election form/letter of transmittal to the exchange agent by
written notice to the exchange agent, or by withdrawal of the shares of GelTex
common stock deposited by such person with the exchange agent, prior to the
Election Deadline. You may submit a new election form at the time you revoke an
earlier election or at any time after revoking an earlier election but before
the Election Deadline. If the merger agreement is terminated, all election
forms/letters of transmittal will automatically be revoked and the stock
certificates tendered will be promptly returned.

    3.  DELIVERY INSTRUCTIONS. Each GelTex stockholder (other than stockholders
who intend to dissent from the merger and demand fair value for their shares
under Delaware law) should complete the election form/letter of transmittal and
return it along with the stock certificates, a book entry transfer of shares (if
your shares are held in street name), or a guarantee of delivery for the shares
covered by the election form/letter of transmittal to: AMERICAN STOCK
TRANSFER & TRUST COMPANY

BY MAIL:

    GELTEX PHARMACEUTICALS, INC.
    c/o American Stock Transfer & Trust Company
    59 Maiden Lane
    New York, NY 10038

BY FACSIMILE TRANSMISSION (FOR ELIGIBLE INSTITUTIONS ONLY): (718) 234-5001

CONFIRM BY TELEPHONE: (800) 937-5449 ext. 6820 (if calling from beyond the 718
area code)
                   (718) 921-8200 ext. 6820 (if calling from within the 718 area
code)

B.  ELECTION PROCEDURES.

    A description of the election procedures is contained in the proxy
statement/prospectus under "THE MERGER AND THE MERGER AGREEMENT--Procedure for
Filing Elections" and is fully set forth in the merger agreement. All elections
are subject to compliance with those procedures. Before making any election, you
should read carefully, among other matters, the information contained in the
proxy statement/prospectus under "THE MERGER AND THE MERGER AGREEMENT--Material
United States Federal Income Consequences Of The Merger" and under "RISK
FACTORS--Risks Relating to the Merger."

    In accordance with the terms of the merger agreement, you may receive shares
of Genzyme General Division common stock and/or cash in amounts that vary from
your election in Step 1 of the election form/letter of transmittal. You will not
be able to change the number of shares or the amount of cash allocated to you by
the exchange agent pursuant to the election procedures.

                              Instructions-Page 4

C.  RECEIPT OF SHARES OR CASH.

    Promptly after the effective time of the merger, Genzyme will instruct the
exchange agent to mail certificate(s) or effect a single book entry representing
your shares of Genzyme General Division common stock and/or cash payments by
check to you or as you otherwise instruct in this election form/letter of
transmittal (if you complete the "Wiring Instructions" in Step 2A of this form
and you are to receive at least $500,000, cash will be sent to you by wire
transfer). If you fail to submit a properly completed election form/letter of
transmittal and stock certificates, a book entry transfer of shares, or a
guarantee of delivery for the shares of GelTex common stock covered by the
election form/letter of transmittal by the Election Deadline as set forth above,
you will be deemed to have made a Non-Election and will be entitled to receive
the applicable merger consideration, after the certificate(s) representing such
shares of GelTex common stock have been submitted.

    No fractional shares of Genzyme General Division common stock will be issued
in the merger. Instead, each GelTex stockholder that otherwise would be entitled
to receive a fractional share will receive an amount in cash equal to that
fraction multiplied by the per share value of the Genzyme General Division
common stock as determined prior to the effective time of the merger in
accordance with the terms of the merger agreement.

D.  GENERAL.

    1.  EXECUTION AND DELIVERY. This election form/letter of transmittal must be
properly filled in, dated, and signed in all applicable places, and must be
delivered (together with all of the other required materials) to the exchange
agent at the address set forth above. The method of delivery of all documents is
at your option and risk, but if you choose to return your materials by mail, we
suggest you send them by registered mail, return receipt requested, properly
insured, using the enclosed envelope.

    2.  SIGNATURES. The signature (or signatures, in the case of certificates
owned by two or more joint holders) on the election form/letter of transmittal
should correspond exactly with the name(s) as written on the face of the
certificate(s) submitted unless the shares of GelTex common stock described on
the election form/letter of transmittal have been assigned by the registered
holder(s), in which event this form should be signed in exactly the same form as
the name of the last transferee indicated on the transfers attached to or
endorsed on the certificates.

    If the election form/letter of transmittal is signed by a person or persons
other than the registered holder(s) of the certificates, the certificates must
be endorsed or accompanied by appropriate stock powers, in either case signed
exactly as the name(s) of the registered owner(s) appears on the certificates.

    If the election form/letter of transmittal or any stock certificate(s) or
stock power(s) is signed by a trustee, executor administrator, guardian, officer
of a corporation, attorney-in-fact, or any other person acting in a
representative or fiduciary capacity, the person signing must give the signing
person's full title in such capacity.

    3.  NEW CERTIFICATES AND CHECKS IN SAME NAME. If you are receiving any
shares of Genzyme General Division common stock, the stock certificate(s)
representing such shares of Genzyme General Division common stock and/or any
check(s) in respect of shares of GelTex common stock shall be registered in, or
payable to the order of, exactly the same name(s) that appears on the
certificate(s) representing such shares of GelTex common stock submitted with
the election form/ letter of transmittal, unless the "Special Payment
Instructions" box in Step 2A of the form is completed. No endorsement of
certificate(s) or separate stock power(s) is required.

    4.  GUARANTEE OF SIGNATURE. No signature guarantee is required on the
election form/letter of transmittal if it is signed by the registered holder(s)
of the shares of GelTex common stock surrendered under the form, and the shares
of Genzyme General Division common stock and/or the check are to be issued
and/or payable to the record holder(s) without any change or correction in

                              Instructions-Page 5

the name of the record holder(s). In all other cases, all signatures on the
election form/letter of transmittal must be guaranteed. All signatures required
to be guaranteed must be guaranteed by a member firm of a registered national
securities exchange or of the NASD, Inc., or a commercial bank or trust company
in the United States. Public notaries cannot execute acceptable guarantees of
signatures. Contact your broker to determine if they can provide such a
guarantee.

    5.  MISCELLANEOUS. A single check, or wire transfer, and/or stock
certificate or a single book entry representing shares of Genzyme General
Division common stock to be received will be issued to you unless you have
instructed us otherwise in the election form/letter of transmittal.

    All questions with respect to the election form/letter of transmittal
(including, without limitation, questions relating to the timeliness or
effectiveness of any election or the revocation of any election, and
computations as to any adjustments) will be determined by the exchange agent,
which determination shall be conclusive and binding.

    6.  BACKUP FEDERAL INCOME TAX WITHHOLDING AND SUBSTITUTE FORM W-9. Under the
"backup withholding" provisions of U.S. federal income tax law, any payments
made to you pursuant to the merger may be subject to backup withholding of 31%.
To prevent backup withholding, GelTex stockholders must complete and sign the
Substitute Form W-9 included in Step 3 of the election form/letter of
transmittal and either (a) provide your correct taxpayer identification number
("TIN") and certify, under penalties of perjury, that the TIN provided is
correct (or that you are awaiting a TIN), and that (i) you have not been
notified by the IRS that you have been subjected to backup withholding as a
result of failure to report all interest or dividends or (ii) the IRS has
notified you that you are no longer subject to backup withholding; or
(b) provide an adequate basis for exemption. If the bottom portion of the
Substitute Form W-9 is signed as indicating that you are awaiting a TIN, the
exchange agent will retain 31% of cash payments made to you during the 60 day
period after the date of the Substitute Form W-9. If you furnish the exchange
agent with your TIN within 60 days of the date of the Substitute Form W-9, the
exchange agent will remit those withheld amounts retained during this 60-day
period to you. If, however, you have not provided the exchange agent with your
TIN within this 60-day period, the exchange agent will remit these previously
retained amounts to the IRS as backup withholding. In general, if you are an
individual, the TIN is your social security-number. If the certificates for
GelTex common stock are registered in more than one name or are not in the name
of the actual owner, consult the Guidelines for Certification of Taxpayer
Identification Number on Substitute Form W-9 (copies of which may be obtained
from the exchange agent) for additional guidance on which number to report. If
the exchange agent is not provided with the correct TIN or an adequate basis for
exemption, the holder may be subject to a $50 penalty imposed by the IRS and
backup withholding at a rate of 31%. Certain stockholders (including, among
others, all corporations and certain foreign individuals) are not subject to
these backup withholding and reporting requirements. In order to satisfy the
exchange agent that a foreign individual qualifies as an exempt recipient, such
holder must submit a statement (generally, IRS Form W-8), signed under penalties
of perjury, attesting to that individual's exempt status. A form for this
statement can be obtained from the exchange agent.

    For further information concerning backup withholding and instructions for
completing the Substitute Form W 9 (including how to obtain a TIN if you do not
have one and how to complete the Substitute Form W-9 if stock is held in more
than one name), consult the Guidelines for Certification of Taxpayer
Identification Number on Substitute Form W-9 (copies of which may be obtained
from the exchange agent).

    Failure to complete the Substitute Form W-9 will not, by itself, cause your
shares of GelTex common stock to be deemed invalidly tendered, but may require
the exchange agent to withhold 31% of the amount of any payments made pursuant
to the merger. Backup withholding is not an additional U.S. federal income tax.
Rather the U.S. federal income tax liability of a person subject to backup
withholding will be reduced by the amount of tax withheld. If withholding
results in an overpayment of taxes, a refund may be obtained from the IRS.

    7.  TRANSFER TAXES. If you completed the "Special Payment Instructions" box
in Step 2A, you must pay the exchange agent any and all required transfer or
other taxes or must establish that these taxes have been paid or are not
applicable.

                              Instructions-Page 6