EXHIBIT 99.2

                                   FOCAL, INC.
                                 4 MAGUIRE ROAD
                               LEXINGTON, MA 02421

                                                     April 25, 2001


Genzyme Corporation
One Kendall Square
Cambridge, MA  02139
Attention: Earl M. Collier, Jr.

Dear Duke:

         This letter agreement sets forth our understanding with respect to
certain matters relating to (x) the obligation of Genzyme Corporation
("Genzyme") to purchase from Focal, Inc. ("Focal"), at Focal's option, up to
$5.0 million of Focal's Common Stock, $0.01 par value per share, pursuant to the
terms of Section 1.2(a)(iii) of the Stock Purchase Agreement dated October 21,
1999 by and between Focal and Genzyme (the "Stock Purchase Agreement"), and (y)
the Distribution and Marketing Collaboration Agreement dated October 21, 1999
between Genzyme and Focal (the "Distribution and Marketing Agreement").
Capitalized terms used herein which are not otherwise defined are used with the
meanings ascribed thereto in the Stock Purchase Agreement.

         Now therefore, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, Focal and Genzyme hereby agree as
follows:

1.  Notwithstanding anything to the contrary contained in Section 1.2(a)(iii) of
    the Stock Purchase Agreement, subject to the following sentence, the Third
    Option Purchase Price on any Purchase Date (as defined below) shall mean (i)
    $0.70 per share, or (ii) if the Common Stock ceases to be listed on the
    Nasdaq National Market prior to such Purchase Date, $0.40 per share. If the
    Agreement and Plan of Merger by and among Genzyme, Focal and a wholly-owned
    subsidiary of Genzyme dated as of date hereof (the "Merger Agreement") is
    terminated prior to June 15, 2001, the Third Option Purchase Price shall
    mean the average of the per share regular 4:00 p.m. eastern time closing
    prices of the Common Stock as reported by the Nasdaq National Market (or if
    the Common Stock is not then listed on the Nasdaq National Market, on the
    principal trading market for the Common Stock at that time, or, if there is
    no principal trading market, the fair market value per share of Common Stock
    as determined in good faith by the Board of Directors of the Company) for
    the five consecutive trading days immediately preceding the applicable
    Purchase Date.

2.  None of (1) the execution and delivery of the Merger Agreement, and
    consummation of the transactions contemplated thereby prior to the Effective
    Time (as defined in Merger Agreement), (2) the modification of the Marketing
    and Distribution Agreement as discussed below, (3) any termination of the
    Merger Agreement, (4) the Nasdaq National



Genzyme Corporation
April 25, 2001
Page 2

    Market ceasing to list the Common Stock and (5) any public announcement
    relating to the foregoing, shall be deemed to constitute a cause to
    terminate the Stock Purchase Agreement pursuant to Section 1.2(e) or a
    failure of a condition to closing of the Third Option, or otherwise affect
    Genzyme's obligation to purchase the Shares upon Focal's exercise of the
    Third Option.

3.  All information contained in the Merger Agreement, this letter, and the
    Company Disclosure Schedule (as defined in the Merger Agreement) and any
    actions taken by the parties in accordance with the Merger Agreement shall
    be deemed to constitute exceptions to the representations and warranties and
    other provisions in the Stock Purchase Agreement for purposes of determining
    whether the conditions to the exercise of the Third Option have been
    satisfied.

4.  Notwithstanding the terms of the Stock Purchase Agreement, (i) the Exercise
    Notice for the Third Option may be delivered by Focal at any time during the
    period beginning on June 15, 2001 and ending on July 12, 2001, and (ii) the
    Third Option Closing and the transfer of Shares pursuant to the exercise of
    the Third Option shall occur as follows (with no potential delay due to the
    occurrence of a Material Event):

    (i)     on July16, 2001, Genzyme shall purchase the number of Third Option
            Shares determined by dividing (x) 25% of the aggregate exercise
            amount by (y) the purchase price applicable on such purchase date,
            rounded to the nearest whole share;

    (ii)    on July 31, 2001, Genzyme shall purchase the number of Third Option
            Shares determined by dividing (x) 25% of the aggregate exercise
            amount by (y) the purchase price applicable on such purchase date,
            rounded to the nearest whole share;

    (iii)   on August 15, 2001, Genzyme shall purchase the number of Third
            Option Shares determined by dividing (x) 25% of the aggregate
            exercise amount by (y) the purchase price applicable on such
            purchase date, rounded to the nearest whole share; and

    (iv)    on August 31, 2001, Genzyme shall purchase the balance of the Third
            Option Shares.

         July 16, July 31, August 15 and August 31, 2001 are referred to herein
         individually as a "Purchase Date" and collectively, as the "Purchase
         Dates."

5.  Notwithstanding the foregoing and anything to the contrary in the Stock
    Purchase Agreement, Genzyme's obligation to purchase the Third Option Shares
    shall be determined as of June 15, 2001. If the conditions (other than
    deliveries of notices and other documents) to Genzyme's obligation to
    purchase the Third Option Shares, as modified by



Genzyme Corporation
April 25, 2001
Page 3

    this letter agreement, are satisfied as of June 15, 2001, thereafter all
    conditions to Genzyme's obligation to purchase the Third Option Shares shall
    be waived except (i) the conditions in Section 5.2(a)(iii)(3) and (4) of the
    Stock Purchase Agreement and (ii) the receipt of the documents specified in
    Article VI of the Stock Purchase Agreement (which, to the extent such
    document refers to matters other than the conditions specified in (i), may
    refer to the status of circumstances known as of June 15, 2001 and may
    expressly disclaim any reference to any circumstance arising after such
    date).

6.  The second bullet point in Exhibit B of the Distribution and Marketing
    Agreement is hereby deleted in its entirety and a new bullet point is
    inserted in lieu thereof which reads as follows:

    "o  GSP will employ a cardiac sales group of at least twenty (20)
        individuals in the US market that will sell FocalSeal(R)-L product as
        one of its primary products. Focal will employ a dedicated thoracic
        promotional group of at least two (2) individuals to co-promote the same
        product within a reasonable time after System Launch."

7.  The amendment to the Distribution and Marketing Agreement set forth in
    paragraph 6 above shall not constitute a Material Event, and shall in no way
    affect Genzyme's obligation to purchase the Shares upon Focal's exercise of
    the Third Option.

8.  From the date of this Agreement through the earliest of (x) September 1,
    2001, (y) the date the Merger Agreement becomes terminable by Genzyme
    pursuant to Section 8.1(c) of the Merger Agreement, or (z) the termination
    of the Merger Agreement in accordance with its terms, Genzyme agrees that
    (i) Genzyme will not sell, transfer or otherwise dispose of beneficial
    ownership of shares of Common Stock, (ii) in no event will Genzyme acquire
    beneficial ownership or voting rights with respect to shares of the Common
    Stock other than pursuant to (1) exercise of the Third Option under the
    Stock Purchase Agreement, (2) exercise of Genzyme's rights under Section 7.1
    the Stock Purchase Agreement or (3) the terms of the Merger Agreement and
    the Voting Agreements (as defined in the Merger Agreement), and (iii) at any
    meeting of Focal's stockholders, unless otherwise requested by Focal,
    Genzyme shall ensure that no votes are cast nor proxies given with respect
    to the Excess Number (as defined below) of shares of Focal's Common Stock as
    to which Genzyme has beneficial ownership or voting rights. In the event
    Genzyme acquires beneficial ownership or voting rights with respect to an
    aggregate number of shares of Focal's Common Stock representing 40% or more
    of the number of outstanding shares of Focal's Common Stock as of the record
    date for any meeting of Focal's stockholders, the number of shares exceeding
    40% of such number of outstanding shares of Focal's Common Stock shall be
    referred to as the Excess Number.

9.  While the Merger Agreement is in effect, sections 4.1(b)(iv) and 4.10 of the
    Merger Agreement shall govern in lieu of Sections 7.1 and 8.4 of the Stock
    Purchase Agreement.



Genzyme Corporation
April 25, 2001
Page 4

10. Except as specifically set forth herein, the Stock Purchase Agreement and
    Distribution and Marketing Agreement shall each remain in full force and
    effect and are hereby ratified and confirmed in all respects.



Genzyme Corporation
April 25, 2001
Page 5

         Please countersign this letter in the space provided below to indicate
your agreement with the foregoing.

                                     Very truly yours,

                                     FOCAL, INC.

                                     By: /s/ Ronald Rudowsky
                                         --------------------------------------
                                         Ronald Rudowsky, President

AGREED:

GENZYME CORPORATION

By: /s/ Earl M. Collier, Jr.
    ---------------------------------
    Earl M. Collier, Jr.,
    Executive Vice President