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                                                                   Exhibit 10.18

                               GENZYME CORPORATION
                           2004 EQUITY INCENTIVE PLAN

1.   PURPOSE

          The 2004 Equity Incentive Plan (the "Plan") has been established to
promote the interests of the Company and its shareholders by strengthening the
Company's ability to attract, motivate, and retain key employees and consultants
of the Company and its Affiliates upon whose judgment, initiative, and efforts
the financial success and growth of the business of the Company largely depend.
The Plan is intended to provide an additional incentive for such individuals
through stock ownership and other rights that promote and recognize the
financial success and growth of the Company and create value for shareholders.
Certain capitalized terms used herein and certain operating rules related
thereto are defined and set forth in Section 10 below.

          The Plan provides for the grant of Stock Options, including ISOs and
NSOs.

          The Plan shall become effective upon shareholder approval (the
"Effective Date") and unless sooner terminated, shall terminate ten years from
the Effective Date. After the Plan is terminated, no Stock Options may be
granted, but Stock Options previously granted shall remain outstanding in
accordance with their applicable terms and conditions and the Plan's terms and
conditions.

2.   ADMINISTRATION

          The Compensation Committee shall be the Administrator of the Plan
except as hereinafter provided. The Compensation Committee may delegate to one
or more of its members such of its duties, powers and responsibilities as it may
determine. To the extent determined by the Compensation Committee and permitted
by applicable law, the Compensation Committee may also delegate to one or more
executive officers of the Company the power to grant Stock Options to, or
allocate Stock Options among, Participants who are not Reporting Persons or
Covered Employees and to make such determinations under the Plan with respect
thereto as the Compensation Committee determines. The Compensation Committee may
also delegate to such Employees or other persons as it determines such
ministerial tasks as it deems appropriate. In the event of any delegation
described in this paragraph, the term "Administrator" shall include the person
or persons so delegated to the extent of such delegation.

          The Administrator has discretionary authority, subject only to the
express provisions of the Plan, to interpret the Plan; determine eligibility for
and grant Stock Options; select the Participants to receive Stock Options and
determine, modify or waive the terms and conditions of any Stock Option;
prescribe forms, rules and procedures; and otherwise do all things necessary to
carry out the purposes of the Plan. The terms of each Stock Option grant need
not be identical, and the Administrator need not treat Participants uniformly.
Except as otherwise provided by the Plan or a particular Stock Option, any
determination with respect to a Stock Option may be made by the Administrator at
the time of grant or at any time thereafter. In the case of any Stock Option
intended to be eligible for the performance-based compensation exception under
Section 162(m), the Administrator will exercise its discretion consistent with
qualifying the Stock Option for that exception. Determinations made by the
Administrator shall be final and binding upon Participants, the Company, and all
other interested parties.

     3.   STOCK AVAILABLE FOR GRANT; LIMITS

          (a) NUMBER OF SHARES. Subject to adjustment as provided under
Section 6, the maximum number of shares available for issuance to
Participants under the Plan shall be 6,800,000 shares of ISOs. Subject to
such overall maximum, up to 6,800,000 shares of Stock may be issued upon the
exercise of ISOs and up to 6,800,000 shares of Stock may be issued upon
exercise of NSOs. Stock delivered by the

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Company under the Plan may be authorized but unissued Stock or previously issued
Stock acquired by the Company. No fractional shares of Stock will be delivered
under the Plan. To the extent consistent with the requirements of Section 422 of
the Code, and with other applicable legal requirements (including applicable
NASDAQ or stock exchange requirements), Stock issued under option grants of an
acquired company that are assumed in connection with the acquisition, or under
Stock Options issued in substitution for options of an acquired-company, shall
not reduce the number of shares available for issuance under the Plan.

          (b) SECTION 162(m) LIMITS. The maximum number of shares of Stock for
which Stock Options may be granted to any person in any calendar year will be
2,000,000. The foregoing provision will be construed in a manner consistent with
Section 162(m).

4.   ELIGIBILITY AND PARTICIPATION

          All employees and consultants of the Company or any Affiliate capable
of contributing significantly to the successful performance of the Company,
other than a person who has irrevocably elected not be eligible, are eligible to
be Participants in the Plan. Eligibility for ISOs is limited to employees of the
Company or of a "parent corporation" or "subsidiary corporation" of the Company
as those terms are defined in Section 424 of the Code. The Administrator, in its
sole discretion, shall determine from the group of eligible persons whether an
individual shall be a Participant under the Plan. Any grant made under the Plan
shall be made in the sole discretion of the Administrator and no prior grant
shall entitle a person to any future grant.

5.   RULES APPLICABLE TO STOCK OPTIONS

     (a) DOCUMENTATION. Each Stock Option granted under the Plan shall be
evidenced by a writing specifying the terms and conditions thereof and
containing such other terms and conditions not inconsistent with the provisions
of the Plan as the Administrator considers necessary or advisable to achieve the
purposes of the Plan or to comply with applicable tax and regulatory laws and
accounting principles.

     (b) TRANSFERABILITY. In the discretion of the Administrator, any Stock
Option may be made transferable upon such terms and conditions and to such
extent as the Administrator determines, provided that ISOs may not be
transferred other than by will or by the laws of descent and distribution. Any
non-transferable Stock Option requiring exercise, including any ISO, may be
exercised only by the Participant during the Participant's lifetime. The
Administrator may in its discretion, other than in the case of Stock Options
intended to continue to qualify as ISOs, waive any restriction on
transferability.

     (c) VESTING; EXERCISABILITY. The Administrator shall determine the time or
times at which a Stock Option will vest or become exercisable and the terms on
which a Stock Option will remain exercisable during or following termination of
Employment. Without limiting the foregoing, the Administrator may at any time
accelerate the vesting or exercisability of a Stock Option, regardless of any
adverse or potentially adverse tax consequences resulting from such
acceleration.

     (d) TAXES. The Participant shall pay to the Company, or make provision
satisfactory to the Administrator for payment of, any taxes required by law to
be withheld in respect of Stock Options granted under the Plan no later than the
date of the event creating the tax liability. The Company and its Affiliates
may, to the extent permitted by law, deduct any such tax obligations from any
payment of any kind due to the Participant hereunder or otherwise. In the
Administrator's discretion, the minimum tax obligations required by law to be
withheld in respect of Stock Options may be paid in whole or in part in shares
of Stock, including shares retained from the event creating the tax obligation,
valued at their Fair Market Value on the date of retention or delivery.

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     (e) DIVIDEND EQUIVALENTS, ETC. The Administrator may provide for the
payment of amounts in lieu of cash dividends or other cash distributions with
respect to Stock subject to a Stock Option.

     (f) RIGHTS LIMITED. Nothing in the Plan will be construed as giving any
person the right to continued employment or service with the Company or its
Affiliates, or any rights as a shareholder except as to shares of Stock actually
issued under the Plan. In no event shall the Plan, or any grant made under the
Plan, form a part of an employee's or consultant's contract of employment or
service, if any. The loss of existing or potential profit in Stock Options will
not constitute an element of damages in the event of termination of employment
or service for any reason, even if the termination is in violation of an
obligation of the Company or Affiliate to the Participant.

     (g) NON-U.S. STOCK OPTIONS. Stock Options may be granted under the Plan to
any eligible person regardless of the jurisdiction in which he or she works or
resides. In order to comply with the laws in other countries in which the
Company operates, the Administrator, in its sole discretion, shall have the
power and authority to:

         (i) Establish one or more separate sub-plans or programs under the Plan
         for the grant of Stock Options to eligible persons in a specified
         jurisdiction or jurisdictions;

         (ii) Include in any such sub-plan or program such special rules as it
         determines to be necessary or advisable; and

         (iii) Take any action, before or after a Stock Option grant is made,
         that it deems advisable to obtain approval or comply with any necessary
         local government regulatory exemptions or approvals.

Notwithstanding the above, the Administrator may not take any actions hereunder,
and no Stock Options shall be granted, that would violate applicable law.

     (h) EXERCISE PRICE. The exercise price of a Stock Option will not be less
than 100% of the Fair Market Value of the Stock on the date of grant.
Notwithstanding the foregoing sentence, a NSO may be granted to a new employee
or consultant in connection with the hiring of such person at a lower exercise
price, provided that it is not less than the lower of (i) 100% of the Fair
Market Value on the date the person accepts the Company's offer of employment or
(ii) the date employment commences. Once granted, no Stock Option may be
repriced (as that term is used under applicable NASDAQ or stock exchange rules)
without shareholder approval.

     (i) TIME AND MANNER OF EXERCISE. Unless the Administrator expressly
provides otherwise, a Stock Option will not be deemed to have been exercised
until the Company receives a notice of exercise (in a form acceptable to the
Administrator) signed by the appropriate person and accompanied by payment of
the exercise price. If the Stock Option is exercised by any person other than
the Participant, the Administrator may require satisfactory evidence that the
person exercising the Stock Option has the right to do so. All Stock Options
granted pursuant to the Plan shall terminate if not exercised within ten years
of the date of grant, or such earlier date as the Administrator may determine.

     (j) PAYMENT. No shares shall be delivered pursuant to any exercise of a
Stock Option until payment in full of the exercise price therefore is received
by the Company. Such payment may be made in whole or in part in cash or, to the
extent permitted by the Administrator at or after the grant of the Stock Option,
in shares of Stock owned by the Participant (which shares must be owned for at
least six months) valued at their Fair Market Value on the date of delivery, or
such other lawful consideration, including use of a broker-assisted exercise
program or similar program, as the Administrator may determine. The delivery of
shares in payment of the exercise

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price may be accomplished either by actual delivery or by constructive delivery
through attestation of ownership, subject to such rules as the Administrator may
prescribe.

6.   EFFECT OF CERTAIN TRANSACTIONS

   (a) COVERED TRANSACTIONS. Except as otherwise provided under the terms of a
Stock Option grant, in the event of a Covered Transaction in which there is an
acquiring or surviving entity, the Administrator may provide for the assumption
of some or all outstanding Stock Options, or for the grant of new Stock Options
in substitution therefor, by the acquiror or survivor or an affiliate of the
acquiror or survivor, in each case on such terms and subject to such conditions
as the Administrator determines. In the absence of such an assumption or if
there is no substitution, except as otherwise provided in the Stock Option, each
Stock Option will become fully exercisable, prior to the Covered Transaction so
as to give the holder of the Stock Option a reasonable opportunity, as
determined by the Administrator, following exercise of the Stock Option to
participate as a shareholder in the Covered Transaction, and the Stock Option
will terminate upon consummation of the Covered Transaction. Without limiting
the general scope of the Administrator's discretionary authority under the Plan,
the Administrator may provide, as to some or all Stock Options, if any, that in
the event of a Change in Control of the Company, whether or not such Change in
Control is also a Covered Transaction, the vesting and exercisability of, or the
payment of benefits under, any Stock Option will be accelerated on such terms as
the Administrator determines.

   (b) DISTRIBUTIONS; CHANGES IN CAPITAL STOCK. Basic Adjustment Provisions. In
the event of a stock dividend, stock split (including reverse stock split) or
combination of shares, recapitalization or other change in the Company's capital
structure, the Administrator will make appropriate adjustments to the maximum
number of shares specified in Section 3(a) that may be delivered under the Plan,
to the maximum number of shares specified in Section 3(a) that may be issued
upon the exercise of ISOs, to the maximum number of shares specified in Section
3(a) that may be issued upon exercise of NSOs, and to the maximum share limits
described in Section 3(b). The Administrator will also make appropriate
adjustments to the number and kind of shares of stock or securities subject to
Stock Options then outstanding or subsequently granted, any exercise prices
relating to Stock Options and any other provision of the Stock Options affected
by such change.

   (c) CERTAIN OTHER ADJUSTMENTS. To the extent consistent with qualification of
ISOs under Section 422 of the Code and with the performance-based compensation
rules of Section 162(m), where applicable, the Administrator may also make
adjustments of the type above to take into account distributions to shareholders
other than those provided for in Section 6(a), or any other event, if the
Administrator determines that adjustments are appropriate to avoid distortion in
the operation of the Plan and to preserve the value of Stock Option grants made
hereunder.

   (d) CONTINUING APPLICATION OF PLAN TERMS. References in the Plan to shares of
Stock will be construed to include any stock or securities resulting from an
adjustment pursuant to this Section 6.

7.   LEGAL CONDITIONS ON DELIVERY OF STOCK

          The Company will not be obligated to deliver any shares of Stock
pursuant to the Plan or to remove any restriction from shares of Stock
previously delivered under the Plan until: (i) the Company is satisfied that all
legal matters in connection with the issuance and delivery of such shares have
been addressed and resolved; (ii) if the outstanding Stock is at the time of
delivery listed on any stock exchange or national market system, the shares to
be delivered have been listed or authorized to be listed on such exchange or
system upon official notice of issuance; and (iii) all conditions of the grant
have been satisfied or waived. If the sale of Stock has not been registered
under the Securities Act of 1933, as amended, the Company may require, as a
condition to exercise of the Stock Option, such representations or agreements as
counsel for the

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Company may consider appropriate to avoid violation of such Act. The Company may
require that certificates evidencing Stock issued under the Plan bear an
appropriate legend reflecting any restriction on transfer applicable to such
Stock.

8.   AMENDMENT AND TERMINATION

          The Administrator may at any time or times amend the Plan or any
outstanding Stock Option for any purpose which may at the time be permitted by
law, and may at any time terminate the Plan as to any future grants of Stock
Options; PROVIDED, that except as otherwise expressly provided in the Plan the
Administrator may not, without the Participant's consent, alter the terms of a
Stock Option so as to affect adversely a Participant's rights under the Stock
Option, unless the Administrator expressly reserved the right to do so at the
time of grant. Amendments to the Plan shall be conditioned upon shareholder
approval only to the extent, if any, such approval is required by law (including
the Code and applicable NASDAQ or stock exchange requirements), as determined by
the Administrator. Notwithstanding the foregoing, the Company shall submit for
shareholder approval any amendment to the Plan (other than an amendment or
adjustment pursuant to Section 6) that would: (a) increase the maximum number of
shares for which options may be granted under the plan; (b) reduce the price at
which a Stock Option may be granted below the price provided for in Section
5(h); (c) reduce the exercise price of outstanding Stock Options; or (d)
increase the limits set forth in Section 3.

9.   OTHER COMPENSATION ARRANGEMENTS

          The existence of the Plan or the grant of any Stock Option will not in
any way affect the Company's right to award a person bonuses or other
compensation in addition to grants made under the Plan.

10.  DEFINITIONS

          The following terms, when used in the Plan, will have the meanings and
be subject to the provisions set forth below:

          "ADMINISTRATOR": has the meaning set forth in Section 2.

          "AFFILIATE": Any corporation or other entity owning, directly or
indirectly, 50% or more of the outstanding Stock of the Company, or in which the
Company or any such corporation or other entity owns, directly or indirectly,
50% of the outstanding capital stock (determined by aggregate voting rights) or
other voting interests.

          "BOARD": The Board of Directors of the Company.

          "CHANGE IN CONTROL": A change in ownership or control of the Company
or a change in the ownership of a substantial portion of the Company's assets,
determined in accordance with such rules, if any, as may be established by the
Administrator.

          "CODE": The U.S. Internal Revenue Code of 1986 as from time to time
amended and in effect, or any successor statute as from time to time in effect.

          "COMPENSATION COMMITTEE": The Compensation Committee of the Board.

          "COMPANY": Genzyme Corporation.

          "COVERED EMPLOYEES": A "covered employee" within the meaning of
Section 162(m).

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          "COVERED TRANSACTION": Any of (i) a consolidation, merger, or similar
transaction or series of related transactions in which the Company is not the
surviving corporation or which results in the acquisition of all or
substantially all of the Company's then outstanding common stock by a single
person or entity or by a group of persons and/or entities acting in concert,
(ii) a sale or transfer of all or substantially all the Company's assets, or
(iii) a dissolution or liquidation of the Company. Where a Covered Transaction
involves a tender offer that is reasonably expected to be followed by a merger
described in clause (i) (as determined by the Administrator), the Covered
Transaction shall be deemed to have occurred upon consummation of the tender
offer.

          "EMPLOYEE": Any person who is employed by the Company or an Affiliate.

          "EMPLOYMENT": A Participant's employment or other service relationship
with the Company and its Affiliates. Employment will be deemed to continue,
unless the Administrator expressly provides otherwise, so long as the
Participant is employed by, or otherwise is providing services in a capacity
described in Section 4 to the Company or its Affiliates. If a Participant's
employment or other service relationship is with an Affiliate and that entity
ceases to be an Affiliate, the Participant's Employment will be deemed to have
terminated when the entity ceases to be an Affiliate unless the Participant
transfers Employment to the Company or its remaining Affiliates.

          "EXCHANGE ACT": The Securities Exchange Act of 1934, as amended, as
from time to time further amended and in effect, or any successor statute as
from time to time in effect.

          "FAIR MARKET VALUE": The fair market value as determined by the
Compensation Committee in good faith, or in the manner established by the
Compensation Committee in good faith, from time to time.

          "ISO": A Stock Option intended to be an "incentive stock option"
within the meaning of Section 422 of the Code. Each option granted pursuant to
the Plan will be treated as providing by its terms that it is to be a
non-incentive option unless, as of the date of grant, it is expressly designated
as an ISO.

          "NSO": A Stock Option that is not an ISO.

          "PARTICIPANT": A person who is granted a Stock Option under the Plan.

          "PLAN": The Genzyme Corporation 2004 Equity Incentive Plan as from
time to time amended and in effect.

          "REPORTING PERSON": A person subject to the reporting requirements of
Section 16 of the Exchange Act.

          "SECTION 162(m)": Section 162(m) of the Code.

          "STOCK": Common Stock of the Company, par value $.01 per share.

          "STOCK OPTIONS": Options entitling the recipient to acquire shares of
Stock upon payment of the exercise price.