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                                                                    EXHIBIT 10.2

                              ALNYLAM HOLDING CO.

         2003 EMPLOYEE, DIRECTOR AND CONSULTANT STOCK PLAN, AS AMENDED



1.       DEFINITIONS.

         Unless otherwise specified or unless the context otherwise requires,
         the following terms, as used in this Alnylam Holding Co. 2003 Employee,
         Director and Consultant Stock Plan, have the following meanings:

                  Administrator means the Board of Directors, unless it has
                  delegated power to act on its behalf to the Committee, in
                  which case the Administrator means the Committee.

                  Affiliate means a corporation which, for purposes of Section
                  424 of the Code, is a parent or subsidiary of the Company,
                  direct or indirect.

                  Board of Directors means the Board of Directors of the
                  Company.

                  Change of Control means a merger or consolidation of the
                  Company whether or not approved by the Board of Directors,
                  other than a merger or consolidation which would result in the
                  voting securities of the Company outstanding immediately prior
                  thereto continuing to represent (either by remaining
                  outstanding or by being converted into voting securities of
                  the surviving entity or the parent of such corporation) at
                  least 50% of the total voting power represented by the voting
                  securities of the Company or such surviving entity or parent
                  of such corporation outstanding immediately after such merger
                  or consolidation, or the stockholders of the Company approve
                  an agreement for the sale or disposition by the Company of all
                  or substantially all of the Company's assets.

                  Code means the United States Internal Revenue Code of 1986, as
                  amended.

                  Committee means the committee of the Board of Directors to
                  which the Board of Directors has delegated power to act under
                  or pursuant to the provisions of the Plan.

                  Common Stock means shares of the Company's common stock,
                  $.0001 par value per share.

                  Company means Alnylam Holding Co., a Delaware corporation.

                  Disability or Disabled means permanent and total disability as
                  defined in Section 22(e)(3) of the Code.

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                  Employee means any employee of the Company or of an Affiliate
                  (including, without limitation, an employee who is also
                  serving as an officer or director of the Company or of an
                  Affiliate), designated by the Administrator to be eligible to
                  be granted one or more Stock Rights under the Plan.

                  Fair Market Value of a Share of Common Stock means:

                  (1) If the Common Stock is listed on a national securities
                  exchange or traded in the over-the-counter market and sales
                  prices are regularly reported for the Common Stock, the
                  closing or last price of the Common Stock on the Composite
                  Tape or other comparable reporting system for the trading day
                  immediately preceding the applicable date;

                  (2) If the Common Stock is not traded on a national securities
                  exchange but is traded on the over-the-counter market, if
                  sales prices are not regularly reported for the Common Stock
                  for the trading day referred to in clause (1), and if bid and
                  asked prices for the Common Stock are regularly reported, the
                  mean between the bid and the asked price for the Common Stock
                  at the close of trading in the over-the-counter market for the
                  trading day on which Common Stock was traded immediately
                  preceding the applicable date; and

                  (3) If the Common Stock is neither listed on a national
                  securities exchange nor traded in the over-the-counter market,
                  such value as the Administrator, in good faith, shall
                  determine.

                  ISO means an option meant to qualify as an incentive stock
                  option under Section 422 of the Code.

                  Non-Qualified Option means an option which is not intended to
                  qualify as an ISO.

                  Option means an ISO or Non-Qualified Option granted under the
                  Plan.

                  Option Agreement means an agreement between the Company and a
                  Participant delivered pursuant to the Plan, in such form as
                  the Administrator shall approve.

                  Participant means an Employee, director or consultant of the
                  Company or an Affiliate to whom one or more Stock Rights are
                  granted under the Plan. As used herein, "Participant" shall
                  include "Participant's Survivors" where the context requires.

                  Plan means this Alnylam Holding Co. 2003 Employee, Director
                  and Consultant Stock Plan.

                  Shares means shares of the Common Stock as to which Stock
                  Rights have been or may be granted under the Plan or any
                  shares of capital stock into which the Shares are changed or
                  for which they are exchanged within the provisions of
                  Paragraph 3

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                  of the Plan. The Shares issued under the Plan may be
                  authorized and unissued shares or shares held by the Company
                  in its treasury, or both.

                  Stock Grant means a grant by the Company of Shares under the
                  Plan.

                  Stock Grant Agreement means an agreement between the Company
                  and a Participant delivered pursuant to the Plan, in such form
                  as the Administrator shall approve.

                  Stock Right means a right to Shares of the Company granted
                  pursuant to the Plan -- an ISO, a Non-Qualified Option or a
                  Stock Grant.

                  Survivor means a deceased Participant's legal representatives
                  and/or any person or persons who acquired the Participant's
                  rights to a Stock Right by will or by the laws of descent and
                  distribution.

2.       PURPOSES OF THE PLAN.

         The Plan is intended to encourage ownership of Shares by Employees and
directors of and certain consultants to the Company in order to attract such
people, to induce them to work for the benefit of the Company or of an Affiliate
and to provide additional incentive for them to promote the success of the
Company or of an Affiliate. The Plan provides for the granting of ISOs,
Non-Qualified Options and Stock Grants.

3.       SHARES SUBJECT TO THE PLAN.

         (a)      The number of Shares which may be issued from time to time
pursuant to this Plan shall be (i) 944,812, plus (ii) such additional Shares
as are represented by options and other awards granted under the Company's 2002
Employee, Director and Consultant Stock Plan which are cancelled or expire
without delivery of shares of stock by the Company; provided, however, that the
number of Shares which may be issued from time to time pursuant to clause (ii)
shall not exceed 1,506,503, or the equivalent of such number of Shares after the
Administrator, in its sole discretion, has interpreted the effect of any stock
split, stock dividend, combination, recapitalization or similar transaction in
accordance with Paragraph 23 of the Plan.

         If an Option ceases to be "outstanding", in whole or in part, or if the
Company shall reacquire any Shares issued pursuant to a Stock Grant, the Shares
which were subject to such Option and any Shares so reacquired by the Company
shall be available for the granting of other Stock Rights under the Plan. Any
Option shall be treated as "outstanding" until such Option is exercised in full,
or terminates or expires under the provisions of the Plan, or by agreement of
the parties to the pertinent Option Agreement.

4.       ADMINISTRATION OF THE PLAN.

         The Administrator of the Plan will be the Board of Directors, except to
the extent the Board of Directors delegates its authority to the Committee, in
which case the Committee shall be the Administrator. Subject to the provisions
of the Plan, the Administrator is authorized to:

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         a.       Interpret the provisions of the Plan or of any Option or Stock
                  Grant and to make all rules and determinations which it deems
                  necessary or advisable for the administration of the Plan;

         b.       Determine which Employees, directors and consultants shall be
                  granted Stock Rights;

         c.       Determine the number of Shares for which a Stock Right or
                  Stock Rights shall be granted;

         d.       Specify the terms and conditions upon which a Stock Right or
                  Stock Rights may be granted; and

         e.       Adopt any sub-plans applicable to residents of any specified
                  jurisdiction as it deems necessary or appropriate in order to
                  comply with or take advantage of any tax laws applicable to
                  the Company or to Plan Participants or to otherwise facilitate
                  the administration of the Plan, which sub-plans may include
                  additional restrictions or conditions applicable to Options or
                  Shares acquired upon exercise of Options.

provided, however, that all such interpretations, rules, determinations, terms
and conditions shall be made and prescribed in the context of preserving the tax
status under Section 422 of the Code of those Options which are designated as
ISOs. Subject to the foregoing, the interpretation and construction by the
Administrator of any provisions of the Plan or of any Stock Right granted under
it shall be final, unless otherwise determined by the Board of Directors, if the
Administrator is the Committee. In addition, if the Administrator is the
Committee, the Board of Directors may take any action under the Plan that would
otherwise be the responsibility of the Committee.

         If permissible under applicable law, the Board of Directors or the
Committee may allocate all or any portion of its responsibilities and powers to
any one or more of its members and may delegate all or any portion of its
responsibilities and powers to any other person selected by it. Any such
allocation or delegation may be revoked by the Board of Directors or the
Committee at any time.

5.       ELIGIBILITY FOR PARTICIPATION.

         The Administrator will, in its sole discretion, name the Participants
in the Plan, provided, however, that each Participant must be an Employee,
director or consultant of the Company or of an Affiliate at the time a Stock
Right is granted. Notwithstanding the foregoing, the Administrator may authorize
the grant of a Stock Right to a person not then an Employee, director or
consultant of the Company or of an Affiliate; provided, however, that the actual
grant of such Stock Right shall be conditioned upon such person becoming
eligible to become a Participant at or prior to the time of the execution of the
Agreement evidencing such Stock Right. ISOs may be granted only to Employees.
Non-Qualified Options and Stock Grants may

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be granted to any Employee, director or consultant of the Company or an
Affiliate. The granting of any Stock Right to any individual shall neither
entitle that individual to, nor disqualify him or her from, participation in any
other grant of Stock Rights.

6.       TERMS AND CONDITIONS OF OPTIONS.

         Each Option shall be set forth in writing in an Option Agreement, duly
executed by the Company and, to the extent required by law or requested by the
Company, by the Participant. The Administrator may provide that Options be
granted subject to such terms and conditions, consistent with the terms and
conditions specifically required under this Plan, as the Administrator may deem
appropriate including, without limitation, subsequent approval by the
shareholders of the Company of this Plan or any amendments thereto. The Option
Agreements shall be subject to at least the following terms and conditions:

         A.       Non-Qualified Options: Each Option intended to be a
                  Non-Qualified Option shall be subject to the terms and
                  conditions which the Administrator determines to be
                  appropriate and in the best interest of the Company, subject
                  to the following minimum standards for any such Non-Qualified
                  Option:

                  a.       Option Price: Each Option Agreement shall state the
                           option price (per share) of the Shares covered by
                           each Option, which option price shall be determined
                           by the Administrator but shall not be less than the
                           par value per share of Common Stock.

                  b.       Each Option Agreement shall state the number of
                           Shares to which it pertains;

                  c.       Each Option Agreement shall state the date or dates
                           on which it first is exercisable and the date after
                           which it may no longer be exercised, and may provide
                           that the Option rights accrue or become exercisable
                           in installments over a period of months or years, or
                           upon the occurrence of certain conditions or the
                           attainment of stated goals or events; and

                  d.       Exercise of any Option may be conditioned upon the
                           Participant's execution of a Share purchase agreement
                           in form satisfactory to the Administrator providing
                           for certain protections for the Company and its other
                           shareholders, including requirements that:

                           i.       The Participant's or the Participant's
                                    Survivors' right to sell or transfer the
                                    Shares may be restricted; and

                           ii.      The Participant or the Participant's
                                    Survivors may be required to execute letters
                                    of investment intent and must also
                                    acknowledge that the Shares will bear
                                    legends noting any applicable restrictions.

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         B.       ISOs: Each Option intended to be an ISO shall be issued only
                  to an Employee and be subject to the following terms and
                  conditions, with such additional restrictions or changes as
                  the Administrator determines are appropriate but not in
                  conflict with Section 422 of the Code and relevant regulations
                  and rulings of the Internal Revenue Service:

                  a.       Minimum standards: The ISO shall meet the minimum
                           standards required of Non-Qualified Options, as
                           described in Paragraph 6(A) above, except clause (a)
                           thereunder.

                  b.       Option Price: Immediately before the ISO is granted,
                           if the Participant owns, directly or by reason of the
                           applicable attribution rules in Section 424(d) of the
                           Code:

                           i.       10% or less of the total combined voting
                                    power of all classes of stock of the Company
                                    or an Affiliate, the Option price per share
                                    of the Shares covered by each ISO shall not
                                    be less than 100% of the Fair Market Value
                                    per share of the Shares on the date of the
                                    grant of the Option; or

                           ii.      More than 10% of the total combined voting
                                    power of all classes of stock of the Company
                                    or an Affiliate, the Option price per share
                                    of the Shares covered by each ISO shall not
                                    be less than 110% of the said Fair Market
                                    Value on the date of grant.

                  c.       Term of Option: For Participants who own:

                           i.       10% or less of the total combined voting
                                    power of all classes of stock of the Company
                                    or an Affiliate, each ISO shall terminate
                                    not more than ten years from the date of the
                                    grant or at such earlier time as the Option
                                    Agreement may provide; or

                           ii.      More than 10% of the total combined voting
                                    power of all classes of stock of the Company
                                    or an Affiliate, each ISO shall terminate
                                    not more than five years from the date of
                                    the grant or at such earlier time as the
                                    Option Agreement may provide.

                  d.       Limitation on Yearly Exercise: The Option Agreements
                           shall restrict the amount of ISOs which may become
                           exercisable in any calendar year (under this or any
                           other ISO plan of the Company or an Affiliate) so
                           that the aggregate Fair Market Value (determined at
                           the time each ISO is granted) of the stock with
                           respect to which ISOs are exercisable for the first
                           time by the Participant in any calendar year does not
                           exceed $100,000.

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7.       TERMS AND CONDITIONS OF STOCK GRANTS.

         Each offer of a Stock Grant to a Participant shall state the date prior
to which the Stock Grant must be accepted by the Participant, and the principal
terms of each Stock Grant shall be set forth in a Stock Grant Agreement, duly
executed by the Company and, to the extent required by law or requested by the
Company, by the Participant. The Stock Grant Agreement shall be in a form
approved by the Administrator and shall contain terms and conditions which the
Administrator determines to be appropriate and in the best interest of the
Company, subject to the following minimum standards:

         (a)      Each Stock Grant Agreement shall state the purchase price (per
                  share), if any, of the Shares covered by each Stock Grant,
                  which purchase price shall be determined by the Administrator
                  but shall not be less than the minimum consideration required
                  by the Delaware General Corporation Law on the date of the
                  grant of the Stock Grant;

         (b)      Each Stock Grant Agreement shall state the number of Shares to
                  which the Stock Grant pertains; and

         (c)      Each Stock Grant Agreement shall include the terms of any
                  right of the Company to restrict or reacquire the Shares
                  subject to the Stock Grant, including the time and events upon
                  which such reacquisition rights shall accrue and the purchase
                  price therefor, if any.

8.       EXERCISE OF OPTIONS AND ISSUE OF SHARES.

         An Option (or any part or installment thereof) shall be exercised by
giving written notice to the Company or its designee, together with provision
for payment of the full purchase price in accordance with this Paragraph for the
Shares as to which the Option is being exercised, and upon compliance with any
other condition(s) set forth in the Option Agreement. Such notice shall be
signed by the person exercising the Option, shall state the number of Shares
with respect to which the Option is being exercised and shall contain any
representation required by the Plan or the Option Agreement. Payment of the
purchase price for the Shares as to which such Option is being exercised shall
be made (a) in United States dollars in cash or by check, or (b) at the
discretion of the Administrator, through delivery of shares of Common Stock
having a Fair Market Value equal as of the date of the exercise to the cash
exercise price of the Option and held for at least six months, or (c) at the
discretion of the Administrator, by delivery of the grantee's personal note, for
full, partial or no recourse, bearing interest payable not less than annually at
market rate on the date of exercise and at no less than 100% of the applicable
Federal rate, as defined in Section 1274(d) of the Code, with or without the
pledge of such Shares as collateral, or (d) at the discretion of the
Administrator, in accordance with a cashless exercise program established with a
securities brokerage firm, and approved by the Administrator, or (e) at the
discretion of the Administrator, by any combination of (a), (b), (c) and (d)
above. Notwithstanding the foregoing, the Administrator shall accept only such
payment on exercise of an ISO as is permitted by Section 422 of the Code.

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         The Company shall then reasonably promptly deliver the Shares as to
which such Option was exercised to the Participant (or to the Participant's
Survivors, as the case may be). In determining what constitutes "reasonably
promptly," it is expressly understood that the issuance and delivery of the
Shares may be delayed by the Company in order to comply with any law or
regulation (including, without limitation, state securities or "blue sky" laws)
which requires the Company to take any action with respect to the Shares prior
to their issuance. The Shares shall, upon delivery, be fully paid,
non-assessable Shares.

         The Administrator shall have the right to accelerate the date of
exercise of any installment of any Option; provided that the Administrator shall
not accelerate the exercise date of any installment of any Option granted to an
Employee as an ISO (and not previously converted into a Non-Qualified Option
pursuant to Paragraph 26) if such acceleration would violate the annual vesting
limitation contained in Section 422(d) of the Code, as described in Paragraph
6.B.d.

         The Administrator may, in its discretion, amend any term or condition
of an outstanding Option provided (i) such term or condition as amended is
permitted by the Plan, (ii) any such amendment shall be made only with the
consent of the Participant to whom the Option was granted, or in the event of
the death of the Participant, the Participant's Survivors, if the amendment is
adverse to the Participant, and (iii) any such amendment of any ISO shall be
made only after the Administrator determines whether such amendment would
constitute a "modification" of any Option which is an ISO (as that term is
defined in Section 424(h) of the Code) or would cause any adverse tax
consequences for the holder of such ISO.

9.       ACCEPTANCE OF STOCK GRANT AND ISSUE OF SHARES.

         A Stock Grant (or any part or installment thereof) shall be accepted by
executing the Stock Grant Agreement and delivering it to the Company or its
designee, together with provision for payment of the full purchase price, if
any, in accordance with this Paragraph for the Shares as to which such Stock
Grant is being accepted, and upon compliance with any other conditions set forth
in the Stock Grant Agreement. Payment of the purchase price for the Shares as to
which such Stock Grant is being accepted shall be made (a) in United States
dollars in cash or by check, or (b) at the discretion of the Administrator,
through delivery of shares of Common Stock held for at least six months and
having a Fair Market Value equal as of the date of acceptance of the Stock Grant
to the purchase price of the Stock Grant, or (c) at the discretion of the
Administrator, by delivery of the grantee's personal note, for full or partial
recourse as determined by the Administrator, bearing interest payable not less
than annually at no less than 100% of the applicable Federal rate, as defined in
Section 1274(d) of the Code, or (d) at the discretion of the Administrator, by
any combination of (a), (b) and (c) above.

         The Company shall then reasonably promptly deliver the Shares as to
which such Stock Grant was accepted to the Participant (or to the Participant's
Survivors, as the case may be), subject to any escrow provision set forth in the
Stock Grant Agreement. In determining what constitutes "reasonably promptly," it
is expressly understood that the issuance and delivery of the Shares may be
delayed by the Company in order to comply with any law or regulation

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(including, without limitation, state securities or "blue sky" laws) which
requires the Company to take any action with respect to the Shares prior to
their issuance.

         The Administrator may, in its discretion, amend any term or condition
of an outstanding Stock Grant or Stock Grant Agreement provided (i) such term or
condition as amended is permitted by the Plan, and (ii) any such amendment shall
be made only with the consent of the Participant to whom the Stock Grant was
made, if the amendment is adverse to the Participant.

10.      RIGHTS AS A SHAREHOLDER.

         No Participant to whom a Stock Right has been granted shall have rights
as a shareholder with respect to any Shares covered by such Stock Right, except
after due exercise of the Option or acceptance of the Stock Grant and tender of
the full purchase price, if any, for the Shares being purchased pursuant to such
exercise or acceptance and registration of the Shares in the Company's share
register in the name of the Participant.

11.      ASSIGNABILITY AND TRANSFERABILITY OF STOCK RIGHTS.

         By its terms, a Stock Right granted to a Participant shall not be
transferable by the Participant other than (i) by will or by the laws of descent
and distribution, or (ii) as approved by the Administrator in its discretion and
set forth in the applicable Option Agreement or Stock Grant Agreement.
Notwithstanding the foregoing, an ISO transferred except in compliance with
clause (i) above shall no longer qualify as an ISO. The designation of a
beneficiary of a Stock Right by a Participant, with the prior approval of the
Administrator and in such form as the Administrator shall prescribe, shall not
be deemed a transfer prohibited by this Paragraph. Except as provided above, a
Stock Right shall only be exercisable or may only be accepted, during the
Participant's lifetime, only by such Participant (or by his or her legal
representative) and shall not be assigned, pledged or hypothecated in any way
(whether by operation of law or otherwise) and shall not be subject to
execution, attachment or similar process. Any attempted transfer, assignment,
pledge, hypothecation or other disposition of any Stock Right or of any rights
granted thereunder contrary to the provisions of this Plan, or the levy of any
attachment or similar process upon a Stock Right, shall be null and void.

12.      EFFECT ON OPTIONS OF TERMINATION OF SERVICE OTHER THAN "FOR CAUSE" OR
         DEATH OR DISABILITY.

         Except as otherwise provided in a Participant's Option Agreement, in
the event of a termination of service (whether as an employee, director or
consultant) with the Company or an Affiliate before the Participant has
exercised an Option, the following rules apply:

         a.       A Participant who ceases to be an employee, director or
                  consultant of the Company or of an Affiliate (for any reason
                  other than termination "for cause", Disability, or death for
                  which events there are special rules in Paragraphs 13, 14,

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                  and 15, respectively), may exercise any Option granted to him
                  or her to the extent that the Option is exercisable on the
                  date of such termination of service, but only within such term
                  as the Administrator has designated in a Participant's Option
                  Agreement.

         b.       Except as provided in Subparagraph (c) below, or Paragraph 14
                  or 15, in no event may an Option intended to be an ISO, be
                  exercised later than three months after the Participant's
                  termination of employment.

         c.       The provisions of this Paragraph, and not the provisions of
                  Paragraph 14 or 15, shall apply to a Participant who
                  subsequently becomes Disabled or dies after the termination of
                  employment, director status or consultancy, provided, however,
                  in the case of a Participant's Disability or death within
                  three months after the termination of employment, director
                  status or consultancy, the Participant or the Participant's
                  Survivors may exercise the Option within one year after the
                  date of the Participant's termination of service, but in no
                  event after the date of expiration of the term of the Option.

         d.       Notwithstanding anything herein to the contrary, if subsequent
                  to a Participant's termination of employment, termination of
                  director status or termination of consultancy, but prior to
                  the exercise of an Option, the Board of Directors determines
                  that, either prior or subsequent to the Participant's
                  termination, the Participant engaged in conduct which would
                  constitute "cause", then such Participant shall forthwith
                  cease to have any right to exercise any Option.

         e.       A Participant to whom an Option has been granted under the
                  Plan who is absent from work with the Company or with an
                  Affiliate because of temporary disability (any disability
                  other than a permanent and total Disability as defined in
                  Paragraph 1 hereof), or who is on leave of absence for any
                  purpose, shall not, during the period of any such absence, be
                  deemed, by virtue of such absence alone, to have terminated
                  such Participant's employment, director status or consultancy
                  with the Company or with an Affiliate, except as the
                  Administrator may otherwise expressly provide.

         f.       Except as required by law or as set forth in a Participant's
                  Option Agreement, Options granted under the Plan shall not be
                  affected by any change of a Participant's status within or
                  among the Company and any Affiliates, so long as the
                  Participant continues to be an employee, director or
                  consultant of the Company or any Affiliate.

13.      EFFECT ON OPTIONS OF TERMINATION OF SERVICE "FOR CAUSE".

         Except as otherwise provided in a Participant's Option Agreement, the
following rules apply if the Participant's service (whether as an employee,
director or consultant) with the Company or an Affiliate is terminated "for
cause" prior to the time that all his or her outstanding Options have been
exercised:

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         a.       All outstanding and unexercised Options as of the time the
                  Participant is notified his or her service is terminated "for
                  cause" will immediately be forfeited.

         b.       For purposes of this Plan, "cause" shall include (and is not
                  limited to) dishonesty with respect to the Company or any
                  Affiliate, insubordination, substantial malfeasance or
                  non-feasance of duty, unauthorized disclosure of confidential
                  information, breach by the Participant of any provision of any
                  employment, consulting, advisory, nondisclosure,
                  non-competition or similar agreement between the Participant
                  and the Company, and conduct substantially prejudicial to the
                  business of the Company or any Affiliate. The determination of
                  the Administrator as to the existence of "cause" will be
                  conclusive on the Participant and the Company.

         c.       "Cause" is not limited to events which have occurred prior to
                  a Participant's termination of service, nor is it necessary
                  that the Administrator's finding of "cause" occur prior to
                  termination. If the Administrator determines, subsequent to a
                  Participant's termination of service but prior to the exercise
                  of an Option, that either prior or subsequent to the
                  Participant's termination the Participant engaged in conduct
                  which would constitute "cause", then the right to exercise any
                  Option is forfeited.

         d.       Any definition in an agreement between the Participant and the
                  Company or an Affiliate, which contains a conflicting
                  definition of "cause" for termination and which is in effect
                  at the time of such termination, shall supersede the
                  definition in this Plan with respect to that Participant.

14.      EFFECT ON OPTIONS OF TERMINATION OF SERVICE FOR DISABILITY.

         Except as otherwise provided in a Participant's Option Agreement, a
Participant who ceases to be an employee, director or consultant of the Company
or of an Affiliate by reason of Disability may exercise any Option granted to
such Participant:

         a.       To the extent that the Option has become exercisable but has
                  not been exercised on the date of Disability; and

         b.       In the event rights to exercise the Option accrue
                  periodically, to the extent of a pro rata portion through the
                  date of Disability of any additional vesting rights that would
                  have accrued on the next vesting date had the Participant not
                  become Disabled. The proration shall be based upon the number
                  of days accrued in the current vesting period prior to the
                  date of Disability.

         A Disabled Participant may exercise such rights only within the period
ending one year after the date of the Participant's termination of employment,
directorship or consultancy, as the case may be, notwithstanding that the
Participant might have been able to exercise the Option as

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to some or all of the Shares on a later date if the Participant had not become
Disabled and had continued to be an employee, director or consultant or, if
earlier, within the originally prescribed term of the Option.

         The Administrator shall make the determination both of whether
Disability has occurred and the date of its occurrence (unless a procedure for
such determination is set forth in another agreement between the Company and
such Participant, in which case such procedure shall be used for such
determination). If requested, the Participant shall be examined by a physician
selected or approved by the Administrator, the cost of which examination shall
be paid for by the Company.

15.      EFFECT ON OPTIONS OF DEATH WHILE AN EMPLOYEE, DIRECTOR OR CONSULTANT.

         Except as otherwise provided in a Participant's Option Agreement, in
the event of the death of a Participant while the Participant is an employee,
director or consultant of the Company or of an Affiliate, such Option may be
exercised by the Participant's Survivors:

         a.       To the extent that the Option has become exercisable but has
                  not been exercised on the date of death; and

         b.       In the event rights to exercise the Option accrue
                  periodically, to the extent of a pro rata portion through the
                  date of death of any additional vesting rights that would have
                  accrued on the next vesting date had the Participant not died.
                  The proration shall be based upon the number of days accrued
                  in the current vesting period prior to the Participant's date
                  of death.

         If the Participant's Survivors wish to exercise the Option, they must
take all necessary steps to exercise the Option within one year after the date
of death of such Participant, notwithstanding that the decedent might have been
able to exercise the Option as to some or all of the Shares on a later date if
he or she had not died and had continued to be an employee, director or
consultant or, if earlier, within the originally prescribed term of the Option.

16.      EFFECT OF TERMINATION OF SERVICE ON STOCK GRANTS.

         In the event of a termination of service (whether as an employee,
director or consultant) with the Company or an Affiliate for any reason before
the Participant has accepted a Stock Grant, such offer shall terminate.

         For purposes of this Paragraph 16 and Paragraph 17 below, a Participant
to whom a Stock Grant has been offered and accepted under the Plan who is absent
from work with the Company or with an Affiliate because of temporary disability
(any disability other than a permanent and total Disability as defined in
Paragraph 1 hereof), or who is on leave of absence for any purpose, shall not,
during the period of any such absence, be deemed, by virtue of such absence
alone, to

<PAGE>

have terminated such Participant's employment, director status or consultancy
with the Company or with an Affiliate, except as the Administrator may otherwise
expressly provide.

         In addition, for purposes of this Paragraph 16 and Paragraph 17 below,
any change of employment or other service within or among the Company and any
Affiliates shall not be treated as a termination of employment, director status
or consultancy so long as the Participant continues to be an employee, director
or consultant of the Company or any Affiliate.

17.      EFFECT ON STOCK GRANTS OF TERMINATION OF SERVICE OTHER THAN "FOR CAUSE"
         OR DEATH OR DISABILITY.

         Except as otherwise provided in a Participant's Stock Grant Agreement,
in the event of a termination of service (whether as an employee, director or
consultant), other than termination "for cause," Disability, or death for which
events there are special rules in Paragraphs 18, 19, and 20, respectively,
before all Company rights of repurchase shall have lapsed, then the Company
shall have the right to repurchase that number of Shares subject to a Stock
Grant as to which the Company's repurchase rights have not lapsed.

18.      EFFECT ON STOCK GRANTS OF TERMINATION OF SERVICE "FOR CAUSE".

         Except as otherwise provided in a Participant's Stock Grant Agreement,
the following rules apply if the Participant's service (whether as an employee,
director or consultant) with the Company or an Affiliate is terminated "for
cause":

         a.       All Shares subject to any Stock Grant shall be immediately
                  subject to repurchase by the Company at the purchase price, if
                  any, thereof.

         b.       For purposes of this Plan, "cause" shall include (and is not
                  limited to) dishonesty with respect to the employer,
                  insubordination, substantial malfeasance or non-feasance of
                  duty, unauthorized disclosure of confidential information,
                  breach by the Participant of any provision of any employment,
                  consulting, advisory, nondisclosure, non-competition or
                  similar agreement between the Participant and the Company, and
                  conduct substantially prejudicial to the business of the
                  Company or any Affiliate. The determination of the
                  Administrator as to the existence of "cause" will be
                  conclusive on the Participant and the Company.

         c.       "Cause" is not limited to events which have occurred prior to
                  a Participant's termination of service, nor is it necessary
                  that the Administrator's finding of "cause" occur prior to
                  termination. If the Administrator determines, subsequent to a
                  Participant's termination of service, that either prior or
                  subsequent to the Participant's termination the Participant
                  engaged in conduct which would constitute "cause," then the
                  Company's right to repurchase all of such Participant's Shares
                  shall apply.

<PAGE>

         d.       Any definition in an agreement between the Participant and the
                  Company or an Affiliate, which contains a conflicting
                  definition of "cause" for termination and which is in effect
                  at the time of such termination, shall supersede the
                  definition in this Plan with respect to that Participant.

19.      EFFECT ON STOCK GRANTS OF TERMINATION OF SERVICE FOR DISABILITY.

         Except as otherwise provided in a Participant's Stock Grant Agreement,
the following rules apply if a Participant ceases to be an employee, director or
consultant of the Company or of an Affiliate by reason of Disability: to the
extent the Company's rights of repurchase have not lapsed on the date of
Disability, they shall be exercisable; provided, however, that in the event such
rights of repurchase lapse periodically, such rights shall lapse to the extent
of a pro rata portion of the Shares subject to such Stock Grant through the date
of Disability as would have lapsed had the Participant not become Disabled. The
proration shall be based upon the number of days accrued prior to the date of
Disability.

         The Administrator shall make the determination both of whether
Disability has occurred and the date of its occurrence (unless a procedure for
such determination is set forth in another agreement between the Company and
such Participant, in which case such procedure shall be used for such
determination). If requested, the Participant shall be examined by a physician
selected or approved by the Administrator, the cost of which examination shall
be paid for by the Company.

20.      EFFECT ON STOCK GRANTS OF DEATH WHILE AN EMPLOYEE, DIRECTOR OR
         CONSULTANT.

         Except as otherwise provided in a Participant's Stock Grant Agreement,
the following rules apply in the event of the death of a Participant while the
Participant is an employee, director or consultant of the Company or of an
Affiliate: to the extent the Company's rights of repurchase have not lapsed on
the date of death, they shall be exercisable; provided, however, that in the
event such rights of repurchase lapse periodically, such rights shall lapse to
the extent of a pro rata portion of the Shares subject to such Stock Grant
through the date of death as would have lapsed had the Participant not died. The
proration shall be based upon the number of days accrued prior to the
Participant's death.

21.      PURCHASE FOR INVESTMENT.

         Unless the offering and sale of the Shares to be issued upon the
particular exercise or acceptance of a Stock Right shall have been effectively
registered under the Securities Act of 1933, as now in force or hereafter
amended (the "1933 Act"), the Company shall be under no obligation to issue the
Shares covered by such exercise unless and until the following conditions have
been fulfilled:

<PAGE>

         a.       The person(s) who exercise(s) or accept(s) such Stock Right
                  shall warrant to the Company, prior to the receipt of such
                  Shares, that such person(s) are acquiring such Shares for
                  their own respective accounts, for investment, and not with a
                  view to, or for sale in connection with, the distribution of
                  any such Shares, in which event the person(s) acquiring such
                  Shares shall be bound by the provisions of the following
                  legend which shall be endorsed upon the certificate(s)
                  evidencing their Shares issued pursuant to such exercise or
                  such grant:

                                    "The shares represented by this certificate
         have been taken for investment and they may not be sold or otherwise
         transferred by any person, including a pledgee, unless (1) either (a) a
         Registration Statement with respect to such shares shall be effective
         under the Securities Act of 1933, as amended, or (b) the Company shall
         have received an opinion of counsel satisfactory to it that an
         exemption from registration under such Act is then available, and (2)
         there shall have been compliance with all applicable state securities
         laws."

         b.       At the discretion of the Administrator, the Company shall have
                  received an opinion of its counsel that the Shares may be
                  issued upon such particular exercise or acceptance in
                  compliance with the 1933 Act without registration thereunder.

22.      DISSOLUTION OR LIQUIDATION OF THE COMPANY.

         Upon the dissolution or liquidation of the Company, all Options granted
under this Plan which as of such date shall not have been exercised and all
Stock Grants which have not been accepted will terminate and become null and
void; provided, however, that if the rights of a Participant or a Participant's
Survivors have not otherwise terminated and expired, the Participant or the
Participant's Survivors will have the right immediately prior to such
dissolution or liquidation to exercise or accept any Stock Right to the extent
that the Stock Right is exercisable or subject to acceptance as of the date
immediately prior to such dissolution or liquidation.

23.      ADJUSTMENTS.

         Upon the occurrence of any of the following events, a Participant's
rights with respect to any Stock Right granted to him or her hereunder shall be
adjusted as hereinafter provided, unless otherwise specifically provided in a
Participant's Option Agreement or Stock Grant Agreement:

         A.       Stock Dividends and Stock Splits. If (i) the shares of Common
Stock shall be subdivided or combined into a greater or smaller number of shares
or if the Company shall issue any shares of Common Stock as a stock dividend on
its outstanding Common Stock, or (ii) additional shares or new or different
shares or other securities of the Company or other non-

<PAGE>

cash assets are distributed with respect to such shares of Common Stock, the
number of shares of Common Stock deliverable upon the exercise or acceptance of
such Stock Right may be appropriately increased or decreased proportionately,
and appropriate adjustments may be made including, in the purchase price per
share, to reflect such events.

         B.       Corporate Transactions. If the Company is to be consolidated
with or acquired by another entity in a merger, sale of all or substantially all
of the Company's assets other than a transaction to merely change the state of
incorporation (a "Corporate Transaction"), the Administrator or the board of
directors of any entity assuming the obligations of the Company hereunder (the
"Successor Board"), shall, as to outstanding Options, either (i) make
appropriate provision for the continuation of such Options by substituting on an
equitable basis for the Shares then subject to such Options either the
consideration payable with respect to the outstanding shares of Common Stock in
connection with the Corporate Transaction or securities of any successor or
acquiring entity (provided, that, at the discretion of the Administrator, all
unvested Options shall be made fully or partially exercisable for purposes of
this Subparagraph upon the closing of the Corporate Transaction); or (ii) upon
written notice to the Participants, provide that all Options must be exercised
(either to the extent then exercisable or, at the discretion of the
Administrator, all Options being made fully or partially exercisable for
purposes of this Subparagraph), within a specified number of days of the date of
such notice, at the end of which period the Options shall terminate; or (iii)
terminate all Options in exchange for a cash payment equal to the excess of the
Fair Market Value of the Shares subject to such Options (either to the extent
then exercisable or, at the discretion of the Administrator, all Options being
made fully or partially exercisable for purposes of this Subparagraph) over the
exercise price thereof.

         With respect to outstanding Stock Grants, the Administrator or the
Successor Board, shall either (i) make appropriate provisions for the
continuation of such Stock Grants by substituting on an equitable basis for the
Shares then subject to such Stock Grants either the consideration payable with
respect to the outstanding Shares of Common Stock in connection with the
Corporate Transaction or securities of any successor or acquiring entity; or
(ii) upon written notice to the Participants, provide that all Stock Grants must
be accepted (to the extent then subject to acceptance) within a specified number
of days of the date of such notice, at the end of which period the offer of the
Stock Grants shall terminate; or (iii) terminate all Stock Grants in exchange
for a cash payment equal to the excess of the Fair Market Value of the Shares
subject to such Stock Grants over the purchase price thereof, if any. In
addition, in the event of a Corporate Transaction, the Administrator may waive
any or all Company repurchase rights with respect to outstanding Stock Grants.

         Notwithstanding the foregoing, individual Option Agreements and Stock
Grant Agreements may provide for different adjustments than those set forth
herein.

         C.       Recapitalization or Reorganization. In the event of a
recapitalization or reorganization of the Company other than a Corporate
Transaction pursuant to which securities of the Company or of another
corporation are issued with respect to the outstanding shares of Common Stock, a
Participant upon exercising or accepting a Stock Right after the
recapitalization or reorganization shall be entitled to receive for the purchase
price paid upon

<PAGE>

such exercise or acceptance the number of replacement securities which would
have been received if such Stock Right had been exercised or accepted prior to
such recapitalization or reorganization.

         D.       Modification of ISOs. Notwithstanding the foregoing, any
adjustments made pursuant to Subparagraph A, B or C above with respect to ISOs
shall be made only after the Administrator determines whether such adjustments
would constitute a "modification" of such ISOs (as that term is defined in
Section 424(h) of the Code) or would cause any adverse tax consequences for the
holders of such ISOs. If the Administrator determines that such adjustments made
with respect to ISOs would constitute a modification of such ISOs, it may
refrain from making such adjustments, unless the holder of an ISO specifically
requests in writing that such adjustment be made and such writing indicates that
the holder has full knowledge of the consequences of such "modification" on his
or her income tax treatment with respect to the ISO.

24.      ISSUANCES OF SECURITIES.

         Except as expressly provided herein, no issuance by the Company of
shares of stock of any class, or securities convertible into shares of stock of
any class, shall affect, and no adjustment by reason thereof shall be made with
respect to, the number or price of shares subject to Stock Rights. Except as
expressly provided herein, no adjustments shall be made for dividends paid in
cash or in property (including without limitation, securities) of the Company
prior to any issuance of Shares pursuant to a Stock Right.

25.      FRACTIONAL SHARES.

         No fractional shares shall be issued under the Plan and the person
exercising a Stock Right shall receive from the Company cash in lieu of such
fractional shares equal to the Fair Market Value thereof.

26.      CONVERSION OF ISOs INTO NON-QUALIFIED OPTIONS; TERMINATION OF ISOs.

         The Administrator, at the written request of any Participant, may in
its discretion take such actions as may be necessary to convert such
Participant's ISOs (or any portions thereof) that have not been exercised on the
date of conversion into Non-Qualified Options at any time prior to the
expiration of such ISOs, regardless of whether the Participant is an employee of
the Company or an Affiliate at the time of such conversion. At the time of such
conversion, the Administrator (with the consent of the Participant) may impose
such conditions on the exercise of the resulting Non-Qualified Options as the
Administrator in its discretion may determine, provided that such conditions
shall not be inconsistent with this Plan. Nothing in the Plan shall be deemed to
give any Participant the right to have such Participant's ISOs converted into
Non-Qualified Options, and no such conversion shall occur until and unless the
Administrator

<PAGE>

takes appropriate action. The Administrator, with the consent of the
Participant, may also terminate any portion of any ISO that has not been
exercised at the time of such conversion.

27.      WITHHOLDING.

         In the event that any federal, state, or local income taxes, employment
taxes, Federal Insurance Contributions Act ("F.I.C.A.") withholdings or other
amounts are required by applicable law or governmental regulation to be withheld
from the Participant's salary, wages or other remuneration in connection with
the exercise or acceptance of a Stock Right or in connection with a
Disqualifying Disposition (as defined in Paragraph 28) or upon the lapsing of
any right of repurchase, the Company may withhold from the Participant's
compensation, if any, or may require that the Participant advance in cash to the
Company, or to any Affiliate of the Company which employs or employed the
Participant, the statutory minimum amount of such withholdings unless a
different withholding arrangement, including the use of shares of the Company's
Common Stock or a promissory note, is authorized by the Administrator (and
permitted by law). For purposes hereof, the fair market value of the shares
withheld for purposes of payroll withholding shall be determined in the manner
provided in Paragraph 1 above, as of the most recent practicable date prior to
the date of exercise. If the fair market value of the shares withheld is less
than the amount of payroll withholdings required, the Participant may be
required to advance the difference in cash to the Company or the Affiliate
employer. The Administrator in its discretion may condition the exercise of an
Option for less than the then Fair Market Value on the Participant's payment of
such additional withholding.

28.      NOTICE TO COMPANY OF DISQUALIFYING DISPOSITION.

         Each Employee who receives an ISO must agree to notify the Company in
writing immediately after the Employee makes a Disqualifying Disposition of any
shares acquired pursuant to the exercise of an ISO. A Disqualifying Disposition
is defined in Section 424(c) of the Code and includes any disposition (including
any sale or gift) of such shares before the later of (a) two years after the
date the Employee was granted the ISO, or (b) one year after the date the
Employee acquired Shares by exercising the ISO, except as otherwise provided in
Section 424(c) of the Code. If the Employee has died before such stock is sold,
these holding period requirements do not apply and no Disqualifying Disposition
can occur thereafter.

29.      TERMINATION OF THE PLAN.

         The Plan will terminate on 10 years after adoption, the date which is
ten years from the earlier of the date of its adoption by the Board of Directors
and the date of its approval by the shareholders. The Plan may be terminated at
an earlier date by vote of the shareholders or the Board of Directors of the
Company; provided, however, that any such earlier termination shall not affect
any Option Agreements or Stock Grant Agreements executed prior to the effective
date of such termination.

<PAGE>

30.      AMENDMENT OF THE PLAN AND AGREEMENTS.

         The Plan may be amended by the shareholders of the Company. The Plan
may also be amended by the Administrator, including, without limitation, to the
extent necessary to qualify any or all outstanding Stock Rights granted under
the Plan or Stock Rights to be granted under the Plan for favorable federal
income tax treatment (including deferral of taxation upon exercise) as may be
afforded incentive stock options under Section 422 of the Code, and to the
extent necessary to qualify the shares issuable upon exercise or acceptance of
any outstanding Stock Rights granted, or Stock Rights to be granted, under the
Plan for listing on any national securities exchange or quotation in any
national automated quotation system of securities dealers. Any amendment
approved by the Administrator which the Administrator determines is of a scope
that requires shareholder approval shall be subject to obtaining such
shareholder approval. Any modification or amendment of the Plan shall not,
without the consent of a Participant, adversely affect his or her rights under a
Stock Right previously granted to him or her. With the consent of the
Participant affected, the Administrator may amend outstanding Option Agreements
and Stock Grant Agreements in a manner which may be adverse to the Participant
but which is not inconsistent with the Plan. In the discretion of the
Administrator, outstanding Option Agreements and Stock Grant Agreements may be
amended by the Administrator in a manner which is not adverse to the
Participant.

<PAGE>

31.      EMPLOYMENT OR OTHER RELATIONSHIP.

         Nothing in this Plan or any Option Agreement or Stock Grant Agreement
shall be deemed to prevent the Company or an Affiliate from terminating the
employment, consultancy or director status of a Participant, nor to prevent a
Participant from terminating his or her own employment, consultancy or director
status or to give any Participant a right to be retained in employment or other
service by the Company or any Affiliate for any period of time.

32.      GOVERNING LAW.

         This Plan shall be construed and enforced in accordance with the law of
the State of Delaware.


                                               As amended through April 26, 2004
<PAGE>

                        INCENTIVE STOCK OPTION AGREEMENT

                               ALNYLAM HOLDING CO.

      AGREEMENT made as of the ___ day of _______ 200_, between Alnylam Holding
Co. (the "Company"), a Delaware corporation having a principal place of business
in Cambridge, Massachusetts, and ____________ of ____________, an employee of an
Affiliate of the Company (the "Employee").

      WHEREAS, the Company desires to grant to the Employee an Option to
purchase shares of its common stock, $.0001 par value per share (the "Shares"),
under and for the purposes set forth in the Company's 2003 Employee, Director
and Consultant Stock Plan (the "Plan");

      WHEREAS, the Company and the Employee understand and agree that any terms
used and not defined herein have the same meanings as in the Plan; and

      WHEREAS, the Company and the Employee each intend that the Option granted
herein qualify as an ISO.

      NOW, THEREFORE, in consideration of the mutual covenants hereinafter set
forth and for other good and valuable consideration, the parties hereto agree as
follows:

      1.    GRANT OF OPTION.

      The Company hereby grants to the Employee the right and option to purchase
all or any part of an aggregate of ________________ Shares (the "Total Shares"),
on the terms and conditions and subject to all the limitations set forth herein,
under United States securities and tax laws, and in the Plan, which is
incorporated herein by reference. The Employee acknowledges receipt of a copy of
the Plan.

      2.    PURCHASE PRICE.

      The purchase price of the Shares covered by the Option shall be $____ per
Share, subject to adjustment, as provided in the Plan, in the event of a stock
split, reverse stock split or other events affecting the holders of Shares after
the date hereof (the "Purchase Price"). Payment shall be made in accordance with
Paragraph 8 of the Plan.

      3.    EXERCISABILITY OF OPTION.

      Subject to the terms and conditions set forth in this Agreement and the
Plan, the Option granted hereby shall become exercisable for up to  _________ of
the Shares on the last day of _________ (the "First Anniversary Date")and for an
additional _________ of the Shares on the last day of each _____, _____, _____
and _____

<PAGE>
 of each year after the first anniversary of this Agreement until 100% of the
Shares have become vested.

      Alternatively, at the election of the Employee, the Option may be
exercised in whole or in part at any time as to Shares which have not yet vested
in accordance with the above schedule; provided however, as a condition to
exercising the Option for such unvested Shares, the Employee shall execute a
Restricted Stock Agreement in the form attached hereto as Exhibit C.

      The foregoing rights are cumulative and are subject to the other terms and
conditions of this Agreement and the Plan.

      4.    TERM OF OPTION.

      The Option shall terminate ten years from the date of this Agreement or,
if the Employee owns as of the date hereof more than 10% of the total combined
voting power of all classes of capital stock of the Company or an Affiliate,
five years from the date of this Agreement, but shall be subject to earlier
termination as provided herein or in the Plan.

      If the Employee ceases to be an employee of the Company or of an Affiliate
(for any reason other than the death or Disability of the Employee or
termination of the Employee's employment for "cause" (as defined in the Plan),
the Option may be exercised, if it has not previously terminated, within three
months after the date the Employee ceases to be an employee of the Company or an
Affiliate, or within the originally prescribed term of the Option, whichever is
earlier, but may not be exercised thereafter. In such event, the Option shall be
exercisable only to the extent that the Option has become exercisable and is in
effect at the date of such cessation of employment.

      Notwithstanding the foregoing, in the event of the Employee's Disability
or death within three months after the termination of employment, the Employee
or the Employee's Survivors may exercise the Option within one year after the
date of the Employee's termination of employment, but in no event after the date
of expiration of the term of the Option.

      In the event the Employee's employment is terminated by the Employee's
employer for "cause" (as defined in the Plan), the Employee's right to exercise
any unexercised portion of this Option shall cease immediately as of the time
the Employee is notified his or her employment is terminated for "cause," and
this Option shall thereupon terminate. Notwithstanding anything herein to the
contrary, if subsequent to the Employee's termination as an employee, but prior
to the exercise of the Option, the Board of Directors of the Company determines
that, either prior or subsequent to the Employee's termination, the Employee
engaged in conduct which would constitute "cause," then the Employee shall
immediately cease to have any right to exercise the Option and this Option shall
thereupon terminate.

      In the event of the Disability of the Employee, as determined in
accordance with the Plan, the Option shall be exercisable within one year after
the Employee's termination of employment or, if earlier, within the term
originally prescribed by the Option. In such event, the Option shall be
exercisable:

                                       2

<PAGE>

      (a)   to the extent that the Option has become exercisable but has not
            been exercised as of the date of Disability; and

      (b)   in the event rights to exercise the Option accrue periodically, to
            the extent of a pro rata portion through the date of Disability of
            any additional vesting rights that would have accrued on the next
            vesting date had the Employee not become Disabled. The proration
            shall be based upon the number of days accrued in the current
            vesting period prior to the date of Disability.

      In the event of the death of the Employee while an employee of the Company
or of an Affiliate, the Option shall be exercisable by the Employee's Survivors
within one year after the date of death of the Employee or, if earlier, within
the originally prescribed term of the Option. In such event, the Option shall be
exercisable:

      (x)   to the extent that the Option has become exercisable but has not
            been exercised as of the date of death; and

      (y)   in the event rights to exercise the Option accrue periodically, to
            the extent of a pro rata portion through the date of death of any
            additional vesting rights that would have accrued on the next
            vesting date had the Employee not died. The proration shall be based
            upon the number of days accrued in the current vesting period prior
            to the Employee's date of death.

      5.    METHOD OF EXERCISING OPTION.

      Subject to the terms and conditions of this Agreement, the Option may be
exercised by written notice to the Company or its designee, in substantially the
form of Exhibit A attached hereto. Such notice shall state the number of Shares
with respect to which the Option is being exercised and shall be signed by the
person exercising the Option. Payment of the purchase price for such Shares
shall be made in accordance with Paragraph 8 of the Plan. The Company shall
deliver a certificate or certificates representing such Shares as soon as
practicable after the notice shall be received, provided, however, that the
Company may delay issuance of such Shares until completion of any action or
obtaining of any consent, which the Company deems necessary under any applicable
law (including, without limitation, state securities or "blue sky" laws). The
certificate or certificates for the Shares as to which the Option shall have
been so exercised shall be registered in the Company's share register in the
name of the person so exercising the Option (or, if the Option shall be
exercised by the Employee and if the Employee shall so request in the notice
exercising the Option, shall be registered in the name of the Employee and
another person jointly, with right of survivorship) and shall be delivered as
provided above to or upon the written order of the person exercising the Option.
In the event the Option shall be exercised, pursuant to Section 4 hereof, by any
person other than the Employee, such notice shall be accompanied by appropriate
proof of the right of such person to exercise the Option. All Shares that shall
be purchased upon the exercise of the Option as provided herein shall be fully
paid and nonassessable.

                                       3

<PAGE>

      6.    PARTIAL EXERCISE.

      Exercise of this Option to the extent above stated may be made in part at
any time and from time to time within the above limits, except that no
fractional share shall be issued pursuant to this Option.

      7.    NON-ASSIGNABILITY.

      The Option shall not be transferable by the Employee otherwise than by
will or by the laws of descent and distribution. The Option shall be
exercisable, during the Employee's lifetime, only by the Employee (or, in the
event of legal incapacity or incompetency, by the Employee's guardian or
representative) and shall not be assigned, pledged or hypothecated in any way
(whether by operation of law or otherwise) and shall not be subject to
execution, attachment or similar process. Any attempted transfer, assignment,
pledge, hypothecation or other disposition of the Option or of any rights
granted hereunder contrary to the provisions of this Section 7, or the levy of
any attachment or similar process upon the Option shall be null and void.

      8.    NO RIGHTS AS STOCKHOLDER UNTIL EXERCISE.

      The Employee shall have no rights as a stockholder with respect to Shares
subject to this Agreement until registration of the Shares in the Company's
share register in the name of the Employee. Except as is expressly provided in
the Plan with respect to certain changes in the capitalization of the Company,
no adjustment shall be made for dividends or similar rights for which the record
date is prior to the date of such registration.

      9.    ADJUSTMENTS.

      The Plan contains provisions covering the treatment of Options in a number
of contingencies such as stock splits and mergers. Provisions in the Plan for
adjustment with respect to stock subject to Options and the related provisions
with respect to successors to the business of the Company are hereby made
applicable hereunder and are incorporated herein by reference, provided,
however, in the event of a Change of Control (as defined in the Plan) which the
Administrator (as defined in the Plan) or the Successor Board (as defined in the
Plan) makes provisions for the treatment of Options under (A) clause (i) of the
first paragraph of Section 23(B) of the Plan, an additional one-sixteenth (1/16)
of the Shares shall become fully vested and immediately exercisable immediately
prior to such Change of Control and the remaining Shares which have not vested
shall vest in accordance with Section 3 above, provided, however, if the
Employee's employment with the Company is Terminated (as defined below), fifty
percent (50%) of the Shares which have not yet vested in accordance with Section
3 above shall become fully vested and immediately exercisable immediately prior
to such termination (for purposes of this Section 9, the Employee shall be
deemed to have been "Terminated" if at any time before the six-month anniversary
of the closing of such Change of Control, (i) the Employee shall fail to be
vested with power and authority analogous to the Employee's title and/or office
prior to such Change of Control, (ii) the Employee shall lose any significant
duties or responsibilities attending such office, (iii) there shall occur a
reduction in the Employee's base compensation, or

                                       4
<PAGE>

(iv) the Employee's employment with the Company or an Affiliate, or its
successor, is terminated without "cause" (as defined in the Plan)) or (B) either
clause (ii) or (iii) of the first paragraph of Section 23(B) of the Plan, all
Shares under this Option shall become fully vested and immediately exercisable
prior to such Change of Control.

      10.   TAXES.

      The Employee acknowledges that any income or other taxes due from him or
her with respect to this Option or the Shares issuable pursuant to this Option
shall be the Employee's responsibility.

      In the event of a Disqualifying Disposition (as defined in Section 15
below) or if the Option is converted into a Non-Qualified Option and such
Non-Qualified Option is exercised, the Company may withhold from the Employee's
remuneration, if any, the minimum statutory amount of federal, state and local
withholding taxes attributable to such amount that is considered compensation
includable in such person's gross income. At the Company's discretion, the
amount required to be withheld may be withheld in cash from such remuneration,
or in kind from the Shares otherwise deliverable to the Employee on exercise of
the Option. The Employee further agrees that, if the Company does not withhold
an amount from the Employee's remuneration sufficient to satisfy the Company's
income tax withholding obligation, the Employee will reimburse the Company on
demand, in cash, for the amount under-withheld.

      11.   PURCHASE FOR INVESTMENT.

      Unless the offering and sale of the Shares to be issued upon the
particular exercise of the Option shall have been effectively registered under
the Securities Act of 1933, as now in force or hereafter amended (the "1933
Act"), the Company shall be under no obligation to issue the Shares covered by
such exercise unless and until the following conditions have been fulfilled:

      (a)   The person(s) who exercise the Option shall warrant to the Company,
            at the time of such exercise, that such person(s) are acquiring such
            Shares for their own respective accounts, for investment, and not
            with a view to, or for sale in connection with, the distribution of
            any such Shares, in which event the person(s) acquiring such Shares
            shall be bound by the provisions of the following legend which shall
            be endorsed upon the certificate(s) evidencing the Shares issued
            pursuant to such exercise:

                  "The shares represented by this certificate have been taken
                  for investment and they may not be sold or otherwise
                  transferred by any person, including a pledgee, unless (1)
                  either (a) a Registration Statement with respect to such
                  shares shall be effective under the Securities Act of 1933, as
                  amended, or (b) the Company shall have received an opinion of
                  counsel satisfactory to it that an exemption from registration
                  under such Act is then available, and (2) there shall have
                  been compliance with all applicable state securities laws;"
                  and

                                       5
<PAGE>

      (b)   If the Company so requires, the Company shall have received an
            opinion of its counsel that the Shares may be issued upon such
            particular exercise in compliance with the 1933 Act without
            registration thereunder. Without limiting the generality of the
            foregoing, the Company may delay issuance of the Shares until
            completion of any action or obtaining of any consent, which the
            Company deems necessary under any applicable law (including without
            limitation state securities or "blue sky" laws).

      12.   RESTRICTIONS ON TRANSFER OF SHARES.

      12.1  The Shares acquired by the Employee pursuant to the exercise of the
Option granted hereby shall not be transferred by the Employee except as
permitted herein.

      12.2  In the event of the Employee's termination of employment for any
reason, the Company shall have the option, but not the obligation, to repurchase
all or any part of the Shares issued pursuant to this Agreement (including,
without limitation, Shares purchased after termination of employment, Disability
or death in accordance with Section 4 hereof). In the event the Company does
not, upon the termination of employment of the Employee (as described above),
exercise its option pursuant to this Section 12.2, the restrictions set forth in
the balance of this Agreement shall not thereby lapse, and the Employee for
himself or herself, his or her heirs, legatees, executors, administrators and
other successors in interest, agrees that the Shares shall remain subject to
such restrictions. The following provisions shall apply to a repurchase under
this Section 12.2:

      (i)   The per share repurchase price of the Shares to be sold to the
            Company upon exercise of its option under this Section 12.2 shall be
            equal to the Fair Market Value of each such Share determined in
            accordance with the Plan as of the date of termination of employment
            provided, however, in the event of a termination by the Company for
            "cause" (as defined in the Plan), the per share repurchase price of
            the Shares to be sold to the Company upon exercise of its option
            under this Section 12.2 shall be equal to the Purchase Price.

      (ii)  The Company's option to repurchase the Employee's Shares in the
            event of termination of employment shall be valid for a period of 12
            months commencing with the date of such termination of employment.

      (iii) In the event the Company shall be entitled to and shall elect to
            exercise its option to repurchase the Employee's Shares under this
            Section 12.2, the Company shall notify the Employee, or in case of
            death, his or her Survivor, in writing of its intent to repurchase
            the Shares. Such written notice may be mailed by the Company up to
            and including the last day of the time period provided for in
            Section 12.2(ii) for exercise of the Company's option to repurchase.

      (iv)  The written notice to the Employee shall specify the address at, and
            the time and date on, which payment of the repurchase price is to be
            made (the "Closing"). The date specified shall not be less than ten
            days nor more than 60 days from the

                                       6
<PAGE>

            date of the mailing of the notice, and the Employee or his or her
            successor in interest with respect to the Shares shall have no
            further rights as the owner thereof from and after the date
            specified in the notice. At the Closing, the repurchase price shall
            be delivered to the Employee or his or her successor in interest and
            the Shares being purchased, duly endorsed for transfer, shall, to
            the extent that they are not then in the possession of the Company,
            be delivered to the Company by the Employee or his or her successor
            in interest.

      12.3  It shall be a condition precedent to the validity of any sale or
other transfer of any Shares by the Employee that the following restrictions be
complied with (except as hereinafter otherwise provided):

      (i)   No Shares owned by the Employee may be sold, pledged or otherwise
            transferred (including by gift or devise) to any person or entity,
            voluntarily, or by operation of law, except in accordance with the
            terms and conditions hereinafter set forth.

      (ii)  Before selling or otherwise transferring all or part of the Shares,
            the Employee shall give written notice of such intention to the
            Company, which notice shall include the name of the proposed
            transferee, the proposed purchase price per share, the terms of
            payment of such purchase price and all other matters relating to
            such sale or transfer and shall be accompanied by a copy of the
            binding written agreement of the proposed transferee to purchase the
            Shares of the Employee. Such notice shall constitute a binding offer
            by the Employee to sell to the Company such number of the Shares
            then held by the Employee as are proposed to be sold in the notice
            at the monetary price per share designated in such notice, payable
            on the terms offered to the Employee by the proposed transferee
            (provided, however, that the Company shall not be required to meet
            any non-monetary terms of the proposed transfer, including, without
            limitation, delivery of other securities in exchange for the Shares
            proposed to be sold). The Company shall give written notice to the
            Employee as to whether such offer has been accepted in whole by the
            Company within 60 days after its receipt of written notice from the
            Employee. The Company may only accept such offer in whole and may
            not accept such offer in part. Such acceptance notice shall fix a
            time, location and date for the closing on such purchase ("Closing
            Date") which shall not be less than ten nor more than 60 days after
            the giving of the acceptance notice. The place for such closing
            shall be at the Company's principal office. At such closing, the
            Employee shall accept payment as set forth herein and shall deliver
            to the Company in exchange therefor certificates for the number of
            Shares stated in the notice accompanied by duly executed instruments
            of transfer.

      (iii) If the Company shall fail to accept any such offer, the Employee
            shall be free to sell all, but not less than all, of the Shares set
            forth in his or her notice to the designated transferee at the price
            and terms designated in the Employee's notice, provided that (i)
            such sale is consummated within six months after the giving of
            notice by the Employee to the Company as aforesaid, and (ii) the
            transferee first agrees in writing to be bound by the provisions of
            this Section 12 so that such

                                       7
<PAGE>

            transferee (and all subsequent transferees) shall thereafter only be
            permitted to sell or transfer the Shares in accordance with the
            terms hereof. After the expiration of such six months, the
            provisions of this Section 12.3 shall again apply with respect to
            any proposed voluntary transfer of the Employee's Shares.

      (iv)  The restrictions on transfer contained in this Section 12.3 shall
            not apply to (a) transfers by the Employee to his or her spouse or
            children or to a trust for the benefit of his or her spouse or
            children, (b) transfers by the Employee to his or her guardian or
            conservator, and (c) or transfers by the Employee, in the event of
            his or her death, to his or her executor(s) or administrator(s) or
            to trustee(s) under his or her will (collectively, "Permitted
            Transferees"); provided however, that in any such event the Shares
            so transferred in the hands of each such Permitted Transferee shall
            remain subject to this Agreement, and each such Permitted Transferee
            shall so acknowledge in writing as a condition precedent to the
            effectiveness of such transfer.

      (v)   The provisions of this Section 12.3 may be waived by the Company.
            Any such waiver may be unconditional or based upon such conditions
            as the Company may impose.

      12.4  In the event that the Employee or his or her successor in interest
fails to deliver the Shares to be repurchased by the Company under this
Agreement, the Company may elect (a) to establish a segregated account in the
amount of the repurchase price, such account to be turned over to the Employee
or his or her successor in interest upon delivery of such Shares, and (b)
immediately to take such action as is appropriate to transfer record title of
such Shares from the Employee to the Company and to treat the Employee and such
Shares in all respects as if delivery of such Shares had been made as required
by this Agreement. The Employee hereby irrevocably grants the Company a power of
attorney which shall be coupled with an interest for the purpose of effectuating
the preceding sentence.

      12.5  If the Company shall pay a stock dividend or declare a stock split
on or with respect to any of its Common Stock, or otherwise distribute
securities of the Company to the holders of its Common Stock, the number of
shares of stock or other securities of Company issued with respect to the shares
then subject to the restrictions contained in this Agreement shall be added to
the Shares subject to the Company's rights to repurchase pursuant to this
Agreement. If the Company shall distribute to its stockholders shares of stock
of another corporation, the shares of stock of such other corporation,
distributed with respect to the Shares then subject to the restrictions
contained in this Agreement, shall be added to the Shares subject to the
Company's rights to repurchase pursuant to this Agreement.

      12.6  If the outstanding shares of Common Stock of the Company shall be
subdivided into a greater number of shares or combined into a smaller number of
shares, or in the event of a reclassification of the outstanding shares of
Common Stock of the Company, or if the Company shall be a party to a merger,
consolidation or capital reorganization, there shall be substituted for the
Shares then subject to the restrictions contained in this Agreement such amount
and kind of securities as are issued in such subdivision, combination,
reclassification, merger, consolidation

                                       8
<PAGE>

or capital reorganization in respect of the Shares subject immediately prior
thereto to the Company's rights to repurchase pursuant to this Agreement.

      12.7  The Company shall not be required to transfer any Shares on its
books which shall have been sold, assigned or otherwise transferred in violation
of this Agreement, or to treat as owner of such Shares, or to accord the right
to vote as such owner or to pay dividends to, any person or organization to
which any such Shares shall have been so sold, assigned or otherwise
transferred, in violation of this Agreement.

      12.8  The provisions of Sections 12.1, 12.2 and 12.3 shall terminate upon
the consummation of a public offering of any of the Company's securities
pursuant to a registration statement filed with the Securities and Exchange
Commission pursuant to the 1933 Act.

      12.9  If, in connection with a registration statement filed by the Company
pursuant to the 1933 Act, the Company or its underwriter so requests, the
Employee will agree not to sell any Shares for a period not to exceed 180 days
following the effectiveness of such registration.

      12.10 The Employee acknowledges and agrees that neither the Company, its
shareholders nor its directors and officers, has any duty or obligation to
disclose to the Employee any material information regarding the business of the
Company or affecting the value of the Shares before, at the time of, or
following a termination of the employment of the Employee by the Company, or an
Affiliate, including, without limitation, any information concerning plans for
the Company to make a public offering of its securities or to be acquired by or
merged with or into another firm or entity.

      12.11 All certificates representing the Shares to be issued to the
Employee pursuant to this Agreement shall have endorsed thereon a legend
substantially as follows: "The shares represented by this certificate are
subject to restrictions set forth in an Incentive Stock Option Agreement dated
_________, 200__ with this Company, a copy of which Agreement is available for
inspection at the offices of the Company or will be made available upon
request."

      13.   NO OBLIGATION TO EMPLOY.

      The Company is not by the Plan or this Option obligated to continue the
Employee as an employee of the Company or an Affiliate. The Employee
acknowledges: (i) that the Plan is discretionary in nature and may be suspended
or terminated by the Company at any time; (ii) that the grant of the Option is a
one-time benefit which does not create any contractual or other right to receive
future grants of options, or benefits in lieu of options; (iii) that all
determinations with respect to any such future grants, including, but not
limited to, the times when options shall be granted, the number of shares
subject to each option, the option price, and the time or times when each option
shall be exercisable, will be at the sole discretion of the Company; (iv) that
the Employee's participation in the Plan is voluntary; (v) that the value of the
Option is an extraordinary item of compensation which is outside the scope of
the Employee's employment contract, if any; and (vi) that the Option is not part
of normal or expected compensation for purposes of calculating any severance,
resignation, redundancy, end of service payments, bonuses, long-service awards,
pension or retirement benefits or similar payments.

                                       9
<PAGE>

      14.   OPTION IS INTENDED TO BE AN ISO.

      The parties each intend that the Option be an ISO so that the Employee (or
the Employee's Survivors) may qualify for the favorable tax treatment provided
to holders of Options that meet the standards of Section 422 of the Code. Any
provision of this Agreement or the Plan which conflicts with the Code so that
this Option would not be deemed an ISO is null and void and any ambiguities
shall be resolved so that the Option qualifies as an ISO. Nonetheless, if the
Option is determined not to be an ISO, the Employee understands that neither the
Company nor any Affiliate is responsible to compensate him or her or otherwise
make up for the treatment of the Option as a Non-qualified Option and not as an
ISO. The Employee should consult with the Employee's own tax advisors regarding
the tax effects of the Option and the requirements necessary to obtain favorable
tax treatment under Section 422 of the Code, including, but not limited to,
holding period requirements.

      15.   NOTICE TO COMPANY OF DISQUALIFYING DISPOSITION.

      The Employee agrees to notify the Company in writing immediately after the
Employee makes a Disqualifying Disposition of any of the Shares acquired
pursuant to the exercise of the Option. A Disqualifying Disposition is defined
in Section 424(c) of the Code and includes any disposition (including any sale)
of such Shares before the later of (a) two years after the date the Employee was
granted the Option or (b) one year after the date the Employee acquired Shares
by exercising the Option, except as otherwise provided in Section 424(c) of the
Code. If the Employee has died before the Shares are sold, these holding period
requirements do not apply and no Disqualifying Disposition can occur thereafter.

      16.   NOTICES.

      Any notices required or permitted by the terms of this Agreement or the
Plan shall be given by recognized courier service, facsimile, registered or
certified mail, return receipt requested, addressed as follows:

If to the Company:

                              Alnylam Holding Co.

                             _____________________________________

                             _____________________________________

If to the Employee:
                             _____________________________________

                             _____________________________________

                             _____________________________________

or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given upon
the earlier of receipt, one

                                       10
<PAGE>

business day following delivery to a recognized courier service or three
business days following mailing by registered or certified mail.

      17.   GOVERNING LAW.

      This Agreement shall be construed and enforced in accordance with the law
of the State of Delaware, without giving effect to the conflict of law
principles thereof. . For the purpose of litigating any dispute that arises
under this Agreement, the parties hereby consent to exclusive jurisdiction in
Massachusetts and agree that such litigation shall be conducted in the courts of
Suffolk County, Massachusetts or the federal courts of the United States for the
District of Massachusetts.

                                       11
<PAGE>

      18.   BENEFIT OF AGREEMENT.

      Subject to the provisions of the Plan and the other provisions hereof,
this Agreement shall be for the benefit of and shall be binding upon the heirs,
executors, administrators, successors and assigns of the parties hereto.

      19.   ENTIRE AGREEMENT.

      This Agreement, together with the Plan, embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior oral or written agreements and understandings
relating to the subject matter hereof. No statement, representation, warranty,
covenant or agreement not expressly set forth in this Agreement shall affect or
be used to interpret, change or restrict, the express terms and provisions of
this Agreement, provided, however, in any event, this Agreement shall be subject
to and governed by the Plan.

      20.   MODIFICATIONS AND AMENDMENTS.

      The terms and provisions of this Agreement may be modified or amended as
provided in the Plan.

      21.   WAIVERS AND CONSENTS.

      Except as provided in the Plan, the terms and provisions of this Agreement
may be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be
effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

      22.   DATA PRIVACY.

      By entering into this Agreement, the Employee: (i) authorizes the Company
and each Affiliate, and any agent of the Company or any Affiliate administering
the Plan or providing Plan recordkeeping services, to disclose to the Company or
any of its Affiliates such information and data as the Company or any such
Affiliate shall request in order to facilitate the grant of options and the
administration of the Plan; (ii) waives any data privacy rights he or she may
have with respect to such information; and (iii) authorizes the Company and each
Affiliate to store and transmit such information in electronic form.

                                       12
<PAGE>

      23.   CONSENT OF SPOUSE.

      If the Employee is married as of the date of this Agreement, the
Employee's spouse shall execute a Consent of Spouse in the form of Exhibit B
hereto, effective as of the date hereof. Such consent shall not be deemed to
confer or convey to the spouse any rights in the Shares that do not otherwise
exist by operation of law or the agreement of the parties. If the Employee
marries or remarries subsequent to the date hereof, the Employee shall, not
later than 60 days thereafter, obtain his or her new spouse's acknowledgement of
and consent to the existence and binding effect of Section 12.2 of this
Agreement by such spouse's executing and delivering a Consent of Spouse in the
form of Exhibit B.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       13
<PAGE>

      IN WITNESS WHEREOF, the Company has caused this Agreement to be executed
by its duly authorized officer, and the Employee has hereunto set his or her
hand, all as of the day and year first above written.

                               ALNYLAM HOLDING CO.

                               By:_____________________________________________
                                  Name
                                  Title
                               ________________________________________________
                               Employee

                                       14
<PAGE>

                                                                       Exhibit A

                  NOTICE OF EXERCISE OF INCENTIVE STOCK OPTION

                         [FORM FOR UNREGISTERED SHARES]

To:   Alnylam Holding Co.
      __________________________
      __________________________

Ladies and Gentlemen:

      I hereby exercise my Incentive Stock Option to purchase ___________ shares
(the "Shares") of the common stock, $.0001 par value, of Alnylam Holding Co.
(the "Company"), at the exercise price of $____ per share, pursuant to and
subject to the terms of that certain Incentive Stock Option Agreement between
the undersigned and the Company dated _________, 200_.

      I am aware that the Shares have not been registered under the Securities
Act of 1933, as amended (the "1933 Act"), or any state securities laws. I
understand that the reliance by the Company on exemptions under the 1933 Act is
predicated in part upon the truth and accuracy of the statements by me in this
Notice of Exercise.

      I hereby represent and warrant that (1) I have been furnished with all
information which I deem necessary to evaluate the merits and risks of the
purchase of the Shares; (2) I have had the opportunity to ask questions
concerning the Shares and the Company and all questions posed have been answered
to my satisfaction; (3) I have been given the opportunity to obtain any
additional information I deem necessary to verify the accuracy of any
information obtained concerning the Shares and the Company; and (4) I have such
knowledge and experience in financial and business matters that I am able to
evaluate the merits and risks of purchasing the Shares and to make an informed
investment decision relating thereto.

      I hereby represent and warrant that I am purchasing the Shares for my own
personal account for investment and not with a view to the sale or distribution
of all or any part of the Shares.

      I understand that because the Shares have not been registered under the
1933 Act, I must continue to bear the economic risk of the investment for an
indefinite time and the Shares cannot be sold unless the Shares are subsequently
registered under applicable federal and state securities laws or an exemption
from such registration requirements is available.

      I agree that I will in no event sell or distribute or otherwise dispose of
all or any part of the Shares unless (1) there is an effective registration
statement under the 1933 Act and applicable state securities laws covering any
such transaction involving the Shares or (2) the Company receives an opinion of
my legal counsel (concurred in by legal counsel for the

                                      A-1

<PAGE>

Company) stating that such transaction is exempt from registration or the
Company otherwise satisfies itself that such transaction is exempt from
registration.

      I consent to the placing of a legend on my certificate for the Shares
stating that the Shares have not been registered and setting forth the
restriction on transfer contemplated hereby and to the placing of a stop
transfer order on the books of the Company and with any transfer agents against
the Shares until the Shares may be legally resold or distributed without
restriction.

      I understand that at the present time Rule 144 of the Securities and
Exchange Commission (the "SEC") may not be relied on for the resale or
distribution of the Shares by me. I understand that the Company has no
obligation to me to register the sale of the Shares with the SEC and has not
represented to me that it will register the sale of the Shares.

      I understand the terms and restrictions on the right to dispose of the
Shares set forth in the 2003 Employee, Director and Consultant Stock Plan and
the Incentive Stock Option Agreement, both of which I have carefully reviewed. I
consent to the placing of a legend on my certificate for the Shares referring to
such restriction and the placing of stop transfer orders until the Shares may be
transferred in accordance with the terms of such restrictions.

      I have considered the Federal, state and local income tax implications of
the exercise of my Option and the purchase and subsequent sale of the Shares.

      I am paying the option exercise price for the Shares as follows:

                    _______________________________________

      Please issue the stock certificate for the Shares (check one):

      [ ] to me; or

      [ ] to me and ________________, as joint tenants with right of
      survivorship and mail the certificate to me at the following address:

_________________________

_________________________

_________________________

                                      A-2

<PAGE>

      My mailing address for shareholder communications, if different from the
address listed above is:

_________________________

_________________________

_________________________

                              Very truly yours,

                              _________________________________________________
                              Employee (signature)

                              _________________________________________________
                              Print Name

                              _________________________________________________
                              Date

                              _________________________________________________
                              Social Security Number

                                      A-3

<PAGE>

                                                                       Exhibit A

                  NOTICE OF EXERCISE OF INCENTIVE STOCK OPTION

                          [FORM FOR REGISTERED SHARES]

TO:   Alnylam Holding Co.

      __________________________

      __________________________


IMPORTANT NOTICE: This form of Notice of Exercise may only be used at such time
as the Company has filed a Registration Statement with the Securities and
Exchange Commission under which the issuance of the Shares for which this
exercise is being made is registered and such Registration Statement remains
effective.

Ladies and Gentlemen:

      I hereby exercise my Incentive Stock Option to purchase _________ shares
(the "Shares") of the common stock, $.0001 par value, of Alnylam Holding Co.
(the "Company"), at the exercise price of $________ per share, pursuant to and
subject to the terms of that certain Incentive Stock Option Agreement between
the undersigned and the Company dated _______________, 200_.

      I understand the nature of the investment I am making and the financial
risks thereof. I am aware that it is my responsibility to have consulted with
competent tax and legal advisors about the relevant national, state and local
income tax and securities laws affecting the exercise of the Option and the
purchase and subsequent sale of the Shares.

      I am paying the option exercise price for the Shares as follows:

                            _______________________

      Please issue the Shares (check one):

      [ ] to me; or

      [ ] to me and ____________________________, as joint tenants with right of
          survivorship, at the following address:

      __________________________

                                      A-1

<PAGE>

      __________________________

      __________________________

      My mailing address for shareholder communications, if different from the
address listed above, is:

      __________________________

      __________________________

      __________________________

                              Very truly yours,

                              _________________________________________________
                              Employee (signature)

                              _________________________________________________
                              Print Name

                              _________________________________________________
                              Date

                              _________________________________________________
                              Social Security Number

                                      A-2

<PAGE>

                                                                       Exhibit B

                                CONSENT OF SPOUSE

      I, ____________________________, spouse of _____________________________,
acknowledge that I have read the Incentive Stock Option Agreement dated as of
_______________, 200__ (the "Agreement") to which this Consent is attached as
Exhibit B and that I know its contents. Capitalized terms used and not defined
herein shall have the meanings assigned to such terms in the Agreement. I am
aware that by its provisions the Shares granted to my spouse pursuant to the
Agreement are subject to a right of repurchase in favor of Alnylam Holding Co.
(the "Company") and that, accordingly, the Company has the right to repurchase
up to all of the Shares of which I may become possessed as a result of a gift
from my spouse or a court decree and/or any property settlement in any domestic
litigation.

      I hereby agree that my interest, if any, in the Shares subject to the
Agreement shall be irrevocably bound by the Agreement and further understand and
agree that any community property interest I may have in the Shares shall be
similarly bound by the Agreement.

      I agree to the repurchase right described in Section 12.2 of the Agreement
and I hereby consent to the repurchase of the Shares by the Company and the sale
of the Shares by my spouse or my spouse's legal representative in accordance
with the provisions of the Agreement. Further, as part of the consideration for
the Agreement, I agree that at my death, if I have not disposed of any interest
of mine in the Shares by an outright bequest of the Shares to my spouse, then
the Company shall have the same rights against my legal representative to
exercise its rights of repurchase with respect to any interest of mine in the
Shares as it would have had pursuant to the Agreement if I had acquired the
Shares pursuant to a court decree in domestic litigation.

      I AM AWARE THAT THE LEGAL, FINANCIAL AND RELATED MATTERS CONTAINED IN THE
AGREEMENT ARE COMPLEX AND THAT I AM FREE TO SEEK INDEPENDENT PROFESSIONAL
GUIDANCE OR COUNSEL WITH RESPECT TO THIS CONSENT. I HAVE EITHER SOUGHT SUCH
GUIDANCE OR COUNSEL OR DETERMINED AFTER REVIEWING THE AGREEMENT CAREFULLY THAT I
WILL WAIVE SUCH RIGHT.

      Dated as of the _______ day of ________________, 200__.

                                        _______________________________________
                                        Print name:

                                      B-1

<PAGE>

                                                                       EXHIBIT C

                           RESTRICTED STOCK AGREEMENT

                               ALNYLAM HOLDING CO.

      AGREEMENT made as of the ___ day of ____________, 200__ (the "Grant
Date"), between Alnylam Holding Co. (the "Company"), a Delaware corporation
having its principal place of business in Cambridge, Massachusetts, and
________________ of ________________________, (the "Participant").

      WHEREAS, the Company has adopted the Alnylam Holding Co. 2003 Employee,
Director and Consultant Stock Plan (the "Plan") to promote the interests of the
Company by providing an incentive for employees, directors and consultants of
the Company or its Affiliates;

      WHEREAS, the parties hereto understand and agree that any terms used and
not defined herein have the meanings ascribed to such terms in the Plan and that
any and all references herein to employment of the Participant by the Company
shall include the Participant's employment or service as an employee, director
or consultant of the Company or any Affiliate;

      WHEREAS, pursuant to the exercise of an option granted to the Participant
pursuant to an Incentive Stock Option Agreement dated ___________ by and between
the Company and the Participant issued under the Plan (the "Option Agreement"),
which Option Agreement and Plan are hereby incorporated herein by reference, the
Participant has elected to purchase _________ shares of the Company's common
stock, $.0001 par value per share ("Common Stock"), which have not become vested
under the vesting schedule set forth in the Option Agreement (the "Unvested
Shares"). The Unvested Shares and the Shares subject to the Option Agreement
that have become vested are sometimes collectively referred to herein as the
"Shares."

      WHEREAS, as required by the Option Agreement, as a condition to the
Participant's election to exercise the option, the Participant must execute this
Agreement, which sets forth the rights and obligations of the parties with
respect to the Unvested Shares acquired upon exercise of the option pursuant to
the Option Agreement; and

      WHEREAS, Participant wishes to accept said offer in accordance with the
provisions of the Plan, all on the terms and conditions hereinafter set forth.

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

                                      C-1

<PAGE>

      1.    Company's Lapsing Repurchase Right.

      (a)   Lapsing Repurchase Right. Except as set forth in Subsection 1(b)
hereof, in the event that for any reason the Participant no longer is an
employee, director or consultant of the Company or an Affiliate, the Company (or
its designee) shall have the option, but not the obligation, to purchase from
the Participant (or the Participant's Survivor), and, in the event the Company
exercises such option, the Participant (or the Participant's Survivor) shall be
obligated to sell to the Company (or its designee), at a price per Share equal
to the Purchase Price, all or any part of the Unvested Shares determined as of
the date of such termination of service (the "Lapsing Repurchase Right"). The
Lapsing Repurchase Right with respect to the Unvested Shares shall terminate as
to such Unvested Shares in accordance with the vesting schedule set forth in
Section 3 of the Option Agreement. The Company's Lapsing Repurchase Right shall
be valid for a period of one year commencing with the date of such termination
of employment or service. Notwithstanding any other provision hereof, in the
event the Company is prohibited during such one year period from exercising its
Lapsing Repurchase Right by Section 160 of the Delaware General Corporation Law
as amended from time to time (or any successor provision), then the time period
during which such Lapsing Repurchase Right may be exercised shall be extended
until 30 days after the Company is first not so prohibited.

      (b)   Effect of Termination for Disability or upon Death. The following
rules apply if the Participant ceases to be an employee, director or consultant
of the Company, or an Affiliate, by reason of Disability or death: to the extent
the Company's Lapsing Repurchase Right has not lapsed as of the date of
Disability or death, as case may be, the Company may exercise such Lapsing
Repurchase Right; provided, however, that the Company's Lapsing Repurchase Right
shall be deemed to have lapsed to the extent of a pro rata portion of the
Unvested Shares through the date of Disability or death, as would have lapsed
had the Participant not become Disabled or died, as the case may be. The
proration shall be based upon the number of days accrued in such current vesting
period prior to the Participant's date of Disability or death, as the case may
be.

      (c)   Closing. In the event that the Company exercises the Lapsing
Repurchase Right, the Company shall notify the Participant, or, in the case of
the Participant's death, his or her Survivor, in writing of its intent to
repurchase the Unvested Shares. Such notice may be mailed by the Company up to
and including the last day of the time period provided for above for exercise of
the Lapsing Repurchase Right. The notice shall specify the place, time and date
for payment of the repurchase price (the "Closing") and the number of Unvested
Shares with respect to which the Company is exercising the Lapsing Repurchase
Right. The Closing shall be not less than ten days nor more than 60 days from
the date of mailing of the notice, and the Participant or the Participant's
Survivor with respect to the Unvested Shares which the Company elects to
repurchase shall have no further rights as the owner thereof from and after the
date specified in the notice. At the Closing, the repurchase price shall be
delivered to the Participant or the Participant's Survivor and the Unvested
Shares being repurchased, duly endorsed for transfer, shall, to the extent that
they are not then in the possession of the Company, be delivered to the Company
by the Participant or the Participant's Survivor.

      (d)   Escrow. The certificates representing all Unvested Shares acquired
by the Participant hereunder which from time to time are subject to the Lapsing
Repurchase Right shall

                                      C-2

<PAGE>

be delivered to the Company and the Company shall hold such Unvested Shares in
escrow as provided in this Subsection 1(d). Promptly following receipt by the
Company of a written request from the Participant, the Company shall release
from escrow and deliver to the Participant a certificate for the whole number of
Unvested Shares, if any, as to which the Company's Lapsing Repurchase Right has
lapsed. In the event of a repurchase by the Company of Unvested Shares subject
to the Lapsing Repurchase Right, the Company shall release from escrow and
cancel a certificate for the number of Unvested Shares so repurchased. Any
securities distributed in respect of the Unvested Shares held in escrow,
including, without limitation, shares issued as a result of stock splits, stock
dividends or other recapitalizations, shall also be held in escrow in the same
manner as the Unvested Shares.

      (e)   Prohibition on Transfer. The Participant recognizes and agrees that
all Unvested Shares which are subject to the Lapsing Repurchase Right may not be
sold, transferred, assigned, hypothecated, pledged, encumbered or otherwise
disposed of, whether voluntarily or by operation of law, other than to the
Company (or its designee). The Company shall not be required to transfer any
Unvested Shares on its books which shall have been sold, assigned or otherwise
transferred in violation of this Subsection 1(e), or to treat as the owner of
such Unvested Shares, or to accord the right to vote as such owner or to pay
dividends to, any person or organization to which any such Unvested Shares shall
have been so sold, assigned or otherwise transferred, in violation of this
Subsection 1(e). The Participant further recognizes and agrees that all Shares
remain subject to Section 12 of the Option Agreement, except that with respect
to the Unvested Shares subject to the Lapsing Repurchase Right, this Agreement
will supercede Section 12.3 of the Option Agreement.

      (f)   Failure to Deliver Unvested Shares to be Repurchased. In the event
that the Unvested Shares to be repurchased by the Company under this Agreement
are not in the Company's possession pursuant to Subsection 1(d) above or
otherwise and the Participant or the Participant's Survivor fails to deliver
such Unvested Shares to the Company (or its designee), the Company may elect (i)
to establish a segregated account in the amount of the repurchase price, such
account to be turned over to the Participant or the Participant's Survivor upon
delivery of such Unvested Shares, and (ii) immediately to take such action as is
appropriate to transfer record title of such Unvested Shares from the
Participant to the Company (or its designee) and to treat the Participant and
such Unvested Shares in all respects as if delivery of such Unvested Shares had
been made as required by this Agreement. The Participant hereby irrevocably
grants the Company a power of attorney which shall be coupled with an interest
for the purpose of effectuating the preceding sentence.

      (g)   Adjustments. The Plan and the Option Agreement contain provisions
covering the treatment of Shares in a number of contingencies such as stock
splits and mergers. Provisions in the Plan and the Option Agreement for
adjustment with respect to the Shares and the related provisions with respect to
successors to the business of the Company are hereby made applicable hereunder
and are incorporated herein by reference.

      2.    Legend. In addition to any legend required pursuant to the Plan or
the Option Agreement, all certificates representing the Unvested Shares to be
issued to the Participant pursuant to this Agreement shall have endorsed thereon
a legend substantially as follows:

                                      C-3

<PAGE>

      "The shares represented by this certificate are subject to restrictions
      set forth in a Restricted Stock Agreement dated as of ____________, 200__
      with this Company, a copy of which Agreement is available for inspection
      at the offices of the Company or will be made available upon request."

      3.    Purchase for Investment. If the offering and sale of the Unvested
Shares have not been effectively registered under the Securities Act of 1933, as
amended, the Participant hereby represents and warrants that he or she is
acquiring the Unvested Shares for his or her own account, for investment, and
not with a view to, or for sale in connection with, the distribution of any such
Unvested Shares.

      4.    Provisions of Agreement Controlling. The Participant specifically
understands and agrees that the Unvested Shares issued under the Plan are being
sold to the Participant pursuant to the Plan and the Option Agreement, a copy of
which Plan and Option Agreement the Participant acknowledges he or she has read
and understands and by which Plan and Option Agreement he or she agrees to be
bound. The provisions of the Plan and the Option Agreement are incorporated
herein by reference. In the event of a conflict between the terms and conditions
of the Plan, this Agreement and the Option Agreement, the provisions of this
Agreement will control.

      5.    Tax Liability of the Participant and Payment of Taxes. The
Participant acknowledges and agrees that any income or other taxes due from the
Participant with respect to the Unvested Shares issued pursuant to this
Agreement, including, without limitation, the Lapsing Repurchase Right, shall be
the Participant's responsibility. Without limiting the foregoing, the
Participant agrees that, to the extent that the lapsing of restrictions on
disposition of any of the Unvested Shares or the declaration of dividends on any
such shares before the lapse of such restrictions on disposition results in the
Participant's being deemed to be in receipt of earned income under the
provisions of the Code, the Company shall be entitled to immediate payment from
the Participant of the amount of any tax required to be withheld by the Company.

      Upon execution of this Agreement, the Participant may file an election
under Section 83 of the Code in substantially the form attached as Attachment I.
The Participant acknowledges that if she does not file such an election, as the
Unvested Shares are released from the Lapsing Repurchase Right in accordance
with Section 1, the Participant may have income for tax purposes equal to the
fair market value of the Unvested Shares at such date, less the price paid for
the Unvested Shares by the Participant.

      6.    Securities Law Compliance. The Participant specifically acknowledges
and agrees that any sales of Unvested Shares shall be made in accordance with
the requirements of the Securities Act of 1933, as amended, in a transaction as
to which the Company shall have received an opinion of counsel satisfactory to
it confirming such compliance.

      7.    Equitable Relief. The Participant specifically acknowledges and
agrees that in the event of a breach or threatened breach of the provisions of
this Agreement, the Option Agreement or the Plan, including the attempted
transfer of the Unvested Shares by the

                                      C-4

<PAGE>

Participant in violation of this Agreement or the Option Agreement, monetary
damages may not be adequate to compensate the Company, and, therefore, in the
event of such a breach or threatened breach, in addition to any right to
damages, the Company shall be entitled to equitable relief in any court having
competent jurisdiction. Nothing herein shall be construed as prohibiting the
Company from pursuing any other remedies available to it for any such breach or
threatened breach.

      8.    No Obligation to Maintain Relationship. The Company is not by the
Plan, the Option Agreement or this Agreement obligated to continue the
Participant as an employee, director or consultant of the Company, or an
Affiliate. The Participant acknowledges: (i) that the Plan is discretionary in
nature and may be suspended or terminated by the Company at any time; (ii) that
the grant of the Shares is a one-time benefit which does not create any
contractual or other right to receive future grants of shares, or benefits in
lieu of shares; (iii) that all determinations with respect to any such future
grants, including, but not limited to, the times when shares shall be granted,
the number of shares to be granted, the Purchase Price, and the time or times
when each share shall be free from the Lapsing Repurchase Right, will be at the
sole discretion of the Company; (iv) that the Participant's participation in the
Plan is voluntary; (v) that the value of the Shares is an extraordinary item of
compensation which is outside the scope of the Participant's employment
contract, if any; and (vi) that the Shares are not part of normal or expected
compensation for purposes of calculating any severance, resignation, redundancy,
end of service payments, bonuses, long-service awards, pension or retirement
benefits or similar payments.

      9.    Notices. Any notices required or permitted by the terms of this
Agreement, the Option Agreement or the Plan shall be given by recognized courier
service, facsimile, registered or certified mail, return receipt requested,
addressed as follows:

      If to the Company:

                             Alnylam Holding Co.

                             _____________________________________

                             _____________________________________

      If to the Participant:
                             _____________________________________

                             _____________________________________

                             _____________________________________


or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given on the
earliest of receipt, one business day following delivery by the sender to a
recognized courier service, or three business days following mailing by
registered or certified mail.

                                      C-5

<PAGE>

      10.   Binding Effect. This Agreement shall be for the benefit of and shall
be binding upon the parties hereto, upon their respective successors and assigns
and upon the Participant's heirs, executors, administrators.

      11.   Governing Law. This Agreement shall be construed and enforced in
accordance with the laws of the State of Delaware, without giving effect to the
conflict of law principles thereof. For the purpose of litigating any dispute
that arises under this Agreement, whether at law or in equity, the parties
hereby consent to exclusive jurisdiction in Massachusetts and agree that such
litigation shall be conducted in the courts of Suffolk County, Massachusetts or
the federal courts of the United States for the District of Massachusetts.

      12.   Severability. If any provision of this Agreement is held to be
invalid or unenforceable by a court of competent jurisdiction, then such
provision or provisions shall be modified to the extent necessary to make such
provision valid and enforceable, and to the extent that this is impossible, then
such provision shall be deemed to be excised from this Agreement, and the
validity, legality and enforceability of the rest of this Agreement shall not be
affected thereby.

      13.   Entire Agreement. This Agreement, together with the Plan and the
Option Agreement, constitutes the entire agreement and understanding between the
parties hereto with respect to the subject matter hereof and supersedes all
prior oral or written agreements and understandings relating to the subject
matter hereof. No statement, representation, warranty, covenant or agreement not
expressly set forth in this Agreement, the Option Agreement or the Plan shall
affect or be used to interpret, change or restrict the express terms and
provisions of this Agreement provided, however, in any event, this Agreement
shall be subject to and governed by the Plan.

      14.   Modifications and Amendments; Waivers and Consents. The terms and
provisions of this Agreement may be modified or amended as provided in the Plan.
Except as provided in the Plan, the terms and provisions of this Agreement may
be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be
effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

      15.   Consent of Spouse. If the Participant is married as of the date of
this Agreement, the Participant's spouse shall execute a Consent of Spouse in
the form of Attachment II hereto, effective as of the date hereof. Such consent
shall not be deemed to confer or convey to the spouse any rights in the Unvested
Shares that do not otherwise exist by operation of law or the agreement of the
parties. If the Participant marries or remarries subsequent to the date hereof,
the Participant shall, not later than 60 days thereafter, obtain his or her new
spouse's acknowledgement of and consent to the existence and binding effect of
all restrictions contained in this Agreement by such spouse's executing and
delivering a Consent of Spouse in the form of Attachment II.

                                      C-6

<PAGE>

      16.   Counterparts. This Agreement may be executed in one or more
counterparts, and by different parties hereto on separate counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

      17.   Data Privacy. By entering into this Agreement, the Participant: (i)
authorizes the Company and each Affiliate, and any agent of the Company or any
Affiliate administering the Plan or providing Plan record keeping services, to
disclose to the Company or any of its Affiliates such information and data as
the Company or any such Affiliate shall request in order to facilitate the grant
of Shares and the administration of the Plan; (ii) waives any data privacy
rights he or she may have with respect to such information; and (iii) authorizes
the Company and each Affiliate to store and transmit such information in
electronic form.

                      [THE NEXT PAGE IS THE SIGNATURE PAGE]

                                      C-7

<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

                               ALNYLAM HOLDING CO.

                               By:______________________________________________
                               Name:
                               Title:

                               PARTICIPANT:

                               _________________________________________________
                               Print name:

                                      C-8
<PAGE>

                                                                    ATTACHMENT I

                    ELECTION TO INCLUDE GROSS INCOME IN YEAR
                      OF TRANSFER PURSUANT TO SECTION 83(b)
                OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED

      In accordance with Section 83(b) of the Internal Revenue Code of 1986, as
amended (the "Code"), the undersigned hereby elects to include in his gross
income as compensation for services the excess, if any, of the fair market value
of the property (described below) at the time of transfer over the amount paid
for such property.

The following sets for the information required in accordance with the Code and
the regulations promulgated hereunder:

1.    The name, address and social security number of the undersigned are:

            Name:
            Address:
            Social Security No.:

2.    The description of the property with respect to which the election is
      being made is as follows:

      ____________ (___) shares (the "Shares") of Common Stock, $.0001 par value
      per share, of Alnylam Holding Co., a Delaware corporation (the "Company").

3.    This election is made for the calendar year ____, with respect to the
      transfer of the property to the Taxpayer on _________________.

4.    Description of restrictions: The property is subject to the following
      restrictions:

      In the event taxpayer's employment with the Company or an Affiliate is
      terminated, the Company may repurchase all or any portion of the Shares
      determined as set forth below at the acquisition price paid by the
      taxpayer:

      A.    If the termination takes place prior to the First Anniversary Date,
            the Purchase Option will apply to all of the Shares.

      B.    If the termination takes place after the First Anniversary Date, the
            number of Shares to which the Purchase Option applies shall be the
            Total Shares less (i) the amount of Total Shares vested on the First
            Anniversary Date and (ii)  ___________________ of the Total Shares
            for each period ending each _____, _____, _____ and _____ after the
            First Anniversary Date if the taxpayer is employed by the Company
            or an Affiliate.

                                       I-1
<PAGE>

5.    The fair market value at time of transfer (determined without regard to
      any restrictions other than restrictions which by their terms will never
      lapse) of the property with respect to which this election is being made
      was not more than $____ per Share.

6.    The amount paid by taxpayer for said property was $___ per Share.

7.    A copy of this statement has been furnished to the Company.

Signed this ____ day of ______, 200_.

                                             ___________________________________
                                             Print Name:

                                       I-2
<PAGE>

                                                                   ATTACHMENT II

                                CONSENT OF SPOUSE

      I, ____________________________, spouse of _____________________________,
acknowledge that I have read the RESTRICTED STOCK AGREEMENT dated as of
_______________, 200__ (the "Agreement") to which this Consent is attached as
Attachment II and that I know its contents. Capitalized terms used and not
defined herein shall have the meanings assigned to such terms in the Agreement.
I am aware that by its provisions the Unvested Shares granted to my spouse
pursuant to the Agreement are subject to a Lapsing Repurchase Right in favor of
Alnylam Holding Co. (the "Company") and that, accordingly, the Company has the
right to repurchase up to all of the Unvested Shares of which I may become
possessed as a result of a gift from my spouse or a court decree and/or any
property settlement in any domestic litigation.

      I hereby agree that my interest, if any, in the Unvested Shares subject to
the Agreement shall be irrevocably bound by the Agreement and further understand
and agree that any community property interest I may have in the Unvested Shares
shall be similarly bound by the Agreement.

      I agree to the Lapsing Repurchase Right described in the Agreement and I
hereby consent to the repurchase of the Unvested Shares by the Company and the
sale of the Unvested Shares by my spouse or my spouse's legal representative in
accordance with the provisions of the Agreement. Further, as part of the
consideration for the Agreement, I agree that at my death, if I have not
disposed of any interest of mine in the Unvested Shares by an outright bequest
of the Unvested Shares to my spouse, then the Company shall have the same rights
against my legal representative to exercise its rights of repurchase with
respect to any interest of mine in the Unvested Shares as it would have had
pursuant to the Agreement if I had acquired the Unvested Shares pursuant to a
court decree in domestic litigation.

      I AM AWARE THAT THE LEGAL, FINANCIAL AND RELATED MATTERS CONTAINED IN THE
AGREEMENT ARE COMPLEX AND THAT I AM FREE TO SEEK INDEPENDENT PROFESSIONAL
GUIDANCE OR COUNSEL WITH RESPECT TO THIS CONSENT. I HAVE EITHER SOUGHT SUCH
GUIDANCE OR COUNSEL OR DETERMINED AFTER REVIEWING THE AGREEMENT CAREFULLY THAT I
WILL WAIVE SUCH RIGHT.

      Dated as of the _______ day of ________________, 200__.

                                                ________________________________
                                                Print name:

                                      II-1
<PAGE>

                      NON-QUALIFIED STOCK OPTION AGREEMENT

                               ALNYLAM HOLDING CO.

      AGREEMENT made as of the ___ day of ______ ____, between Alnylam Holding
Co. (the "Company"), a Delaware corporation having a principal place of business
in Cambridge, Massachusetts, and _______________ of ___________ (the
"Participant").

      WHEREAS, the Company desires to grant to the Participant an Option to
purchase shares of its common stock, $.0001 par value per share (the "Shares"),
under and for the purposes set forth in the Company's 2003 Employee, Director
and Consultant Stock Plan (the "Plan");

      WHEREAS, the Company and the Participant understand and agree that any
terms used and not defined herein have the same meanings as in the Plan; and

      WHEREAS, the Company and the Participant each intend that the Option
granted herein shall be a Non-Qualified Option.

      NOW, THEREFORE, in consideration of the mutual covenants hereinafter set
forth and for other good and valuable consideration, the parties hereto agree as
follows:

      1.    GRANT OF OPTION.

      The Company hereby grants to the Participant the right and option to
purchase all or any part of an aggregate of _______________ Shares, on the terms
and conditions and subject to all the limitations set forth herein, under United
States securities and tax laws, and in the Plan, which is incorporated herein by
reference. The Participant acknowledges receipt of a copy of the Plan.

      2.    PURCHASE PRICE.

      The purchase price of the Shares covered by the Option shall be $___ per
Share, subject to adjustment, as provided in the Plan, in the event of a stock
split, reverse stock split or other events affecting the holders of Shares after
the date hereof (the "Purchase Price"). Payment shall be made in accordance with
Paragraph 8 of the Plan.

      3.    EXERCISABILITY OF OPTION.

      Subject to the terms and conditions set forth in this Agreement and the
Plan, the Option granted hereby shall become exercisable for up to
____________________ of the Shares on ______________ and for an additional
____________________ of the Shares on _____, _____, _____ and _____ of each
year after the first anniversary of this Agreement until 100% of the Shares have
become vested.

      Alternatively, at the election of the Participant, the Option may be
exercised in whole or in part at any time as to Shares which have not yet vested
in accordance with the

<PAGE>

above schedule; provided however, as a condition to exercising the Option for
such unvested Shares, the Participant shall execute a Restricted Stock Agreement
in the form attached hereto as Exhibit C.

      The foregoing rights are cumulative and are subject to the other terms and
conditions of this Agreement and the Plan.

            4.    TERM OF OPTION.

      The Option shall terminate ten years from the date of this Agreement, but
shall be subject to earlier termination as provided herein or in the Plan.

      If the Participant ceases to be an employee, director or consultant of the
Company or of an Affiliate (for any reason other than the death or Disability of
the Participant or termination of the Participant for "cause" (as defined in the
Plan), the Option may be exercised, if it has not previously terminated, within
three months after the date the Participant ceases to be an employee, director
or consultant of the Company or an Affiliate, or within the originally
prescribed term of the Option, whichever is earlier, but may not be exercised
thereafter. In such event, the Option shall be exercisable only to the extent
that the Option has become exercisable and is in effect at the date of such
cessation of employment, directorship or consultancy.

      Notwithstanding the foregoing, in the event of the Participant's
Disability or death within three months after the termination of employment,
directorship or consultancy, the Participant or the Participant's Survivors may
exercise the Option within one year after the date of the Participant's
termination of employment, directorship or consultancy, but in no event after
the date of expiration of the term of the Option.

      In the event the Participant's employment, directorship or consultancy is
terminated by the Company or an Affiliate for "cause" (as defined in the Plan),
the Participant's right to exercise any unexercised portion of this Option shall
cease immediately as of the time the Participant is notified his or her
employment, directorship or consultancy is terminated for "cause", and this
Option shall thereupon terminate. Notwithstanding anything herein to the
contrary, if subsequent to the Participant's termination, but prior to the
exercise of the Option, the Board of Directors of the Company determines that,
either prior or subsequent to the Participant's termination, the Participant
engaged in conduct which would constitute "cause," then the Participant shall
immediately cease to have any right to exercise the Option and this Option shall
thereupon terminate.

      In the event of the Disability of the Participant, as determined in
accordance with the Plan, the Option shall be exercisable within one year after
the Participant's termination of service or, if earlier, within the term
originally prescribed by the Option. In such event, the Option shall be
exercisable:

      (a)   to the extent that the Option has become exercisable but has not
            been exercised as of the date of Disability; and

                                        2
<PAGE>

      (b)   in the event rights to exercise the Option accrue periodically, to
            the extent of a pro rata portion through the date of Disability of
            any additional vesting rights that would have accrued on the next
            vesting date had the Participant not become Disabled. The proration
            shall be based upon the number of days accrued in the current
            vesting period prior to the date of Disability.

      In the event of the death of the Participant while an employee, director
or consultant of the Company or of an Affiliate, the Option shall be exercisable
by the Participant's Survivors within one year after the date of death of the
Participant or, if earlier, within the originally prescribed term of the Option.
In such event, the Option shall be exercisable:

      (x)   to the extent that the Option has become exercisable but has not
            been exercised as of the date of death; and

      (y)   in the event rights to exercise the Option accrue periodically, to
            the extent of a pro rata portion through the date of death of any
            additional vesting rights that would have accrued on the next
            vesting date had the Participant not died. The proration shall be
            based upon the number of days accrued in the current vesting period
            prior to the Participant's date of death.

      5.    METHOD OF EXERCISING OPTION.

      Subject to the terms and conditions of this Agreement, the Option may be
exercised by written notice to the Company or its designee, in substantially the
form of Exhibit A attached hereto. Such notice shall state the number of Shares
with respect to which the Option is being exercised and shall be signed by the
person exercising the Option. Payment of the purchase price for such Shares
shall be made in accordance with Paragraph 8 of the Plan. The Company shall
deliver a certificate or certificates representing such Shares as soon as
practicable after the notice shall be received, provided, however, that the
Company may delay issuance of such Shares until completion of any action or
obtaining of any consent, which the Company deems necessary under any applicable
law (including, without limitation, state securities or "blue sky" laws). The
certificate or certificates for the Shares as to which the Option shall have
been so exercised shall be registered in the Company's share register in the
name of the person so exercising the Option (or, if the Option shall be
exercised by the Participant and if the Participant shall so request in the
notice exercising the Option, shall be registered in the name of the Participant
and another person jointly, with right of survivorship) and shall be delivered
as provided above to or upon the written order of the person exercising the
Option. In the event the Option shall be exercised, pursuant to Section 4
hereof, by any person other than the Participant, such notice shall be
accompanied by appropriate proof of the right of such person to exercise the
Option. All Shares that shall be purchased upon the exercise of the Option as
provided herein shall be fully paid and nonassessable.

                                        3
<PAGE>

      6.    PARTIAL EXERCISE.

      Exercise of this Option to the extent above stated may be made in part at
any time and from time to time within the above limits, except that no
fractional share shall be issued pursuant to this Option.

      7.    NON-ASSIGNABILITY.

      The Option shall not be transferable by the Participant otherwise than by
will or by the laws of descent and distribution or pursuant to a qualified
domestic relations order as defined by the Code or Title I of the Employee
Retirement Income Security Act or the rules thereunder. However, the
Participant, with the approval of the Administrator, may transfer the Option for
no consideration to or for the benefit of the Participant's Immediate Family
(including, without limitation, to a trust for the benefit of the Participant's
Immediate Family or to a partnership or limited liability company for one or
more members of the Participant's Immediate Family), subject to such limits as
the Administrator may establish, and the transferee shall remain subject to all
the terms and conditions applicable to the Option prior to such transfer and
each such transferee shall so acknowledge in writing as a condition precedent to
the effectiveness of such transfer. The term "Immediate Family" shall mean the
Participant's spouse, former spouse, parents, children, stepchildren, adoptive
relationships, sisters, brothers, nieces, nephews and grandchildren (and, for
this purpose, shall also include the Participant.) Except as provided in the
previous sentence, the Option shall be exercisable, during the Participant's
lifetime, only by the Participant (or, in the event of legal incapacity or
incompetency, by the Participant's guardian or representative) and shall not be
assigned, pledged or hypothecated in any way (whether by operation of law or
otherwise) and shall not be subject to execution, attachment or similar process.
Any attempted transfer, assignment, pledge, hypothecation or other disposition
of the Option or of any rights granted hereunder contrary to the provisions of
this Section 7, or the levy of any attachment or similar process upon the Option
shall be null and void.

      8.    NO RIGHTS AS STOCKHOLDER UNTIL EXERCISE.

      The Participant shall have no rights as a stockholder with respect to
Shares subject to this Agreement until registration of the Shares in the
Company's share register in the name of the Participant. Except as is expressly
provided in the Plan with respect to certain changes in the capitalization of
the Company, no adjustment shall be made for dividends or similar rights for
which the record date is prior to the date of such registration.

      9.    ADJUSTMENTS.

      The Plan contains provisions covering the treatment of Options in a number
of contingencies such as stock splits and mergers. Provisions in the Plan for
adjustment with respect to stock subject to Options and the related provisions
with respect to successors to the business of the Company are hereby made
applicable hereunder and are incorporated herein by reference, provided,
however, in the event of a Change of Control (as defined in the Plan) which the
Administrator (as defined in the Plan) or the Successor Board (as defined in the
Plan) makes provisions for the treatment of Options under (A) clause (i) of

                                        4
<PAGE>

the first paragraph of Section 23(B) of the Plan, an additional one-sixteenth
(1/16) of the Shares shall become fully vested and immediately exercisable
immediately prior to such Change of Control and the remaining Shares which have
not vested shall vest in accordance with Section 3 above, provided, however, if
the Participant's employment with the Company is Terminated (as defined below),
fifty percent (50%) of the Shares which have not yet vested in accordance with
Section 3 above shall become fully vested and immediately exercisable
immediately prior to such termination (for purposes of this Section 9, the
Participant shall be deemed to have been "Terminated" if at any time before the
six-month anniversary of the closing of such Change of Control, (i) the
Participant shall fail to be vested with power and authority analogous to the
Participant's title and/or office prior to such Change of Control, (ii) the
Participant shall lose any significant duties or responsibilities attending such
office, (iii) there shall occur a reduction in the Participant's base
compensation, or (iv) the Participant's employment with the Company or an
Affiliate, or its successor, is terminated without "cause" (as defined in the
Plan)) or (B) either clause (ii) or (iii) of the first paragraph of Section
23(B) of the Plan, all Shares under this Option shall become fully vested and
immediately exercisable prior to such Change of Control.

      10.   TAXES.

      The Participant acknowledges that upon exercise of the Option the
Participant will be deemed to have taxable income measured by the difference
between the then fair market value of the Shares received upon exercise and the
price paid for such Shares pursuant to this Agreement. The Participant
acknowledges that any income or other taxes due from him or her with respect to
this Option or the Shares issuable pursuant to this Option shall be the
Participant's responsibility.

      The Participant agrees that the Company may withhold from the
Participant's remuneration, if any, the minimum statutory amount of federal,
state and local withholding taxes attributable to such amount that is considered
compensation includable in such person's gross income. At the Company's
discretion, the amount required to be withheld may be withheld in cash from such
remuneration, or in kind from the Shares otherwise deliverable to the
Participant on exercise of the Option. The Participant further agrees that, if
the Company does not withhold an amount from the Participant's remuneration
sufficient to satisfy the Company's income tax withholding obligation, the
Participant will reimburse the Company on demand, in cash, for the amount
under-withheld.

      11.   PURCHASE FOR INVESTMENT.

      Unless the offering and sale of the Shares to be issued upon the
particular exercise of the Option shall have been effectively registered under
the Securities Act of 1933, as now in force or hereafter amended (the "1933
Act"), the Company shall be under no obligation to issue the Shares covered by
such exercise unless and until the following conditions have been fulfilled:

         (a)      The person(s) who exercise the Option shall warrant to the
                  Company, at the time of such exercise, that such person(s) are
                  acquiring such Shares for their own respective accounts, for
                  investment, and not with a view to, or for sale in connection
                  with, the distribution of any such Shares, in which event the

                                        5
<PAGE>

                  person(s) acquiring such Shares shall be bound by the
                  provisions of the following legend which shall be endorsed
                  upon the certificate(s) evidencing the Shares issued pursuant
                  to such exercise:

                        "The shares represented by this certificate have been
                        taken for investment and they may not be sold or
                        otherwise transferred by any person, including a
                        pledgee, unless (1) either (a) a Registration Statement
                        with respect to such shares shall be effective under the
                        Securities Act of 1933, as amended, or (b) the Company
                        shall have received an opinion of counsel satisfactory
                        to it that an exemption from registration under such Act
                        is then available, and (2) there shall have been
                        compliance with all applicable state securities laws;"
                        and

            (b)   If the Company so requires, the Company shall have received an
                  opinion of its counsel that the Shares may be issued upon such
                  particular exercise in compliance with the 1933 Act without
                  registration thereunder. Without limiting the generality of
                  the foregoing, the Company may delay issuance of the Shares
                  until completion of any action or obtaining of any consent,
                  which the Company deems necessary under any applicable law
                  (including without limitation state securities or "blue sky"
                  laws).

      12.   RESTRICTIONS ON TRANSFER OF SHARES.

      12.1  The Shares acquired by the Participant pursuant to the exercise of
the Option granted hereby shall not be transferred by the Participant except as
permitted herein.

      12.2  In the event of the Participant's termination of service for any
reason, the Company shall have the option, but not the obligation, to repurchase
all or any part of the Shares issued pursuant to this Agreement (including,
without limitation, Shares purchased after termination of employment, Disability
or death in accordance with Section 4 hereof). In the event the Company does
not, upon the termination of service of the Participant (as described above),
exercise its option pursuant to this Section 12.2, the restrictions set forth in
the balance of this Agreement shall not thereby lapse, and the Participant for
himself or herself, his or her heirs, legatees, executors, administrators and
other successors in interest, agrees that the Shares shall remain subject to
such restrictions. The following provisions shall apply to a repurchase under
this Section 12.2:

      (i)   The per share repurchase price of the Shares to be sold to the
            Company upon exercise of its option under this Section 12.2 shall be
            equal to the Fair Market Value of each such Share determined in
            accordance with the Plan as of the date of termination of service.
            provided, however, in the event of a termination by the Company for
            "cause" (as defined in the Plan), the per share repurchase price of
            the Shares to be sold to the Company upon exercise of its option
            under this Section 12.2 shall be equal to the Purchase Price.

                                        6
<PAGE>

      (ii)  The Company's option to repurchase the Participant's Shares in the
            event of termination of service shall be valid for a period of 12
            months commencing with the date of such termination of service

      (iii) In the event the Company shall be entitled to and shall elect to
            exercise its option to repurchase the Participant's Shares under
            this Section 12.2, the Company shall notify the Participant, or in
            case of death, his or her Survivor, in writing of its intent to
            repurchase the Shares. Such written notice may be mailed by the
            Company up to and including the last day of the time period provided
            for in Section 12.2(ii) for exercise of the Company's option to
            repurchase.

      (iv)  The written notice to the Participant shall specify the address at,
            and the time and date on, which payment of the repurchase price is
            to be made (the "Closing"). The date specified shall not be less
            than ten days nor more than 60 days from the date of the mailing of
            the notice, and the Participant or his or her successor in interest
            with respect to the Shares shall have no further rights as the owner
            thereof from and after the date specified in the notice. At the
            Closing, the repurchase price shall be delivered to the Participant
            or his or her successor in interest and the Shares being purchased,
            duly endorsed for transfer, shall, to the extent that they are not
            then in the possession of the Company, be delivered to the Company
            by the Participant or his or her successor in interest.

      12.3  It shall be a condition precedent to the validity of any sale or
other transfer of any Shares by the Participant that the following restrictions
be complied with (except as hereinafter otherwise provided):

      (i)   No Shares owned by the Participant may be sold, pledged or otherwise
            transferred (including by gift or devise) to any person or entity,
            voluntarily, or by operation of law, except in accordance with the
            terms and conditions hereinafter set forth.

      (ii)  Before selling or otherwise transferring all or part of the Shares,
            the Participant shall give written notice of such intention to the
            Company, which notice shall include the name of the proposed
            transferee, the proposed purchase price per share, the terms of
            payment of such purchase price and all other matters relating to
            such sale or transfer and shall be accompanied by a copy of the
            binding written agreement of the proposed transferee to purchase the
            Shares of the Participant. Such notice shall constitute a binding
            offer by the Participant to sell to the Company such number of the
            Shares then held by the Participant as are proposed to be sold in
            the notice at the monetary price per share designated in such
            notice, payable on the terms offered to the Participant by the
            proposed transferee (provided, however, that the Company shall not
            be required to meet any non-monetary terms of the proposed transfer,
            including, without limitation, delivery of other securities in
            exchange for the Shares proposed to be sold). The Company shall give
            written notice to the Participant as to whether such offer has been
            accepted in whole by the Company within sixty days after its receipt
            of

                                        7
<PAGE>

            written notice from the Participant. The Company may only accept
            such offer in whole and may not accept such offer in part. Such
            acceptance notice shall fix a time, location and date for the
            closing on such purchase ("Closing Date") which shall not be less
            than ten nor more than sixty days after the giving of the acceptance
            notice. The place for such closing shall be at the Company's
            principal office. At such closing, the Participant shall accept
            payment as set forth herein and shall deliver to the Company in
            exchange therefor certificates for the number of Shares stated in
            the notice accompanied by duly executed instruments of transfer.

      (iii) If the Company shall fail to accept any such offer, the Participant
            shall be free to sell all, but not less than all, of the Shares set
            forth in his or her notice to the designated transferee at the price
            and terms designated in the Participant's notice, provided that (i)
            such sale is consummated within six months after the giving of
            notice by the Participant to the Company as aforesaid, and (ii) the
            transferee first agrees in writing to be bound by the provisions of
            this Section 12 so that such transferee (and all subsequent
            transferees) shall thereafter only be permitted to sell or transfer
            the Shares in accordance with the terms hereof. After the expiration
            of such six months, the provisions of this Section 12.3 shall again
            apply with respect to any proposed voluntary transfer of the
            Participant's Shares.

      (iv)  The restrictions on transfer contained in this Section 12.3 shall
            not apply to (a) transfers by the Participant to his or her spouse
            or children or to a trust for the benefit of his or her spouse or
            children, (b) transfers by the Participant to his or her guardian or
            conservator, and (c) or transfers by the Participant, in the event
            of his or her death, to his or her executor(s) or administrator(s)
            or to trustee(s) under his or her will (collectively, "Permitted
            Transferees"); provided however, that in any such event the Shares
            so transferred in the hands of each such Permitted Transferee shall
            remain subject to this Agreement, and each such Permitted Transferee
            shall so acknowledge in writing as a condition precedent to the
            effectiveness of such transfer.

      (v)   The provisions of this Section 12.3 may be waived by the Company.
            Any such waiver may be unconditional or based upon such conditions
            as the Company may impose.

      12.4  In the event that the Participant or his or her successor in
interest fails to deliver the Shares to be repurchased by the Company under this
Agreement, the Company may elect (a) to establish a segregated account in the
amount of the repurchase price, such account to be turned over to the
Participant or his or her successor in interest upon delivery of such Shares,
and (b) immediately to take such action as is appropriate to transfer record
title of such Shares from the Participant to the Company and to treat the
Participant and such Shares in all respects as if delivery of such Shares had
been made as required by this Agreement. The Participant hereby irrevocably
grants the Company a power of attorney which shall be coupled with an interest
for the purpose of effectuating the preceding sentence.

                                        8
<PAGE>

      12.5  If the Company shall pay a stock dividend or declare a stock split
on or with respect to any of its Common Stock, or otherwise distribute
securities of the Company to the holders of its Common Stock, the number of
shares of stock or other securities of Company issued with respect to the shares
then subject to the restrictions contained in this Agreement shall be added to
the Shares subject to the Company's rights to repurchase pursuant to this
Agreement. If the Company shall distribute to its stockholders shares of stock
of another corporation, the shares of stock of such other corporation,
distributed with respect to the Shares then subject to the restrictions
contained in this Agreement, shall be added to the Shares subject to the
Company's rights to repurchase pursuant to this Agreement.

      12.6  If the outstanding shares of Common Stock of the Company shall be
subdivided into a greater number of shares or combined into a smaller number of
shares, or in the event of a reclassification of the outstanding shares of
Common Stock of the Company, or if the Company shall be a party to a merger,
consolidation or capital reorganization, there shall be substituted for the
Shares then subject to the restrictions contained in this Agreement such amount
and kind of securities as are issued in such subdivision, combination,
reclassification, merger, consolidation or capital reorganization in respect of
the Shares subject immediately prior thereto to the Company's rights to
repurchase pursuant to this Agreement.

      12.7  The Company shall not be required to transfer any Shares on its
books which shall have been sold, assigned or otherwise transferred in violation
of this Agreement, or to treat as owner of such Shares, or to accord the right
to vote as such owner or to pay dividends to, any person or organization to
which any such Shares shall have been so sold, assigned or otherwise
transferred, in violation of this Agreement.

      12.8  The provisions of Sections 12.1, 12.2 and 12.3 shall terminate upon
the consummation of a public offering of any of the Company's securities
pursuant to a registration statement filed with the Securities and Exchange
Commission pursuant to the 1933 Act.

      12.9  If, in connection with a registration statement filed by the Company
pursuant to the 1933 Act, the Company or its underwriter so requests, the
Participant will agree not to sell any Shares for a period not to exceed 180
days following the effectiveness of such registration.

      12.10 The Participant acknowledges and agrees that neither the Company,
its shareholders nor its directors and officers, has any duty or obligation to
disclose to the Participant any material information regarding the business of
the Company or affecting the value of the Shares before, at the time of, or
following a termination of the employment of the Participant by the Company,
including, without limitation, any information concerning plans for the Company
to make a public offering of its securities or to be acquired by or merged with
or into another firm or entity.

      12.11 All certificates representing the Shares to be issued to the
Participant pursuant to this Agreement shall have endorsed thereon a legend
substantially as follows: "The shares represented by this certificate are
subject to restrictions set forth in a Non-Qualified Stock Option Agreement
dated ___________ with this Company, a copy of which Agreement is available for
inspection at the offices of the Company or will be made available upon
request."

                                        9
<PAGE>

      13.   NO OBLIGATION TO MAINTAIN RELATIONSHIP.

      The Company is not by the Plan or this Option obligated to continue the
Participant as an employee, director or consultant of the Company or an
Affiliate. The Participant acknowledges: (i) that the Plan is discretionary in
nature and may be suspended or terminated by the Company at any time; (ii) that
the grant of the Option is a one-time benefit which does not create any
contractual or other right to receive future grants of options, or benefits in
lieu of options; (iii) that all determinations with respect to any such future
grants, including, but not limited to, the times when options shall be granted,
the number of shares subject to each option, the option price, and the time or
times when each option shall be exercisable, will be at the sole discretion of
the Company; (iv) that the Participant's participation in the Plan is voluntary;
(v) that the value of the Option is an extraordinary item of compensation which
is outside the scope of the Participant's employment contract, if any; and (vi)
that the Option is not part of normal or expected compensation for purposes of
calculating any severance, resignation, redundancy, end of service payments,
bonuses, long-service awards, pension or retirement benefits or similar
payments.

      14.   NOTICES.

      Any notices required or permitted by the terms of this Agreement or the
Plan shall be given by recognized courier service, facsimile, registered or
certified mail, return receipt requested, addressed as follows:

If to the Company:

                              Alnylam Holding Co.
                              Attn: VP Finance
                              790 Memorial Drive, Suite 202
                              Cambridge, MA 02139

If to the Participant:

                              _____________________________________

                              _____________________________________

                              _____________________________________

or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given upon
the earlier of receipt, one business day following delivery to a recognized
courier service or three business days following mailing by registered or
certified mail.

      15.   GOVERNING LAW.

      This Agreement shall be construed and enforced in accordance with the law
of the State of Delaware, without giving effect to the conflict of law
principles thereof. For the purpose of litigating any dispute that arises under
this Agreement, the parties hereby

                                       10
<PAGE>

consent to exclusive jurisdiction in Massachusetts and agree that such
litigation shall be conducted in the courts of Suffolk County, Massachusetts or
the federal courts of the United States for the District of Massachusetts.

      16.   BENEFIT OF AGREEMENT.

      Subject to the provisions of the Plan and the other provisions hereof,
this Agreement shall be for the benefit of and shall be binding upon the heirs,
executors, administrators, successors and assigns of the parties hereto.

      17.   ENTIRE AGREEMENT.

      This Agreement, together with the Plan, embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior oral or written agreements and understandings
relating to the subject matter hereof. No statement, representation, warranty,
covenant or agreement not expressly set forth in this Agreement shall affect or
be used to interpret, change or restrict, the express terms and provisions of
this Agreement, provided, however, in any event, this Agreement shall be subject
to and governed by the Plan.

      18.   MODIFICATIONS AND AMENDMENTS.

      The terms and provisions of this Agreement may be modified or amended as
provided in the Plan.

      19.   WAIVERS AND CONSENTS.

      Except as provided in the Plan, the terms and provisions of this Agreement
may be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be
effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

      20.   DATA PRIVACY.

      By entering into this Agreement, the Participant: (i) authorizes the
Company and each Affiliate, and any agent of the Company or any Affiliate
administering the Plan or providing Plan record keeping services, to disclose to
the Company or any of its Affiliates such information and data as the Company or
any such Affiliate shall request in order to facilitate the grant of options and
the administration of the Plan; (ii) waives any data privacy rights he or she
may have with respect to such information; and (iii) authorizes the Company and
each Affiliate to store and transmit such information in electronic form.

      21.   CONSENT OF SPOUSE.

                                       11
<PAGE>

      If the Participant is married as of the date of this Agreement, the
Participant's spouse shall execute a Consent of Spouse in the form of Exhibit B
hereto, effective as of the date hereof. Such consent shall not be deemed to
confer or convey to the spouse any rights in the Shares that do not otherwise
exist by operation of law or the agreement of the parties. If the Participant
marries or remarries subsequent to the date hereof, the Participant shall, not
later than 60 days thereafter, obtain his or her new spouse's acknowledgement of
and consent to the existence and binding effect of Section 12.2 of this
Agreement by such spouse's executing and delivering a Consent of Spouse in the
form of Exhibit B.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       12
<PAGE>

      IN WITNESS WHEREOF, the Company has caused this Agreement to be executed
by its duly authorized officer, and the Participant has hereunto set his or her
hand, all as of the day and year first above written.

                                       ALNYLAM HOLDING CO.

                                       By: _____________________________________
                                           Name:
                                           Title:

                                       _________________________________________
                                       Participant

                                       13
<PAGE>

                                                                       Exhibit A

                NOTICE OF EXERCISE OF NON-QUALIFIED STOCK OPTION

                         [FORM FOR UNREGISTERED SHARES]

To:   Alnylam Holding Co.

      __________________

      __________________


Ladies and Gentlemen:

      I hereby exercise my Non-Qualified Stock Option to purchase __________
shares (the "Shares") of the common stock, $.0001 par value, of Alnylam Holding
Co. (the "Company"), at the exercise price of $_____ per share, pursuant to and
subject to the terms of that certain Non-Qualified Stock Option Agreement
between the undersigned and the Company dated ________, 200_.

      I am aware that the Shares have not been registered under the Securities
Act of 1933, as amended (the "1933 Act"), or any state securities laws. I
understand that the reliance by the Company on exemptions under the 1933 Act is
predicated in part upon the truth and accuracy of the statements by me in this
Notice of Exercise.

      I hereby represent and warrant that (1) I have been furnished with all
information which I deem necessary to evaluate the merits and risks of the
purchase of the Shares; (2) I have had the opportunity to ask questions
concerning the Shares and the Company and all questions posed have been answered
to my satisfaction; (3) I have been given the opportunity to obtain any
additional information I deem necessary to verify the accuracy of any
information obtained concerning the Shares and the Company; and (4) I have such
knowledge and experience in financial and business matters that I am able to
evaluate the merits and risks of purchasing the Shares and to make an informed
investment decision relating thereto.

      I hereby represent and warrant that I am purchasing the Shares for my own
personal account for investment and not with a view to the sale or distribution
of all or any part of the Shares.

      I understand that because the Shares have not been registered under the
1933 Act, I must continue to bear the economic risk of the investment for an
indefinite time and the Shares cannot be sold unless the Shares are subsequently
registered under applicable federal and state securities laws or an exemption
from such registration requirements is available.

      I agree that I will in no event sell or distribute or otherwise dispose of
all or any part of the Shares unless (1) there is an effective registration
statement under the 1933 Act and applicable state securities laws covering any
such transaction involving the Shares or (2)

                                      A-1
<PAGE>

the Company receives an opinion of my legal counsel (concurred in by legal
counsel for the Company) stating that such transaction is exempt from
registration or the Company otherwise satisfies itself that such transaction is
exempt from registration.

      I consent to the placing of a legend on my certificate for the Shares
stating that the Shares have not been registered and setting forth the
restriction on transfer contemplated hereby and to the placing of a stop
transfer order on the books of the Company and with any transfer agents against
the Shares until the Shares may be legally resold or distributed without
restriction.

      I understand that at the present time Rule 144 of the Securities and
Exchange Commission (the "SEC") may not be relied on for the resale or
distribution of the Shares by me. I understand that the Company has no
obligation to me to register the sale of the Shares with the SEC and has not
represented to me that it will register the sale of the Shares.

      I understand the terms and restrictions on the right to dispose of the
Shares set forth in the 2003 Employee, Director and Consultant Stock Plan and
the Non-Qualified Stock Option Agreement, both of which I have carefully
reviewed. I consent to the placing of a legend on my certificate for the Shares
referring to such restriction and the placing of stop transfer orders until the
Shares may be transferred in accordance with the terms of such restrictions.

      I have considered the Federal, state and local income tax implications of
the exercise of my Option and the purchase and subsequent sale of the Shares.

      I am paying the option exercise price for the Shares as follows:

                    ________________________________________

      Please issue the stock certificate for the Shares (check one):

      [ ]   to me; or

      [ ]   to me and ________________, as joint tenants with right of
survivorship and mail the certificate to me at the following address:

_____________________________

_____________________________

_____________________________


                        My mailing address for shareholder communications, if
different from the address listed above is:

                                      A-2
<PAGE>

_____________________________

_____________________________

_____________________________

                                       Very truly yours,

                                       _________________________________________
                                       Participant (signature)

                                       _________________________________________
                                       Print Name

                                       _________________________________________
                                       Date

                                       _________________________________________
                                       Social Security Number

                                       A-3
<PAGE>

                                                                       Exhibit A

                          [FORM FOR REGISTERED SHARES]

                NOTICE OF EXERCISE OF NON-QUALIFIED STOCK OPTION

TO: Alnylam Holding Co.

    ___________________

    ___________________

IMPORTANT NOTICE: This form of Notice of Exercise may only be used at such time
as the Company has filed a Registration Statement with the Securities and
Exchange Commission under which the issuance of the Shares for which this
exercise is being made is registered and such Registration Statement remains
effective.

Ladies and Gentlemen:

      I hereby exercise my Non-Qualified Stock Option to purchase _________
shares (the "Shares") of the common stock, $.0001 par value, of Alnylam Holding
Co. (the "Company"), at the exercise price of $________ per share, pursuant to
and subject to the terms of that certain Non-Qualified Stock Option Agreement
between the undersigned and the Company dated _______________, 200_.

      I understand the nature of the investment I am making and the financial
risks thereof. I am aware that it is my responsibility to have consulted with
competent tax and legal advisors about the relevant national, state and local
income tax and securities laws affecting the exercise of the Option and the
purchase and subsequent sale of the Shares.

      I am paying the option exercise price for the Shares as follows:

                            ________________________

      Please issue the Shares (check one):

      [ ] to me; or

      [ ] to me and ____________________________, as joint tenants with right of
      survivorship, at the following address:

                                      A-1
<PAGE>

      __________________________________________

      __________________________________________

      __________________________________________

                        My mailing address for shareholder communications, if
different from the address listed above, is:

      __________________________________________

      __________________________________________

      __________________________________________

                                                     Very truly yours,

                                                     ___________________________
                                                     Participant (signature)

                                                     ___________________________
                                                     Print Name

                                                     ___________________________
                                                     Date

                                                     ___________________________
                                                     Social Security Number

                                      A-2
<PAGE>

                                                                       Exhibit B

                                CONSENT OF SPOUSE

      I, ____________________________, spouse of _____________________________,
acknowledge that I have read the Non-Qualified Stock Option Agreement dated as
of _______________, 200__ (the "Agreement") to which this Consent is attached as
Exhibit B and that I know its contents. Capitalized terms used and not defined
herein shall have the meanings assigned to such terms in the Agreement. I am
aware that by its provisions the Shares granted to my spouse pursuant to the
Agreement are subject to a right of repurchase in favor of Alnylam Holding Co.
(the "Company") and that, accordingly, the Company has the right to repurchase
up to all of the Shares of which I may become possessed as a result of a gift
from my spouse or a court decree and/or any property settlement in any domestic
litigation.

      I hereby agree that my interest, if any, in the Shares subject to the
Agreement shall be irrevocably bound by the Agreement and further understand and
agree that any community property interest I may have in the Shares shall be
similarly bound by the Agreement.

      I agree to the repurchase right described in Section 12.2 of the Agreement
and I hereby consent to the repurchase of the Shares by the Company and the sale
of the Shares by my spouse or my spouse's legal representative in accordance
with the provisions of the Agreement. Further, as part of the consideration for
the Agreement, I agree that at my death, if I have not disposed of any interest
of mine in the Shares by an outright bequest of the Shares to my spouse, then
the Company shall have the same rights against my legal representative to
exercise its rights of repurchase with respect to any interest of mine in the
Shares as it would have had pursuant to the Agreement if I had acquired the
Shares pursuant to a court decree in domestic litigation.

      I AM AWARE THAT THE LEGAL, FINANCIAL AND RELATED MATTERS CONTAINED IN THE
AGREEMENT ARE COMPLEX AND THAT I AM FREE TO SEEK INDEPENDENT PROFESSIONAL
GUIDANCE OR COUNSEL WITH RESPECT TO THIS CONSENT. I HAVE EITHER SOUGHT SUCH
GUIDANCE OR COUNSEL OR DETERMINED AFTER REVIEWING THE AGREEMENT CAREFULLY THAT I
WILL WAIVE SUCH RIGHT.

      Dated as of the _______ day of ________________, 200__.

                                        ________________________________________
                                        Print name:

                                      B-1
<PAGE>

                                                                       EXHIBIT C

                           RESTRICTED STOCK AGREEMENT

                               ALNYLAM HOLDING CO.

      AGREEMENT made as of the ___ day of ____________, 200__ (the "Grant
Date"), between Alnylam Holding Co. (the "Company"), a Delaware corporation
having its principal place of business in Cambridge, Massachusetts, and
________________ of ________________________, (the "Participant").

      WHEREAS, the Company has adopted the Alnylam Holding Co. 2003 Employee,
Director and Consultant Stock Plan (the "Plan") to promote the interests of the
Company by providing an incentive for employees, directors and consultants of
the Company or its Affiliates;

      WHEREAS, the parties hereto understand and agree that any terms used and
not defined herein have the meanings ascribed to such terms in the Plan and that
any and all references herein to employment of the Participant by the Company
shall include the Participant's employment or service as an employee, director
or consultant of the Company or any Affiliate;

      WHEREAS, pursuant to the exercise of an option granted to the Participant
pursuant to a Non-Qualified Stock Option Agreement dated ___________ by and
between the Company and the Participant issued under the Plan (the "Option
Agreement"), which Option Agreement and Plan are hereby incorporated herein by
reference, the Participant has elected to purchase _________ shares of the
Company's common stock, $.0001 par value per share ("Common Stock"), which have
not become vested under the vesting schedule set forth in the Option Agreement
(the "Unvested Shares"). The Unvested Shares and the Shares subject to the
Option Agreement that have become vested are sometimes collectively referred to
herein as the "Shares."

      WHEREAS, as required by the Option Agreement, as a condition to the
Participant's election to exercise the option, the Participant must execute this
Agreement, which sets forth the rights and obligations of the parties with
respect to the Unvested Shares acquired upon exercise of the option pursuant to
the Option Agreement; and

      WHEREAS, Participant wishes to accept said offer in accordance with the
provisions of the Plan, all on the terms and conditions hereinafter set forth.

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

                                      C-1
<PAGE>

      1.    Company's Lapsing Repurchase Right.

      (a)   Lapsing Repurchase Right. Except as set forth in Subsection 1(b)
hereof, in the event that for any reason the Participant no longer is an
employee, director or consultant of the Company or an Affiliate, the Company (or
its designee) shall have the option, but not the obligation, to purchase from
the Participant (or the Participant's Survivor), and, in the event the Company
exercises such option, the Participant (or the Participant's Survivor) shall be
obligated to sell to the Company (or its designee), at a price per Share equal
to the Purchase Price, all or any part of the Unvested Shares determined as of
the date of such termination of service (the "Lapsing Repurchase Right"). The
Lapsing Repurchase Right with respect to the Unvested Shares shall terminate as
to such Unvested Shares in accordance with the vesting schedule set forth in
Section 3 of the Option Agreement. The Company's Lapsing Repurchase Right shall
be valid for a period of one year commencing with the date of such termination
of employment or service. Notwithstanding any other provision hereof, in the
event the Company is prohibited during such one year period from exercising its
Lapsing Repurchase Right by Section 160 of the Delaware General Corporation Law
as amended from time to time (or any successor provision), then the time period
during which such Lapsing Repurchase Right may be exercised shall be extended
until 30 days after the Company is first not so prohibited.

      (b)   Effect of Termination for Disability or upon Death. The following
rules apply if the Participant ceases to be an employee, director or consultant
of the Company by reason of Disability or death: to the extent the Company's
Lapsing Repurchase Right has not lapsed as of the date of Disability or death,
as case may be, the Company may exercise such Lapsing Repurchase Right;
provided, however, that the Company's Lapsing Repurchase Right shall be deemed
to have lapsed to the extent of a pro rata portion of the Unvested Shares
through the date of Disability or death, as would have lapsed had the
Participant not become Disabled or died, as the case may be. The proration shall
be based upon the number of days accrued in such current vesting period prior to
the Participant's date of Disability or death, as the case may be.

      (c)   Closing. In the event that the Company exercises the Lapsing
Repurchase Right, the Company shall notify the Participant, or, in the case of
the Participant's death, his or her Survivor, in writing of its intent to
repurchase the Unvested Shares. Such notice may be mailed by the Company up to
and including the last day of the time period provided for above for exercise of
the Lapsing Repurchase Right. The notice shall specify the place, time and date
for payment of the repurchase price (the "Closing") and the number of Unvested
Shares with respect to which the Company is exercising the Lapsing Repurchase
Right. The Closing shall be not less than ten days nor more than 60 days from
the date of mailing of the notice, and the Participant or the Participant's
Survivor with respect to the Unvested Shares which the Company elects to
repurchase shall have no further rights as the owner thereof from and after the
date specified in the notice. At the Closing, the repurchase price shall be
delivered to the Participant or the Participant's Survivor and the Unvested
Shares being repurchased, duly endorsed for transfer, shall, to the extent that
they are not then in the possession of the Company, be delivered to the Company
by the Participant or the Participant's Survivor.

      (d)   Escrow. The certificates representing all Unvested Shares acquired
by the Participant hereunder which from time to time are subject to the Lapsing
Repurchase

                                      C-2
<PAGE>

Right shall be delivered to the Company and the Company shall hold such Unvested
Shares in escrow as provided in this Subsection 1(d). Promptly following receipt
by the Company of a written request from the Participant, the Company shall
release from escrow and deliver to the Participant a certificate for the whole
number of Unvested Shares, if any, as to which the Company's Lapsing Repurchase
Right has lapsed. In the event of a repurchase by the Company of Unvested Shares
subject to the Lapsing Repurchase Right, the Company shall release from escrow
and cancel a certificate for the number of Unvested Shares so repurchased. Any
securities distributed in respect of the Unvested Shares held in escrow,
including, without limitation, shares issued as a result of stock splits, stock
dividends or other recapitalizations, shall also be held in escrow in the same
manner as the Unvested Shares.

      (e)   Prohibition on Transfer. The Participant recognizes and agrees that
all Unvested Shares which are subject to the Lapsing Repurchase Right may not be
sold, transferred, assigned, hypothecated, pledged, encumbered or otherwise
disposed of, whether voluntarily or by operation of law, other than to the
Company (or its designee). However, the Participant, with the approval of the
Administrator, may transfer the Unvested Shares for no consideration to or for
the benefit of the Participant's Immediate Family (including, without
limitation, to a trust for the benefit of the Participant's Immediate Family or
to a partnership or limited liability company for one or more members of the
Participant's Immediate Family), subject to such limits as the Administrator may
establish, and the transferee shall remain subject to all the terms and
conditions applicable to this Agreement prior to such transfer and each such
transferee shall so acknowledge in writing as a condition precedent to the
effectiveness of such transfer. The term "Immediate Family" shall mean the
Participant's spouse, former spouse, parents, children, stepchildren, adoptive
relationships, sisters, brothers, nieces and nephews and grandchildren (and, for
this purpose, shall also include the Participant. The Company shall not be
required to transfer any Unvested Shares on its books which shall have been
sold, assigned or otherwise transferred in violation of this Subsection 1(e), or
to treat as the owner of such Unvested Shares, or to accord the right to vote as
such owner or to pay dividends to, any person or organization to which any such
Unvested Shares shall have been so sold, assigned or otherwise transferred, in
violation of this Subsection 1(e). The Participant further recognizes and agrees
that all Shares remain subject to Section 12 of the Option Agreement, except
that with respect to the Unvested Shares subject to the Lapsing Repurchase
Right, this Agreement will supercede Section 12.3 of the Option Agreement.

      (f)   Failure to Deliver Unvested Shares to be Repurchased. In the event
that the Unvested Shares to be repurchased by the Company under this Agreement
are not in the Company's possession pursuant to Subsection 1(d) above or
otherwise and the Participant or the Participant's Survivor fails to deliver
such Unvested Shares to the Company (or its designee), the Company may elect (i)
to establish a segregated account in the amount of the repurchase price, such
account to be turned over to the Participant or the Participant's Survivor upon
delivery of such Unvested Shares, and (ii) immediately to take such action as is
appropriate to transfer record title of such Unvested Shares from the
Participant to the Company (or its designee) and to treat the Participant and
such Unvested Shares in all respects as if delivery of such Unvested Shares had
been made as required by this Agreement. The Participant hereby irrevocably
grants the Company a power of attorney

                                      C-3
<PAGE>

which shall be coupled with an interest for the purpose of effectuating the
preceding sentence.

      (g)   Adjustments. The Plan and the Option Agreement contain provisions
covering the treatment of Shares in a number of contingencies such as stock
splits and mergers. Provisions in the Plan and the Option Agreement for
adjustment with respect to the Shares and the related provisions with respect to
successors to the business of the Company are hereby made applicable hereunder
and are incorporated herein by reference.

      2.    Legend. In addition to any legend required pursuant to the Plan or
the Option Agreement, all certificates representing the Unvested Shares to be
issued to the Participant pursuant to this Agreement shall have endorsed thereon
a legend substantially as follows:

            "The shares represented by this certificate are subject to
            restrictions set forth in a Restricted Stock Agreement dated as of
            ____________, 200__ with this Company, a copy of which Agreement is
            available for inspection at the offices of the Company or will be
            made available upon request."

      3.    Purchase for Investment. If the offering and sale of the Unvested
Shares have not been effectively registered under the Securities Act of 1933, as
amended, the Participant hereby represents and warrants that he or she is
acquiring the Unvested Shares for his or her own account, for investment, and
not with a view to, or for sale in connection with, the distribution of any such
Unvested Shares.

      4.    Provisions of Agreement Controlling. The Participant specifically
understands and agrees that the Unvested Shares issued under the Plan are being
sold to the Participant pursuant to the Plan and the Option Agreement, a copy of
which Plan and Option Agreement the Participant acknowledges he or she has read
and understands and by which Plan and Option Agreement he or she agrees to be
bound. The provisions of the Plan and the Option Agreement are incorporated
herein by reference. In the event of a conflict between the terms and conditions
of the Plan, this Agreement and the Option Agreement, the provisions of this
Agreement will control.

      5.    Tax Liability of the Participant and Payment of Taxes. The
Participant acknowledges and agrees that any income or other taxes due from the
Participant with respect to the Unvested Shares issued pursuant to this
Agreement, including, without limitation, the Lapsing Repurchase Right, shall be
the Participant's responsibility. Without limiting the foregoing, the
Participant agrees that, to the extent that the lapsing of restrictions on
disposition of any of the Unvested Shares or the declaration of dividends on any
such shares before the lapse of such restrictions on disposition results in the
Participant's being deemed to be in receipt of earned income under the
provisions of the Code, the Company shall be entitled to immediate payment from
the Participant of the amount of any tax required to be withheld by the Company.

      Upon execution of this Agreement, the Participant may file an election
under Section 83 of the Code in substantially the form attached as Attachment I.
The Participant acknowledges that if she does not file such an election, as the
Unvested Shares are released

                                      C-4
<PAGE>

from the Lapsing Repurchase Right in accordance with Section 1, the Participant
will have income for tax purposes equal to the fair market value of the Unvested
Shares at such date, less the price paid for the Unvested Shares by the
Participant.

      6.    Securities Law Compliance. The Participant specifically acknowledges
and agrees that any sales of Unvested Shares shall be made in accordance with
the requirements of the Securities Act of 1933, as amended, in a transaction as
to which the Company shall have received an opinion of counsel satisfactory to
it confirming such compliance.

      7.    Equitable Relief. The Participant specifically acknowledges and
agrees that in the event of a breach or threatened breach of the provisions of
this Agreement, the Option Agreement or the Plan, including the attempted
transfer of the Unvested Shares by the Participant in violation of this
Agreement or the Option Agreement, monetary damages may not be adequate to
compensate the Company, and, therefore, in the event of such a breach or
threatened breach, in addition to any right to damages, the Company shall be
entitled to equitable relief in any court having competent jurisdiction. Nothing
herein shall be construed as prohibiting the Company from pursuing any other
remedies available to it for any such breach or threatened breach.

      8.    No Obligation to Maintain Relationship. The Company is not by the
Plan, the Option Agreement or this Agreement obligated to continue the
Participant as an employee, director or consultant of the Company. The
Participant acknowledges: (i) that the Plan is discretionary in nature and may
be suspended or terminated by the Company at any time; (ii) that the grant of
the Shares is a one-time benefit which does not create any contractual or other
right to receive future grants of shares, or benefits in lieu of shares; (iii)
that all determinations with respect to any such future grants, including, but
not limited to, the times when shares shall be granted, the number of shares to
be granted, the Purchase Price, and the time or times when each share shall be
free from the Lapsing Repurchase Right, will be at the sole discretion of the
Company; (iv) that the Participant's participation in the Plan is voluntary; (v)
that the value of the Shares is an extraordinary item of compensation which is
outside the scope of the Participant's employment contract, if any; and (vi)
that the Shares are not part of normal or expected compensation for purposes of
calculating any severance, resignation, redundancy, end of service payments,
bonuses, long-service awards, pension or retirement benefits or similar
payments.

      9.    Notices. Any notices required or permitted by the terms of this
Agreement, the Option Agreement or the Plan shall be given by recognized courier
service, facsimile, registered or certified mail, return receipt requested,
addressed as follows:

      If to the Company:

           Alnylam Holding Co.

           _______________________

           _______________________

                                      C-5
<PAGE>

      If to the Participant:

           ___________________________

           ___________________________

           ___________________________

or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given on the
earliest of receipt, one business day following delivery by the sender to a
recognized courier service, or three business days following mailing by
registered or certified mail.

      10.   Binding Effect. This Agreement shall be for the benefit of and shall
be binding upon the parties hereto, upon their respective successors and assigns
and upon the Participant's heirs, executors, administrators.

      11.   Governing Law. This Agreement shall be construed and enforced in
accordance with the laws of the State of Delaware, without giving effect to the
conflict of law principles thereof. For the purpose of litigating any dispute
that arises under this Agreement, whether at law or in equity, the parties
hereby consent to exclusive jurisdiction in Massachusetts and agree that such
litigation shall be conducted in the courts of Suffolk County, Massachusetts or
the federal courts of the United States for the District of Massachusetts.

      12.   Severability. If any provision of this Agreement is held to be
invalid or unenforceable by a court of competent jurisdiction, then such
provision or provisions shall be modified to the extent necessary to make such
provision valid and enforceable, and to the extent that this is impossible, then
such provision shall be deemed to be excised from this Agreement, and the
validity, legality and enforceability of the rest of this Agreement shall not be
affected thereby.

      13.   Entire Agreement. This Agreement, together with the Plan and the
Option Agreement, constitutes the entire agreement and understanding between the
parties hereto with respect to the subject matter hereof and supersedes all
prior oral or written agreements and understandings relating to the subject
matter hereof. No statement, representation, warranty, covenant or agreement not
expressly set forth in this Agreement, the Option Agreement or the Plan shall
affect or be used to interpret, change or restrict the express terms and
provisions of this Agreement provided, however, in any event, this Agreement
shall be subject to and governed by the Plan.

      14.   Modifications and Amendments; Waivers and Consents. The terms and
provisions of this Agreement may be modified or amended as provided in the Plan.
Except as provided in the Plan, the terms and provisions of this Agreement may
be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be

                                      C-6
<PAGE>

effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

      15.   Consent of Spouse. If the Participant is married as of the date of
this Agreement, the Participant's spouse shall execute a Consent of Spouse in
the form of Attachment II hereto, effective as of the date hereof. Such consent
shall not be deemed to confer or convey to the spouse any rights in the Unvested
Shares that do not otherwise exist by operation of law or the agreement of the
parties. If the Participant marries or remarries subsequent to the date hereof,
the Participant shall, not later than 60 days thereafter, obtain his or her new
spouse's acknowledgement of and consent to the existence and binding effect of
all restrictions contained in this Agreement by such spouse's executing and
delivering a Consent of Spouse in the form of Attachment II.

      16.   Counterparts. This Agreement may be executed in one or more
counterparts, and by different parties hereto on separate counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

      17.   Data Privacy. By entering into this Agreement, the Participant: (i)
authorizes the Company and each Affiliate, and any agent of the Company or any
Affiliate administering the Plan or providing Plan record keeping services, to
disclose to the Company or any of its Affiliates such information and data as
the Company or any such Affiliate shall request in order to facilitate the grant
of Shares and the administration of the Plan; (ii) waives any data privacy
rights he or she may have with respect to such information; and (iii) authorizes
the Company and each Affiliate to store and transmit such information in
electronic form.

                      [THE NEXT PAGE IS THE SIGNATURE PAGE]

                                      C-7
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

                                          ALNYLAM HOLDING CO.

                                          By:___________________________________
                                          Name:
                                          Title:

                                          PARTICIPANT:

                                          ______________________________________
                                          Print name:

                                      C-8
<PAGE>

                                                                    ATTACHMENT I

                    ELECTION TO INCLUDE GROSS INCOME IN YEAR
                      OF TRANSFER PURSUANT TO SECTION 83(b)
                OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED

      In accordance with Section 83(b) of the Internal Revenue Code of 1986, as
amended (the "Code"), the undersigned hereby elects to include in his gross
income as compensation for services the excess, if any, of the fair market value
of the property (described below) at the time of transfer over the amount paid
for such property.

The following sets for the information required in accordance with the Code and
the regulations promulgated hereunder:

1.    The name, address and social security number of the undersigned are:

           Name:
           Address:
           Social Security No.:

2.    The description of the property with respect to which the election is
      being made is as follows:

      ____________ (___) shares (the "Shares") of Common Stock, $.0001 par value
      per share, of Alnylam Holding Co., a Delaware corporation (the "Company").

3.    This election is made for the calendar year ____, with respect to the
      transfer of the property to the Taxpayer on _________________.

4.    Description of restrictions: The property is subject to the following
      restrictions:

      In the event taxpayer's employment with the Company or an Affiliate is
      terminated, the Company may repurchase all or any portion of the Shares
      determined as set forth below at the acquisition price paid by the
      taxpayer:

      A.    If the termination takes place on or prior to ____________, the
            Purchase Option will apply to all of the Shares.

      B.    If the termination takes place after __________, 200_, the number of
            Shares to which the Purchase Option applies shall be ______________
            (___) Shares less (i)_______________ (___) Shares and (ii)
            ___________________ (___) Shares for each period ending each _____,
            _____, _____ and _____  elapsed after _____________, 200_ if the
            taxpayer is employed by the Company or an Affiliate.

                                      I-1
<PAGE>

5.    The fair market value at time of transfer (determined without regard to
      any restrictions other than restrictions which by their terms will never
      lapse) of the property with respect to which this election is being made
      was not more than $____ per Share.

6.    The amount paid by taxpayer for said property was $___ per Share.

7.    A copy of this statement has been furnished to the Company.

Signed this ____ day of ______, 200_.

                                                ________________________________
                                                Print Name:

                                      I-2
<PAGE>

                                                                   ATTACHMENT II

                                CONSENT OF SPOUSE

      I, ____________________________, spouse of _____________________________,
acknowledge that I have read the RESTRICTED STOCK AGREEMENT dated as of
_______________, 200__ (the "Agreement") to which this Consent is attached as
Attachment II and that I know its contents. Capitalized terms used and not
defined herein shall have the meanings assigned to such terms in the Agreement.
I am aware that by its provisions the Unvested Shares granted to my spouse
pursuant to the Agreement are subject to a Lapsing Repurchase Right in favor of
Alnylam Holding Co. (the "Company") and that, accordingly, the Company has the
right to repurchase up to all of the Unvested Shares of which I may become
possessed as a result of a gift from my spouse or a court decree and/or any
property settlement in any domestic litigation.

      I hereby agree that my interest, if any, in the Unvested Shares subject to
the Agreement shall be irrevocably bound by the Agreement and further understand
and agree that any community property interest I may have in the Unvested Shares
shall be similarly bound by the Agreement.

      I agree to the Lapsing Repurchase Right described in the Agreement and I
hereby consent to the repurchase of the Unvested Shares by the Company and the
sale of the Unvested Shares by my spouse or my spouse's legal representative in
accordance with the provisions of the Agreement. Further, as part of the
consideration for the Agreement, I agree that at my death, if I have not
disposed of any interest of mine in the Unvested Shares by an outright bequest
of the Unvested Shares to my spouse, then the Company shall have the same rights
against my legal representative to exercise its rights of repurchase with
respect to any interest of mine in the Unvested Shares as it would have had
pursuant to the Agreement if I had acquired the Unvested Shares pursuant to a
court decree in domestic litigation.

      I AM AWARE THAT THE LEGAL, FINANCIAL AND RELATED MATTERS CONTAINED IN THE
AGREEMENT ARE COMPLEX AND THAT I AM FREE TO SEEK INDEPENDENT PROFESSIONAL
GUIDANCE OR COUNSEL WITH RESPECT TO THIS CONSENT. I HAVE EITHER SOUGHT SUCH
GUIDANCE OR COUNSEL OR DETERMINED AFTER REVIEWING THE AGREEMENT CAREFULLY THAT I
WILL WAIVE SUCH RIGHT.

      Dated as of the _______ day of ________________, 200__.

                                                ________________________________
                                                Print name:

                                      II-1
<PAGE>

                           RESTRICTED STOCK AGREEMENT

                               ALNYLAM HOLDING CO.

      AGREEMENT made as of the ___ day of ____________, 200__ (the "Grant
Date"), between Alnylam Holding Co. (the "Company"), a Delaware corporation
having its principal place of business in Cambridge, Massachusetts, and
________________ of ________________________, (the "Participant").

      WHEREAS, the Company has adopted the Alnylam Holding Co. 2003 Employee,
Director and Consultant Stock Plan (the "Plan") to promote the interests of the
Company by providing an incentive for employees, directors and consultants of
the Company or its Affiliates;

      WHEREAS, pursuant to the provisions of the Plan, the Company desires to
offer for sale to the Participant shares of the Company's common stock, $.0001
par value per share ("Common Stock"), in accordance with the provisions of the
Plan, all on the terms and conditions hereinafter set forth;

      WHEREAS, Participant wishes to accept said offer; and

      WHEREAS, the parties hereto understand and agree that any terms used and
not defined herein have the meanings ascribed to such terms in the Plan.

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

      1.    Terms of Purchase. The Participant hereby accepts the offer of the
Company to issue to the Participant, in accordance with the terms of the Plan
and this Agreement, _______________________ Shares of the Company's Common Stock
(such shares, subject to adjustment pursuant to Section 23 of the Plan and
Subsection 2.1(i) hereof, the "Granted Shares") at a purchase price per share of
$______ (the "Purchase Price"), receipt of which is hereby acknowledged by the
Company. Payment shall be made in accordance with Section 9 of the Plan.

      2.1.  Company's Lapsing Repurchase Right.

      (a)   Lapsing Repurchase Right. Except as set forth in Subsections 2.1(b)
hereof, in the event that for any reason the Participant no longer is an
employee, director or consultant of the Company or an Affiliate prior to the
fourth anniversary of the Grant Date, the Company (or its designee) shall have
the option, but not the obligation, to purchase from the Participant (or the
Participant's Survivor), and, in the event the Company exercises such option,
the Participant (or the Participant's Survivor) shall be obligated to sell to
the Company (or its designee), at a price per Granted Share equal to the
Purchase Price, all or any part of the Granted Shares set forth in clauses (i),
(ii) and (iii) below (the "Lapsing Repurchase Right"). The Company's Lapsing

<PAGE>

Repurchase Right shall be valid for a period of one year commencing with the
date of such termination of employment or service. Notwithstanding any other
provision hereof, in the event the Company is prohibited during such one year
period from exercising its Lapsing Repurchase Right by Section 160 of the
Delaware General Corporation Law as amended from time to time (or any successor
provision), then the time period during which such Lapsing Repurchase Right may
be exercised shall be extended until 30 days after the Company is first not so
prohibited.

            (i)   If such termination is prior to the first anniversary of the
      Grant Date, the Company shall have the option to repurchase all of the
      Granted Shares acquired by the Participant hereunder.

            (ii)  If such termination is on or after the first anniversary of
      the Grant Date, the Company shall have the option to repurchase all of the
      Granted Shares less ___________ of the Granted Shares and an additional
      ___________ for each period ending on each _____, _____, _____ and _____
      after the first anniversary of the Grant Date that the Participant
      continues to serve as an employee, director or consultant of the Company
      or an Affiliate.

            (iii) Notwithstanding anything to the contrary contained in this
      Agreement, in the event the Company or an Affiliate terminates the
      Participant's employment or service for "cause" (as defined in the Plan)
      or in the event the Administrator determines, within 90 days after the
      Participant's termination, that either prior or subsequent to the
      Participant's termination the Participant engaged in conduct that would
      constitute "cause," the Company shall have the option to repurchase all of
      the Granted Shares acquired by the Participant hereunder at the Purchase
      Price.

      (b)   Effect of Termination for Disability or upon Death. Except as
otherwise provided in Subsection 2.1(a)(iii) above, the following rules apply if
the Participant ceases to be an employee, director or consultant of the Company
or an Affiliate by reason of Disability or death: to the extent the Company's
Lapsing Repurchase Right has not lapsed as of the date of Disability or death,
as case may be, the Company may exercise such Lapsing Repurchase Right;
provided, however, that the Company's Lapsing Repurchase Right shall be deemed
to have lapsed to the extent of a pro rata portion of the Granted Shares through
the date of Disability or death, as would have lapsed had the Participant not
become Disabled or died, as the case may be. The proration shall be based upon
the number of days accrued in such current vesting period prior to the
Participant's date of Disability or death, as the case may be.

      (c)   Closing. In the event that the Company exercises the Lapsing
Repurchase Right, the Company shall notify the Participant, or, in the case of
the Participant's death, his or her Survivor, in writing of its intent to
repurchase the Granted Shares. Such notice may be mailed by the Company up to
and including the last day of the time period provided for above for exercise of
the Lapsing Repurchase Right. The notice shall specify the place, time and date
for payment of the repurchase price (the "Closing") and the number of Granted
Shares with respect to which the Company is exercising the Lapsing Repurchase
Right. The Closing shall be not less

                                       2
<PAGE>

than ten days nor more than 60 days from the date of mailing of the notice, and
the Participant or the Participant's Survivor with respect to the Granted Shares
which the Company elects to repurchase shall have no further rights as the owner
thereof from and after the date specified in the notice. At the Closing, the
repurchase price shall be delivered to the Participant or the Participant's
Survivor and the Granted Shares being repurchased, duly endorsed for transfer,
shall, to the extent that they are not then in the possession of the Company, be
delivered to the Company by the Participant or the Participant's Survivor.

      (d)   Escrow. The certificates representing all Granted Shares acquired by
the Participant hereunder which from time to time are subject to the Lapsing
Repurchase Right shall be delivered to the Company and the Company shall hold
such Granted Shares in escrow as provided in this Subsection 2.1(d). Promptly
following receipt by the Company of a written request from the Participant, the
Company shall release from escrow and deliver to the Participant a certificate
for the whole number of Granted Shares, if any, as to which the Company's
Lapsing Repurchase Right has lapsed. In the event of a repurchase by the Company
of Granted Shares subject to the Lapsing Repurchase Right, the Company shall
release from escrow and cancel a certificate for the number of Granted Shares so
repurchased. Any securities distributed in respect of the Granted Shares held in
escrow, including, without limitation, shares issued as a result of stock
splits, stock dividends or other recapitalizations, shall also be held in escrow
in the same manner as the Granted Shares.

      (e)   Prohibition on Transfer. The Participant recognizes and agrees that
all Granted Shares which are subject to the Lapsing Repurchase Right may not be
sold, transferred, assigned, hypothecated, pledged, encumbered or otherwise
disposed of, whether voluntarily or by operation of law, other than to the
Company (or its designee). However, the Participant, with the approval of the
Administrator, may transfer the Granted Shares for no consideration to or for
the benefit of the Participant's Immediate Family (including, without
limitation, to a trust for the benefit of the Participant's Immediate Family or
to a partnership or limited liability company for one or more members of the
Participant's Immediate Family), subject to such limits as the Administrator may
establish, and the transferee shall remain subject to all the terms and
conditions applicable to this Agreement prior to such transfer and each such
transferee shall so acknowledge in writing as a condition precedent to the
effectiveness of such transfer. The term "Immediate Family" shall mean the
Participant's spouse, former spouse, parents, children, stepchildren, adoptive
relationships, sisters, brothers, nieces and nephews and grandchildren (and, for
this purpose, shall also include the Participant. The Company shall not be
required to transfer any Granted Shares on its books which shall have been sold,
assigned or otherwise transferred in violation of this Subsection 2.1(e), or to
treat as the owner of such Granted Shares, or to accord the right to vote as
such owner or to pay dividends to, any person or organization to which any such
Granted Shares shall have been so sold, assigned or otherwise transferred, in
violation of this Subsection 2.1(e).

      (f)   Failure to Deliver Granted Shares to be Repurchased. In the event
that the Granted Shares to be repurchased by the Company under this Agreement
are not in the Company's possession pursuant to Subsection 2.1(d) above or
otherwise and the Participant or the Participant's Survivor fails to deliver
such Granted Shares to the Company (or its designee), the Company may elect (i)
to establish a segregated account in the amount of the repurchase

                                       3
<PAGE>

price, such account to be turned over to the Participant or the Participant's
Survivor upon delivery of such Granted Shares, and (ii) immediately to take such
action as is appropriate to transfer record title of such Granted Shares from
the Participant to the Company (or its designee) and to treat the Participant
and such Granted Shares in all respects as if delivery of such Granted Shares
had been made as required by this Agreement. The Participant hereby irrevocably
grants the Company a power of attorney which shall be coupled with an interest
for the purpose of effectuating the preceding sentence.

      (g)   Adjustments. The Plan contains provisions covering the treatment of
Shares in a number of contingencies such as stock splits and mergers. Provisions
in the Plan for adjustment with respect to the Shares and the related provisions
with respect to successors to the business of the Company are hereby made
applicable hereunder and are incorporated herein by reference, provided,
however, in the event of a Change of Control (as defined in the Plan) which the
Administrator (as defined in the Plan) or the Successor Board (as defined in the
Plan) makes provisions for the treatment of Stock Grants under (A) clause (i) of
the second paragraph of Section 23(B) of the Plan, an additional one-sixteenth
(1/16) of the Shares shall become fully vested and the Company's Lapsing
Repurchase Right shall terminate as to such additional one-sixteenth (1/16) of
the Shares immediately prior to such Change of Control and the remaining
unvested Shares shall vest in accordance with the provisions of this Agreement,
provided, however, if the Participant's employment with the Company is
Terminated (as defined below), fifty percent (50%) of all unvested Shares shall
become fully vested and the Company's Lapsing Repurchase Right shall terminate
with respect to such fifty percent (50%) of the Shares immediately prior to such
termination (for purposes of this Section 2.1(g), the Participant shall be
deemed to have been "Terminated" if at any time before the six-month anniversary
of the closing of such Change of Control, (i) the Employee shall fail to be
vested with power and authority analogous to the Participant's title and/or
office prior to such Change of Control, (ii) the Participant shall lose any
significant duties or responsibilities attending such office, (iii) there shall
occur a reduction in the Participant's base compensation, or (iv) the
Participant's employment with the Company or an Affiliate, or its successor is
terminated without "cause" (as defined in the Plan)) or (B) either clause (ii)
or (iii) of the second paragraph of Section 23(B) of the Plan, all Shares shall
become fully vested immediately prior to such Change of Control and the
Company's Lapsing Repurchase Right shall terminate immediately prior to such
Change of Control.

      2.2   General Restrictions on Transfer of Granted Shares.

      (a)   Limitations on Transfer. In addition to the restrictions set forth
above in Section 2.1, the Granted Shares acquired by the Participant hereunder
and no longer subject to the provisions of Section 2.1 herein (the "Vested
Shares") shall not be transferred by the Participant except as permitted herein,
shall be subject to the provisions of Sections 2.1 (d), (e) and (f) above and
shall be subject to the repurchase rights described herein.

      (b)   Right to Repurchase following Termination of Service. If the
Participant's service as an employee, director or consultant with the Company or
an Affiliate shall be terminated for any reason other than for "cause" (as
defined in the Plan), including due to death or Disability, then the Company
shall have the option to repurchase the Vested Shares not

                                       4
<PAGE>

previously repurchased in accordance with the provisions of Section 2.1 of this
Agreement as follows:

                  (i)   The Company's option to repurchase the Vested Shares in
            the event of termination of service under this Section 2.2(b) shall
            be valid for a period of one year commencing with the date of such
            termination of service.

                  (ii)  In the event the Company shall be entitled to and shall
            elect to exercise its option to repurchase the Vested Shares under
            this Section 2.2(b), the Company shall notify the Participant, or in
            case of death, his or her Survivor, in writing of its intent to
            repurchase the Vested Shares. Such written notice may be mailed by
            the Company up to and including the last day of the time period
            provided for in Section 2.2(b)(i) for exercise of the Company's
            option to repurchase.

                  (iii) The written notice to the Participant shall specify the
            address at, and the time and date on, which payment of the
            Repurchase Price (as defined herein) is to be made (the "Closing").
            The date specified shall not be less than ten days nor more than 60
            days from the date of the mailing of the notice, and the Participant
            or the Participant's Survivor with respect to the Vested Shares
            shall have no further rights as the owner thereof from and after the
            date specified in the notice. At the Closing, the Repurchase Price
            (as defined below) shall be delivered to the Participant or the
            Participant's Survivor and the Vested Shares being purchased, duly
            endorsed for transfer, shall, to the extent that they are not then
            in the possession of the Company, be delivered to the Company by the
            Participant or the Participant's Survivor.

                  (iv)  The price paid per share for any Vested Shares
            repurchased hereunder (the "Repurchase Price") shall equal the Fair
            Market Value of such Vested Shares determined in accordance with the
            Plan as of the date of termination of service, provided, however, in
            the event of a termination by the Company or an Affiliate for
            "cause" (as defined in the Plan), the per share repurchase price of
            the Shares to be sold to the Company upon exercise of its option
            under this Section 12.2 shall be equal to the Purchase Price.

      (c)   Right to Repurchase on Proposed Transfer. It shall be a condition
precedent to the validity of any sale or other transfer of any Vested Shares by
the Participant that the following restrictions be complied with (except as
hereinafter otherwise provided):

            (i)   No Vested Shares owned by the Participant may be sold, pledged
      or otherwise transferred (including by gift or devise) to any person or
      entity, voluntarily, or by operation of law, except in accordance with the
      terms and conditions hereinafter set forth.

            (ii)  Before selling or otherwise transferring all or part of the
      Vested Shares, the Participant shall give written notice of such intention
      to the Company which notice

                                       5
<PAGE>

      shall include the name of the proposed transferee, the proposed purchase
      price per share, the terms of payment of such purchase price and all other
      matters relating to such sale or transfer and shall be accompanied by a
      copy of the binding written agreement of the proposed transferee to
      purchase the Vested Shares of the Participant. Such notice shall
      constitute a binding offer by the Participant to sell to the Company such
      number of the Vested Shares then held by the Participant as are proposed
      to be sold in the notice at the monetary price per share designated in
      such notice, payable on the terms offered to the Participant by the
      proposed transferee (provided, however, that the Company shall not be
      required to meet any non-monetary terms of the proposed transfer,
      including, without limitation, delivery of other securities in exchange
      for the Vested Shares proposed to be sold). The Company shall give written
      notice to the Participant as to whether such offer has been accepted in
      whole by the Company within 60 days after its receipt of written notice
      from the Participant. The Company may only accept such offer in whole and
      may not accept such offer in part. Such acceptance notice shall specify a
      place, a time, and date for the closing on such purchase (the "Closing")
      which shall not be less than ten nor more than 60 days after the giving of
      the acceptance notice. At the Closing, the Participant shall accept
      payment as set forth herein and shall deliver to the Company in exchange
      therefor the Granted Shares being repurchased, duly endorsed for transfer,
      to the extent that they are not then in the possession of the Company.

            (iii) If the Company shall fail to accept any such offer, the
      Participant shall be free to sell all, but not less than all, of the
      Vested Shares set forth in her notice to the designated transferee at the
      price and terms designated in the Participant's notice, provided that (i)
      such sale is consummated within six months after the giving of notice by
      the Participant to the Company as aforesaid, and (ii) the transferee first
      agrees in writing to be bound by the provisions of this Section 2.2(c) so
      that he or she (and all subsequent transferees) shall thereafter only be
      permitted to sell or transfer the Vested Shares in accordance with the
      terms hereof. After the expiration of such six months, the provisions of
      this Section 2.2(c) shall again apply with respect to any proposed
      voluntary transfer of the Vested Shares.

            (iv)  The provisions of this Section 2.2(c) may be waived by the
      Company. Any such waiver may be unconditional or based upon such
      conditions as the Company may impose.

            (v)   The restrictions on transfer contained in this Section 2.2(c)
      shall not apply to (a) transfers by the Participant to his or her spouse
      or children or to a trust for the benefit of his or her spouse or
      children, (b) transfers by the Participant to his or her guardian or
      conservator, and (c) or transfers by the Participant, in the event of his
      or her death, to his or her executor(s) or administrator(s) or to
      trustee(s) under his or her will (collectively, "Permitted Transferees");
      provided however, that in any such event the Vested Shares so transferred
      in the hands of each such Permitted Transferee shall remain subject to
      this Agreement, and each such Permitted Transferee shall so acknowledge in
      writing as a condition precedent to the effectiveness of such transfer.

                                       6
<PAGE>

      (d)   The provisions of Section 2.2 (a) through (d) shall terminate upon
the consummation of a public offering of any of the Company's securities
pursuant to a registration statement filed with the Securities and Exchange
Commission pursuant to the Securities Act of 1933, as amended (the "1933 Act").

      (e)   If in connection with a registration statement filed by the Company
pursuant to the 1933 Act, the Company or its underwriter so requests, the
Participant will agree not to sell any of her Vested Shares for a period not to
exceed the lesser of: (i) 180 days following the effectiveness of such
registration statement or (ii) such period as the officers and directors of the
Company agree not to sell their Common Stock of the Company.

      (f)   The Participant acknowledges and agrees that neither the Company
nor, its shareholders nor its directors and officers, has any duty or obligation
to disclose to the Participant any material information regarding the business
of the Company or affecting the value of the Shares before, at the time of, or
following a termination of the employment of the Participant by the Company or
an Affiliate, including, without limitation, any information concerning plans
for the Company to make a public offering of its securities or to be acquired by
or merged with or into another firm or entity.

      3.    Legend. In addition to any legend required pursuant to the Plan, all
certificates representing the Granted Shares to be issued to the Participant
pursuant to this Agreement shall have endorsed thereon a legend substantially as
follows:

            "The shares represented by this certificate are subject to
            restrictions set forth in a Restricted Stock Agreement dated as of
            ____________, 200__ with this Company, a copy of which Agreement is
            available for inspection at the offices of the Company or will be
            made available upon request."

      4.    Purchase for Investment; Securities Law Compliance. If the offering
and sale of the Granted Shares have not been effectively registered under the
1933 Act, the Participant hereby represents and warrants that he or she is
acquiring the Granted Shares for his or her own account, for investment, and not
with a view to, or for sale in connection with, the distribution of any such
Granted Shares. The Participant specifically acknowledges and agrees that any
sales of Granted Shares shall be made in accordance with the requirements of the
1933 Act, in a transaction as to which the Company shall have received an
opinion of counsel satisfactory to it confirming such compliance. The
Participant shall be bound by the provisions of the following legend which shall
be endorsed upon the certificate(s) evidencing the Shares issued:

                  "The shares represented by this certificate have been taken
                  for investment and they may not be sold or otherwise
                  transferred by any person, including a pledgee, unless (1)
                  either (a) a Registration Statement with respect to such
                  shares shall be effective under the Securities Act of 1933, as
                  amended, or (b) the Company shall have received an opinion of
                  counsel satisfactory to it that an exemption from registration
                  under such Act is then available, and (2) there shall have
                  been compliance with all applicable state securities laws."

                                       7
<PAGE>

      5.    Incorporation of the Plan. The Participant specifically understands
and agrees that the Granted Shares issued under the Plan are being sold to the
Participant pursuant to the Plan, a copy of which Plan the Participant
acknowledges he or she has read and understands and by which Plan he or she
agrees to be bound. The provisions of the Plan are incorporated herein by
reference.

      6.    Tax Liability of the Participant and Payment of Taxes. The
Participant acknowledges and agrees that any income or other taxes due from the
Participant with respect to the Granted Shares issued pursuant to this
Agreement, including, without limitation, the Lapsing Repurchase Right, shall be
the Participant's responsibility. Without limiting the foregoing, the
Participant agrees that, to the extent that the lapsing of restrictions on
disposition of any of the Granted Shares or the declaration of dividends on any
such shares before the lapse of such restrictions on disposition results in the
Participant's being deemed to be in receipt of earned income under the
provisions of the Code, the Company shall be entitled to immediate payment from
the Participant of the amount of any tax required to be withheld by the Company.

      Upon execution of this Agreement, the Participant may file an election
under Section 83 of the Code in substantially the form attached as Exhibit B.
The Participant acknowledges that if she does not file such an election, as the
Granted Shares are released from the Lapsing Repurchase Right in accordance with
Section 2.1, the Participant will have income for tax purposes equal to the fair
market value of the Granted Shares at such date, less the price paid for the
Granted Shares by the Participant.

      7.    Equitable Relief. The Participant specifically acknowledges and
agrees that in the event of a breach or threatened breach of the provisions of
this Agreement or the Plan, including the attempted transfer of the Granted
Shares by the Participant in violation of this Agreement, monetary damages may
not be adequate to compensate the Company, and, therefore, in the event of such
a breach or threatened breach, in addition to any right to damages, the Company
shall be entitled to equitable relief in any court having competent
jurisdiction. Nothing herein shall be construed as prohibiting the Company from
pursuing any other remedies available to it for any such breach or threatened
breach.

      8.    No Obligation to Maintain Relationship. The Company is not by the
Plan or this Agreement obligated to continue the Participant as an employee,
director or consultant of the Company or an Affiliate. The Participant
acknowledges: (i) that the Plan is discretionary in nature and may be suspended
or terminated by the Company at any time; (ii) that the grant of the Shares is a
one-time benefit which does not create any contractual or other right to receive
future grants of shares, or benefits in lieu of shares; (iii) that all
determinations with respect to any such future grants, including, but not
limited to, the times when shares shall be granted, the number of shares to be
granted, the purchase price, and the time or times when each share shall be free
from a lapsing repurchase right, will be at the sole discretion of the Company;
(iv) that the Participant's participation in the Plan is voluntary; (v) that the
value of the Shares is an extraordinary item of compensation which is outside
the scope of the Participant's employment contract, if any; and (vi) that the
Shares are not part of normal or expected compensation for

                                       8
<PAGE>

purposes of calculating any severance, resignation, redundancy, end of service
payments, bonuses, long-service awards, pension or retirement benefits or
similar payments.

      9.    Notices. Any notices required or permitted by the terms of this
Agreement or the Plan shall be given by recognized courier service, facsimile,
registered or certified mail, return receipt requested, addressed as follows:

      If to the Company:

         Alnylam Holding Co.

         _________________________

         _________________________


      If to the Participant:

         _____________________

         _____________________

         _____________________

or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given on the
earliest of receipt, one business day following delivery by the sender to a
recognized courier service, or three business days following mailing by
registered or certified mail.

      10.   Benefit of Agreement. Subject to the provisions of the Plan and the
other provisions hereof, this Agreement shall be for the benefit of and shall be
binding upon the heirs, executors, administrators, successors and assigns of the
parties hereto.

      11.   Governing Law. This Agreement shall be construed and enforced in
accordance with the laws of the State of Delaware, without giving effect to the
conflict of law principles thereof. For the purpose of litigating any dispute
that arises under this Agreement, whether at law or in equity, the parties
hereby consent to exclusive jurisdiction in Massachusetts and agree that such
litigation shall be conducted in the courts of Suffolk County, Massachusetts or
the federal courts of the United States for the District of Massachusetts.

      12.   Severability. If any provision of this Agreement is held to be
invalid or unenforceable by a court of competent jurisdiction, then such
provision or provisions shall be modified to the extent necessary to make such
provision valid and enforceable, and to the extent that this is impossible, then
such provision shall be deemed to be excised from this Agreement, and the
validity, legality and enforceability of the rest of this Agreement shall not be
affected thereby.

      13.   Entire Agreement. This Agreement, together with the Plan,
constitutes the entire agreement and understanding between the parties hereto
with respect to the subject matter hereof and supersedes all prior oral or
written agreements and understandings relating to the subject matter hereof. No
statement, representation, warranty, covenant or agreement not expressly set

                                       9
<PAGE>

forth in this Agreement shall affect or be used to interpret, change or restrict
the express terms and provisions of this Agreement provided, however, in any
event, this Agreement shall be subject to and governed by the Plan.

      14.   Modifications and Amendments; Waivers and Consents. The terms and
provisions of this Agreement may be modified or amended as provided in the Plan.
Except as provided in the Plan, the terms and provisions of this Agreement may
be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be
effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

      15.   Consent of Spouse. If the Participant is married as of the date of
this Agreement, the Participant's spouse shall execute a Consent of Spouse in
the form of Exhibit A hereto, effective as of the date hereof. Such consent
shall not be deemed to confer or convey to the spouse any rights in the Granted
Shares that do not otherwise exist by operation of law or the agreement of the
parties. If the Participant marries or remarries subsequent to the date hereof,
the Participant shall, not later than 60 days thereafter, obtain his or her new
spouse's acknowledgement of and consent to the existence and binding effect of
all restrictions contained in this Agreement by such spouse's executing and
delivering a Consent of Spouse in the form of Exhibit A.

      16.   Counterparts. This Agreement may be executed in one or more
counterparts, and by different parties hereto on separate counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

      17.   Data Privacy. By entering into this Agreement, the Participant: (i)
authorizes the Company and each Affiliate, and any agent of the Company or any
Affiliate administering the Plan or providing Plan record keeping services, to
disclose to the Company or any of its Affiliates such information and data as
the Company or any such Affiliate shall request in order to facilitate the grant
of Shares and the administration of the Plan; (ii) waives any data privacy
rights he or she may have with respect to such information; and (iii) authorizes
the Company and each Affiliate to store and transmit such information in
electronic form.

                      [THE NEXT PAGE IS THE SIGNATURE PAGE]

                                       10
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

                                            ALNYLAM HOLDING CO.

                                            By:_________________________________
                                            Name:
                                            Title:

                                            PARTICIPANT:

                                            ____________________________________
                                            Print name:

                                       11
<PAGE>

                                                                       EXHIBIT A

                                CONSENT OF SPOUSE

      I, ____________________________, spouse of _____________________________,
acknowledge that I have read the RESTRICTED STOCK AGREEMENT dated as of
_______________, 200__ (the "Agreement") to which this Consent is attached as
Exhibit A and that I know its contents. Capitalized terms used and not defined
herein shall have the meanings assigned to such terms in the Agreement. I am
aware that by its provisions the Granted Shares granted to my spouse pursuant to
the Agreement are subject to a Lapsing Repurchase Right in favor of Alnylam
Holding Co. (the "Company") and that, accordingly, the Company has the right to
repurchase up to all of the Granted Shares of which I may become possessed as a
result of a gift from my spouse or a court decree and/or any property settlement
in any domestic litigation.

      I hereby agree that my interest, if any, in the Granted Shares subject to
the Agreement shall be irrevocably bound by the Agreement and further understand
and agree that any community property interest I may have in the Granted Shares
shall be similarly bound by the Agreement.

      I agree to the Lapsing Repurchase Right described in the Agreement and I
hereby consent to the repurchase of the Granted Shares by the Company and the
sale of the Granted Shares by my spouse or my spouse's legal representative in
accordance with the provisions of the Agreement. Further, as part of the
consideration for the Agreement, I agree that at my death, if I have not
disposed of any interest of mine in the Granted Shares by an outright bequest of
the Granted Shares to my spouse, then the Company shall have the same rights
against my legal representative to exercise its rights of repurchase with
respect to any interest of mine in the Granted Shares as it would have had
pursuant to the Agreement if I had acquired the Granted Shares pursuant to a
court decree in domestic litigation.

      I AM AWARE THAT THE LEGAL, FINANCIAL AND RELATED MATTERS CONTAINED IN THE
AGREEMENT ARE COMPLEX AND THAT I AM FREE TO SEEK INDEPENDENT PROFESSIONAL
GUIDANCE OR COUNSEL WITH RESPECT TO THIS CONSENT. I HAVE EITHER SOUGHT SUCH
GUIDANCE OR COUNSEL OR DETERMINED AFTER REVIEWING THE AGREEMENT CAREFULLY THAT I
WILL WAIVE SUCH RIGHT.

      Dated as of the _______ day of ________________, 200__.

                                                     ___________________________
                                                     Print name:

                                      A-1
<PAGE>

                                                                       EXHIBIT B

                    ELECTION TO INCLUDE GROSS INCOME IN YEAR
                      OF TRANSFER PURSUANT TO SECTION 83(b)
                OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED

      In accordance with Section 83(b) of the Internal Revenue Code of 1986, as
amended (the "Code"), the undersigned hereby elects to include in his gross
income as compensation for services the excess, if any, of the fair market value
of the property (described below) at the time of transfer over the amount paid
for such property.

The following sets for the information required in accordance with the Code and
the regulations promulgated hereunder:

1.    The name, address and social security number of the undersigned are:

           Name:
           Address:
           Social Security No.:

2.    The description of the property with respect to which the election is
      being made is as follows:

      ____________ (___) shares (the "Shares") of Common Stock, $.0001 par value
      per share, of Alnylam Holding Co, a Delaware corporation (the "Company").

3.    This election is made for the calendar year ____, with respect to the
      transfer of the property to the Taxpayer on _________________.

4.    Description of restrictions: The property is subject to the following
      restrictions:

      In the event taxpayer's employment with the Company or an Affiliate is
      terminated, the Company may repurchase all or any portion of the Shares
      determined as set forth below at the acquisition price paid by the
      taxpayer:

      A.    If the termination takes place on or prior to ____________, the
            Purchase Option will apply to all of the Shares.

      B.    If the termination takes place after __________, 200_, the number of
            Shares to which the Purchase Option applies shall be ______________
            (___) Shares less (i)______________________(___) Shares and (ii)
            ______________ (___) Shares for each period ending each _____,
            _____, _____ and _____ elapsed after _____________, 200_ if the
            taxpayer is employed by the Company or an Affiliate.

                                      B-1
<PAGE>

5.    The fair market value at time of transfer (determined without regard to
      any restrictions other than restrictions which by their terms will never
      lapse) of the property with respect to which this election is being made
      was not more than $____ per Share.

6.    The amount paid by taxpayer for said property was $___ per Share.

7.    A copy of this statement has been furnished to the Company.

Signed this ____ day of ______, 200_.

                                                  ______________________________
                                                  Print Name:

                                      B-2