<PAGE>

                           ROSETTA INPHARMATICS, INC.

                       2000 EMPLOYEE STOCK PURCHASE PLAN

         The following constitute the provisions of the 2000 Employee Stock
Purchase Plan of Rosetta Inpharmatics, Inc.

         1.  PURPOSE.  The purpose of the Plan is to provide employees of the
Company and its Designated Subsidiaries with an opportunity to purchase
Common Stock of the Company. It is the intention of the Company to have the
Plan qualify as an "Employee Stock Purchase Plan" under Section 423 of the
Code. The provisions of the Plan shall, accordingly, be construed so as to
extend and limit participation in a manner consistent with the requirements
of that section of the Code.

         2.  DEFINITIONS.

             (a)  "BOARD" means the Board of Directors of the Company.

             (b)  "CODE" means the Internal Revenue Code of 1986, as amended.

             (c)  "COMMON STOCK" means the Common Stock of the Company.

             (d)  "COMPANY" means Rosetta Inpharmatics, Inc., a Delaware
corporation.

             (e)  "COMPENSATION" means regular straight time gross earnings,
and shall not include commissions, payments for overtime, shift premium,
incentive compensation, incentive payments, bonuses and other compensation.

             (f)  "CONTINUOUS STATUS AS AN EMPLOYEE" means the absence of any
interruption or termination of service as an Employee. Continuous Status as
an Employee shall not be considered interrupted in the case of (i) sick
leave; (ii) military leave; (iii) any other leave of absence approved by the
Administrator, provided that such leave is for a period of not more than 90
days, unless reemployment upon the expiration of such leave is guaranteed by
contract or statute, or unless provided otherwise pursuant to Company policy
adopted from time to time; or (iv) in the case of transfers between locations
of the Company or between the Company and its Designated Subsidiaries.

             (g)  "CONTRIBUTIONS" means all amounts credited to the account
of a participant pursuant to the Plan.

             (h)  "CORPORATE TRANSACTION" means a sale of all or
substantially all of the Company's assets, or a merger, consolidation or
other capital reorganization of the Company with or into another corporation.

             (i)  "DESIGNATED SUBSIDIARIES" means the Subsidiaries which have
been designated by the Board from time to time in its sole discretion as
eligible to participate in the Plan; provided however that the Board shall
only have the discretion to designate Subsidiaries if

                                      -1-
<PAGE>

the issuance of options to such Subsidiary's Employees pursuant to the Plan
would not cause the Company to incur adverse accounting charges.

             (j)  "EMPLOYEE" means any person, including an Officer, who is
customarily employed for at least twenty (20) hours per week and more than
five (5) months in a calendar year by the Company or one of its Designated
Subsidiaries.

             (k)  "EXCHANGE ACT" means the Securities Exchange Act of 1934,
as amended.

             (l)  "OFFERING DATE" means the first business day of each
Offering Period of the Plan.

             (m)  "OFFERING PERIOD" means a period of twenty-four (24) months
commencing on February 1 and August 1 of each year, except for the first
Offering Period as set forth in Section 4(a).

             (n)  "OFFICER" means a person who is an officer of the Company
within the meaning of Section 16 of the Exchange Act and the rules and
regulations promulgated thereunder.

             (o)  "PLAN" means this Employee Stock Purchase Plan.

             (p)  "PURCHASE DATE" means the last day of each Purchase Period
of the Plan.

             (q)  "PURCHASE PERIOD" means a period of six (6) months within
an Offering Period, except for the first Purchase Period as set forth in
Section 4(b).

             (r)  "PURCHASE PRICE" means with respect to a Purchase Period an
amount equal to 85% of the Fair Market Value (as defined in Section 7(b)
below) of a Share of Common Stock on the Offering Date or on the Purchase
Date, whichever is lower; provided, however, that in the event (i) of any
increase in the number of Shares available for issuance under the Plan as a
result of a stockholder-approved amendment to the Plan, and (ii) all or a
portion of such additional Shares are to be issued with respect to one or
more Offering Periods that are underway at the time of such increase
("ADDITIONAL SHARES"), and (iii) the Fair Market Value of a Share of Common
Stock on the date of such increase (the "APPROVAL DATE FAIR MARKET VALUE") is
higher than the Fair Market Value on the Offering Date for any such Offering
Period, then in such instance the Purchase Price with respect to Additional
Shares shall be 85% of the Approval Date Fair Market Value or the Fair Market
Value of a Share of Common Stock on the Purchase Date, whichever is lower.

             (s)  "SHARE" means a share of Common Stock, as adjusted in
accordance with Section 19 of the Plan.

             (t)  "SUBSIDIARY" means a corporation, domestic or foreign, of
which not less than 50% of the voting shares are held by the Company or a
Subsidiary, whether or not such corporation now exists or is hereafter
organized or acquired by the Company or a Subsidiary.

                                      -2-
<PAGE>

         3.  ELIGIBILITY.

             (a)  Any person who is an Employee as of the Offering Date of a
given Offering Period shall be eligible to participate in such Offering
Period under the Plan, subject to the requirements of Section 5(a) and the
limitations imposed by Section 423(b) of the Code.

             (b)  Any provisions of the Plan to the contrary notwithstanding,
no Employee shall be granted an option under the Plan (i) if, immediately
after the grant, such Employee (or any other person whose stock would be
attributed to such Employee pursuant to Section 424(d) of the Code) would own
capital stock of the Company and/or hold outstanding options to purchase
stock possessing five percent (5%) or more of the total combined voting power
or value of all classes of stock of the Company or of any subsidiary of the
Company, or (ii) if such option would permit his or her rights to purchase
stock under all employee stock purchase plans (described in Section 423 of
the Code) of the Company and its Subsidiaries to accrue at a rate which
exceeds Twenty-Five Thousand Dollars ($25,000) of the Fair Market Value (as
defined in Section 7(b) below) of such stock (determined at the time such
option is granted) for each calendar year in which such option is outstanding
at any time.

         4.  OFFERING PERIODS AND PURCHASE PERIODS.

             (a)  OFFERING PERIODS.  The Plan shall be implemented by a
series of Offering Periods of approximately twenty-four (24) months duration,
with new Offering Periods commencing on or about February 1 and August 1 of
each year (or at such other time or times as may be determined by the Board
of Directors). The first Offering Period shall commence on the beginning of
the effective date of the Registration Statement on Form S-1 for the initial
public offering of the Company's Common Stock (the "IPO DATE") and continue
until July 31, 2002. The Plan shall continue until terminated in accordance
with Section 20 hereof. The Board of Directors of the Company shall have the
power to change the duration and/or the frequency of Offering Periods with
respect to future offerings without stockholder approval if such change is
announced at least five (5) days prior to the scheduled beginning of the
first Offering Period to be affected.

             (b)  PURCHASE PERIODS.  Each Offering Period shall consist of
four (4) consecutive Purchase Periods of approximately six (6) months'
duration. The last day of each Purchase Period shall be the "PURCHASE DATE"
for such Purchase Period. A Purchase Period commencing on February 1 shall
end on the next July 31. A Purchase Period commencing on August 1 shall end
on the next January 31. The first Purchase Period shall commence on the IPO
Date and shall end on January 31, 2001. The Board of Directors of the Company
shall have the power to change the duration and/or frequency of Purchase
Periods with respect to future purchases without stockholder approval if such
change is announced at least five (5) days prior to the scheduled beginning
of the first Purchase Period to be affected.

         5.  PARTICIPATION.

             (a)  An eligible Employee may become a participant in the Plan
by completing a subscription agreement on the form provided by the Company
and filing it with the Company

                                      -3-
<PAGE>

prior to the applicable Offering Date. The subscription agreement shall set
forth the percentage of the participant's Compensation (subject to Section
6(a) below) to be paid as Contributions pursuant to the Plan.

             (b)  Payroll deductions shall commence on the first payroll paid
following the Offering Date and shall end on the last payroll paid on or
prior to the last Purchase Period of the Offering Period to which the
subscription agreement is applicable, unless sooner terminated by the
participant as provided in Section 10.

         6.  METHOD OF PAYMENT OF CONTRIBUTIONS.

             (a)  A participant shall elect to have payroll deductions made
on each payday during the Offering Period in an amount not less than one
percent (1%) and not more than twenty percent (20%) (or such greater
percentage as the Board may establish from time to time before an Offering
Date) of such participant's Compensation on each payday during the Offering
Period; provided that to the extent a participant is participating in more
than one Offering Period, the maximum aggregate percentage of Compensation
that he or she may contribute under the Plan shall be twenty percent (20%)
(or such greater percentage as the Board may establish from time to time
before an Offering Date). All payroll deductions made by a participant shall
be credited to his or her account under the Plan. A participant may not make
any additional payments into such account.

             (b)  A participant may discontinue his or her participation in
the Plan as provided in Section 10, or, on one occasion only during a
Purchase Period may increase and on one occasion only during a Purchase
Period may decrease the rate of his or her Contributions with respect to the
Offering Period by completing and filing with the Company a new subscription
agreement authorizing a change in the payroll deduction rate. The change in
rate shall be effective as of the beginning of the next calendar month
following the date of filing of the new subscription agreement, if the
agreement is filed at least ten (10) business days prior to such date and, if
not, as of the beginning of the next succeeding calendar month.

             (c)  Notwithstanding the foregoing, to the extent necessary to
comply with Section 423(b)(8) of the Code and Section 3(b), a participant's
payroll deductions may be decreased by the Company to 0% at any time during a
Purchase Period. Payroll deductions shall re-commence at the rate provided in
such participant's subscription agreement at the beginning of the first
Purchase Period which is scheduled to end in the following calendar year,
unless terminated by the participant as provided in Section 10. In addition,
a participant's payroll deductions may be decreased by the Company to 0% at
any time during a Purchase Period in order to avoid unnecessary payroll
contributions as a result of application of the maximum share limit set forth
in Section 7(a), or as a result of the limitations set forth in Section 3(b),
in which case payroll deductions shall re-commence at the rate provided in
such participant's subscription agreement at the beginning of the next
Purchase Period, unless terminated by the participant as provided in Section
10.

                                      -4-
<PAGE>

         7.  GRANT OF OPTION.

             (a)  On the Offering Date of each Offering Period, each eligible
Employee participating in such Offering Period shall be granted an option to
purchase on each Purchase Date a number of Shares of the Company's Common
Stock determined by dividing such Employee's Contributions accumulated prior
to such Purchase Date and retained in the participant's account as of the
Purchase Date by the applicable Purchase Price; provided however that the
maximum number of Shares an Employee may purchase during each Purchase Period
shall be 1,800 Shares (subject to any adjustment pursuant to Section 19
below), and provided further that such purchase shall be subject to the
limitations set forth in Sections 3(b) and 13.

             (b)  The fair market value of the Company's Common Stock on a
given date (the "FAIR MARKET VALUE") shall be determined by the Board in its
discretion; provided that to the extent the Common Stock is trading on the
Nasdaq National Market (i) the Fair Market Value as of an Offering Date shall
be the closing sales price of the Common Stock as reported by the Nasdaq
National Market for the last trading day immediately preceding the Offering
Date, and (ii) the Fair Market Value of the Common Stock as of a Purchase
Date shall be the closing sales price of the Common Stock as reported by the
Nasdaq National Market for the Purchase Date, in each case as reported in THE
WALL STREET JOURNAL.  For purposes of the Offering Date under the first
Offering Period under the Plan, the Fair Market Value of a share of the
Common Stock of the Company shall be the Price to Public as set forth in the
final prospectus filed with the Securities and Exchange Commission pursuant
to Rule 424 under the Securities Act of 1933, as amended.

         8.  EXERCISE OF OPTION.  Unless a participant withdraws from the
Plan as provided in Section 10, his or her option for the purchase of Shares
will be exercised automatically on each Purchase Date of an Offering Period,
and the maximum number of full Shares subject to the option will be purchased
at the applicable Purchase Price with the accumulated Contributions in his or
her account. No fractional Shares shall be issued. The Shares purchased upon
exercise of an option hereunder shall be deemed to be transferred to the
participant on the Purchase Date. During his or her lifetime, a participant's
option to purchase Shares hereunder is exercisable only by him or her.

         9.  DELIVERY.  As promptly as practicable after each Purchase Date
of each Offering Period, the Company shall arrange the delivery to each
participant, as appropriate, the Shares purchased upon exercise of his or her
option. No fractional Shares shall be purchased; any payroll deductions
accumulated in a participant's account which are not sufficient to purchase a
full Share shall be retained in the participant's account for the subsequent
Purchase Period or Offering Period, subject to earlier withdrawal by the
participant as provided in Section 10 below. Any other amounts left over in a
participant's account after a Purchase Date shall be returned to the
participant.

         10.  VOLUNTARY WITHDRAWAL; TERMINATION OF EMPLOYMENT.

             (a)  A participant may withdraw all but not less than all the
Contributions credited to his or her account under the Plan at any time prior
to each Purchase Date by giving

                                      -5-
<PAGE>

written notice to the Company. All of the participant's Contributions
credited to his or her account will be paid to him or her promptly after
receipt of his or her notice of withdrawal and his or her option for the
current period will be automatically terminated, and no further Contributions
for the purchase of Shares will be made during the Offering Period.

             (b)  Upon termination of the participant's Continuous Status as
an Employee prior to the Purchase Date of an Offering Period for any reason,
including retirement or death, the Contributions credited to his or her
account will be returned to him or her or, in the case of his or her death,
to the person or persons entitled thereto under Section 15, and his or her
option will be automatically terminated.

             (c)  In the event an Employee fails to remain in Continuous
Status as an Employee of the Company for at least twenty (20) hours per week
during the Offering Period in which the employee is a participant, he or she
will be deemed to have elected to withdraw from the Plan and the
Contributions credited to his or her account will be returned to him or her
and his or her option terminated.

             (d)  A participant's withdrawal from an offering will not have
any effect upon his or her eligibility to participate in a succeeding
offering or in any similar plan which may hereafter be adopted by the Company.

         11.  AUTOMATIC WITHDRAWAL.  To the extent permitted by any
applicable laws, regulations or stock exchange rules, if the Fair Market
Value of the Shares on an Offering Date for an Offering Period (the "NEW
OFFERING PERIOD") commencing within an Offering Period (the "ONGOING OFFERING
PERIOD") then in progress is lower than was the Fair Market Value of the
Shares on the Offering Date for the Ongoing Offering Period, then every
participant in the Ongoing Offering Period shall automatically be deemed to
have (i) withdrawn from the Ongoing Offering Period at the close of the
Purchase Period immediately preceding the New Offering Period, and (ii)
enrolled in such New Offering Period. In addition, participants shall
automatically be withdrawn as of July 31, 2000 from the Offering Period
beginning on the IPO Date and re-enrolled in the Offering Period beginning on
August 1, 2000 if the Fair Market Value of the Shares on the IPO Date is
greater than the Fair Market Value of the Shares for the August 1, 2000
Offering Date, unless a participant notifies the Administrator prior to July
31, 2000 that he or she does not wish to be withdrawn and re-enrolled under
these circumstances.

         12.  INTEREST.  No interest shall accrue on the Contributions of a
participant in the Plan.

         13.  STOCK.

             (a)  Subject to adjustment as provided in Section 19, the
maximum number of Shares which shall be made available for sale under the
Plan shall be 350,000 Shares, plus an annual increase on the first day of
each of the Company's fiscal years beginning in 2001 and ending in 2010 equal
to the lesser of (i) 350,000 Shares, (ii) one and four-tenths percent (1.4%)
of the Shares outstanding on the last day of the immediately preceding fiscal
year, or (iii) such lesser number of Shares as is determined by the Board. If
the Board determines that, on a given

                                      -6-
<PAGE>

Purchase Date, the number of shares with respect to which options are to be
exercised may exceed (i) the number of shares of Common Stock that were
available for sale under the Plan on the Offering Date of the applicable
Offering Period, or (ii) the number of shares available for sale under the
Plan on such Purchase Date, the Board may in its sole discretion provide (x)
that the Company shall make a pro rata allocation of the Shares of Common
Stock available for purchase on such Offering Date or Purchase Date, as
applicable, in as uniform a manner as shall be practicable and as it shall
determine in its sole discretion to be equitable among all participants
exercising options to purchase Common Stock on such Purchase Date, and
continue all Offering Periods then in effect, or (y) that the Company shall
make a pro rata allocation of the shares available for purchase on such
Offering Date or Purchase Date, as applicable, in as uniform a manner as
shall be practicable and as it shall determine in its sole discretion to be
equitable among all participants exercising options to purchase Common Stock
on such Purchase Date, and terminate any or all Offering Periods then in
effect pursuant to Section 20 below. The Company may make pro rata allocation
of the Shares available on the Offering Date of any applicable Offering
Period pursuant to the preceding sentence, notwithstanding any authorization
of additional Shares for issuance under the Plan by the Company's
stockholders subsequent to such Offering Date.

             (b)  The participant shall have no interest or voting right in
Shares covered by his or her option until such option has been exercised.

             (c)  Shares to be delivered to a participant under the Plan will
be registered in the name of the participant or in the name of the
participant and his or her spouse.

         14.  ADMINISTRATION.  The Board, or a committee named by the Board,
shall supervise and administer the Plan and shall have full power to adopt,
amend and rescind any rules deemed desirable and appropriate for the
administration of the Plan and not inconsistent with the Plan, to construe
and interpret the Plan, and to make all other determinations necessary or
advisable for the administration of the Plan.

         15.  DESIGNATION OF BENEFICIARY.

             (a)  A participant may file a written designation of a
beneficiary who is to receive any Shares and cash, if any, from the
participant's account under the Plan in the event of such participant's death
subsequent to the end of a Purchase Period but prior to delivery to him or
her of such Shares and cash. In addition, a participant may file a written
designation of a beneficiary who is to receive any cash from the
participant's account under the Plan in the event of such participant's death
prior to the Purchase Date of an Offering Period. If a participant is married
and the designated beneficiary is not the spouse, spousal consent shall be
required for such designation to be effective.

             (b)  Such designation of beneficiary may be changed by the
participant (and his or her spouse, if any) at any time by written notice. In
the event of the death of a participant and in the absence of a beneficiary
validly designated under the Plan who is living at the time of such
participant's death, the Company shall deliver such Shares and/or cash to the
executor or administrator of the estate of the participant, or if no such
executor or administrator has been

                                      -7-
<PAGE>

appointed (to the knowledge of the Company), the Company, in its discretion,
may deliver such Shares and/or cash to the spouse or to any one or more
dependents or relatives of the participant, or if no spouse, dependent or
relative is known to the Company, then to such other person as the Company
may designate.

         16.  TRANSFERABILITY.  Neither Contributions credited to a
participant's account nor any rights with regard to the exercise of an option
or to receive Shares under the Plan may be assigned, transferred, pledged or
otherwise disposed of in any way (other than by will, the laws of descent and
distribution, or as provided in Section 15) by the participant. Any such
attempt at assignment, transfer, pledge or other disposition shall be without
effect, except that the Company may treat such act as an election to withdraw
funds in accordance with Section 10.

         17.  USE OF FUNDS.  All Contributions received or held by the
Company under the Plan may be used by the Company for any corporate purpose,
and the Company shall not be obligated to segregate such Contributions.

         18.  REPORTS.  Individual accounts will be maintained for each
participant in the Plan. Statements of account will be given to participating
Employees at least annually, which statements will set forth the amounts of
Contributions, the per Share Purchase Price, the number of Shares purchased
and the remaining cash balance, if any.

         19.  ADJUSTMENTS UPON CHANGES IN CAPITALIZATION; CORPORATE
TRANSACTIONS.

             (a)  ADJUSTMENT.  Subject to any required action by the
stockholders of the Company, the number of Shares covered by each option
under the Plan which has not yet been exercised and the number of Shares
which have been authorized for issuance under the Plan but have not yet been
placed under option (collectively, the "RESERVES"), as well as the maximum
number of shares of Common Stock which may be purchased by a participant in a
Purchase Period, the number of shares of Common Stock set forth in Section
13(a) above, and the price per Share of Common Stock covered by each option
under the Plan which has not yet been exercised, shall be proportionately
adjusted for any increase or decrease in the number of issued Shares
resulting from a stock split, reverse stock split, stock dividend,
combination or reclassification of the Common Stock (including any such
change in the number of Shares of Common Stock effected in connection with a
change in domicile of the Company), or any other increase or decrease in the
number of Shares effected without receipt of consideration by the Company;
provided however that conversion of any convertible securities of the Company
shall not be deemed to have been "effected without receipt of consideration."
Such adjustment shall be made by the Board, whose determination in that
respect shall be final, binding and conclusive. Except as expressly provided
herein, no issue 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 an option.

             (b)  CORPORATE TRANSACTIONS.  In the event of a dissolution or
liquidation of the Company, any Purchase Period and Offering Period then in
progress will terminate immediately prior to the consummation of such action,
unless otherwise provided by the Board. In the event of a Corporate
Transaction, each option outstanding under the Plan shall be assumed

                                      -8-
<PAGE>

or an equivalent option shall be substituted by the successor corporation or
a parent or Subsidiary of such successor corporation. In the event that the
successor corporation refuses to assume or substitute for outstanding
options, each Purchase Period and Offering Period then in progress shall be
shortened and a new Purchase Date shall be set (the "NEW PURCHASE DATE"), as
of which date any Purchase Period and Offering Period then in progress will
terminate. The New Purchase Date shall be on or before the date of
consummation of the transaction and the Board shall notify each participant
in writing, at least ten (10) days prior to the New Purchase Date, that the
Purchase Date for his or her option has been changed to the New Purchase Date
and that his or her option will be exercised automatically on the New
Purchase Date, unless prior to such date he or she has withdrawn from the
Offering Period as provided in Section 10. For purposes of this Section 19,
an option granted under the Plan shall be deemed to be assumed, without
limitation, if, at the time of issuance of the stock or other consideration
upon a Corporate Transaction, each holder of an option under the Plan would
be entitled to receive upon exercise of the option the same number and kind
of shares of stock or the same amount of property, cash or securities as such
holder would have been entitled to receive upon the occurrence of the
transaction if the holder had been, immediately prior to the transaction, the
holder of the number of Shares of Common Stock covered by the option at such
time (after giving effect to any adjustments in the number of Shares covered
by the option as provided for in this Section 19); provided however that if
the consideration received in the transaction is not solely common stock of
the successor corporation or its parent (as defined in Section 424(e) of the
Code), the Board may, with the consent of the successor corporation, provide
for the consideration to be received upon exercise of the option to be solely
common stock of the successor corporation or its parent equal in Fair Market
Value to the per Share consideration received by holders of Common Stock in
the transaction.

         The Board may, if it so determines in the exercise of its sole
discretion, also make provision for adjusting the Reserves, as well as the
price per Share of Common Stock covered by each outstanding option, in the
event that the Company effects one or more reorganizations,
recapitalizations, rights offerings or other increases or reductions of
Shares of its outstanding Common Stock, and in the event of the Company's
being consolidated with or merged into any other corporation.

         20.  AMENDMENT OR TERMINATION.

             (a)  The Board may at any time and for any reason terminate or
amend the Plan. Except as provided in Section 19, no such termination of the
Plan may affect options previously granted, provided that the Plan or an
Offering Period may be terminated by the Board on a Purchase Date or by the
Board's setting a new Purchase Date with respect to an Offering Period and
Purchase Period then in progress if the Board determines that termination of
the Plan and/or the Offering Period is in the best interests of the Company
and the stockholders or if continuation of the Plan and/or the Offering
Period would cause the Company to incur adverse accounting charges as a
result of a change after the effective date of the Plan in the generally
accepted accounting rules applicable to the Plan. Except as provided in
Section 19 and in this Section 20, no amendment to the Plan shall make any
change in any option previously granted which adversely affects the rights of
any participant. In addition, to the extent necessary to

                                      -9-
<PAGE>

comply with Rule 16b-3 under the Exchange Act, or under Section 423 of the
Code (or any successor rule or provision or any applicable law or
regulation), the Company shall obtain stockholder approval in such a manner
and to such a degree as so required.

             (b)  Without stockholder consent and without regard to whether
any participant rights may be considered to have been adversely affected, the
Board (or its committee) shall be entitled to change the Offering Periods and
Purchase Periods, limit the frequency and/or number of changes in the amount
withheld during an Offering Period, establish the exchange ratio applicable
to amounts withheld in a currency other than U.S. dollars, permit payroll
withholding in excess of the amount designated by a participant in order to
adjust for delays or mistakes in the Company's processing of properly
completed withholding elections, establish reasonable waiting and adjustment
periods and/or accounting and crediting procedures to ensure that amounts
applied toward the purchase of Common Stock for each participant properly
correspond with amounts withheld from the participant's Compensation, and
establish such other limitations or procedures as the Board (or its
committee) determines in its sole discretion advisable which are consistent
with the Plan.

         21.  NOTICES.  All notices or other communications by a participant
to the Company under or in connection with the Plan shall be deemed to have
been duly given when received in the form specified by the Company at the
location, or by the person, designated by the Company for the receipt thereof.

         22.  CONDITIONS UPON ISSUANCE OF SHARES.  Shares shall not be issued
with respect to an option unless the exercise of such option and the issuance
and delivery of such Shares pursuant thereto shall comply with all applicable
provisions of law, domestic or foreign, including, without limitation, the
Securities Act of 1933, as amended, the Exchange Act, the rules and
regulations promulgated thereunder, applicable state securities laws and the
requirements of any stock exchange upon which the Shares may then be listed,
and shall be further subject to the approval of counsel for the Company with
respect to such compliance.

         As a condition to the exercise of an option, the Company may require
the person exercising such option to represent and warrant at the time of any
such exercise that the Shares are being purchased only for investment and
without any present intention to sell or distribute such Shares if, in the
opinion of counsel for the Company, such a representation is required by any
of the aforementioned applicable provisions of law.

         23.  TERM OF PLAN; EFFECTIVE DATE.  The Plan shall become effective
upon the IPO Date. It shall continue in effect for a term of twenty (20)
years unless sooner terminated under Section 20.

                                      -10-
<PAGE>

                           ROSETTA INPHARMATICS, INC.

                        2000 EMPLOYEE STOCK PURCHASE PLAN
                             SUBSCRIPTION AGREEMENT


                                                          New Election
                                                                       ---------
                                                    Change of Election
                                                                       ---------


         1.  I, ________________________, hereby elect to participate in the
Rosetta Inpharmatics, Inc. 2000 Employee Stock Purchase Plan (the "PLAN") for
the Offering Period ______________, ____ to _______________, ____, and
subscribe to purchase shares of the Company's Common Stock in accordance with
this Subscription Agreement and the Plan.

         2.  I elect to have Contributions in the amount of ____% of my
Compensation, as those terms are defined in the Plan, applied to this
purchase. I understand that this amount (together with any other amounts I am
contributing under the Plan) must not be less than 1% and not more than 20%
of my Compensation during the Offering Period. (Please note that no
fractional percentages are permitted).

         3.  I hereby authorize payroll deductions from each paycheck during
the Offering Period at the rate stated in Item 2 of this Subscription
Agreement. I understand that all payroll deductions made by me shall be
credited to my account under the Plan and that I may not make any additional
payments into such account. I understand that all payments made by me shall
be accumulated for the purchase of shares of Common Stock at the applicable
purchase price determined in accordance with the Plan. I further understand
that, except as otherwise set forth in the Plan, shares will be purchased for
me automatically on the Purchase Date of each Offering Period unless I
otherwise withdraw from the Plan by giving written notice to the Company for
such purpose.

         4.  I understand that I may discontinue at any time prior to the
Purchase Date my participation in the Plan as provided in Section 10 of the
Plan. I also understand that I can increase or decrease the rate of my
Contributions on one occasion only with respect to any increase and one
occasion only with respect to any decrease during any Purchase Period by
completing and filing a new Subscription Agreement with such increase or
decrease taking effect as of the beginning of the calendar month following
the date of filing of the new Subscription Agreement, if filed at least ten
(10) business days prior to the beginning of such month. Further, I may
change the rate of deductions for future Offering Periods by filing a new
Subscription Agreement, and any such change will be effective as of the
beginning of the next Offering Period. In addition, I acknowledge that,
unless I discontinue my participation in the Plan as provided in Section 10
of the Plan, my election will continue to be effective for each successive
Offering Period.

<PAGE>

         5.  I have received a copy of the Company's most recent description
of the Plan and a copy of the complete "Rosetta Inpharmatics, Inc. 2000
Employee Stock Purchase Plan." I understand that my participation in the Plan
is in all respects subject to the terms of the Plan.

         6.  Shares purchased for me under the Plan should be issued in the
name(s) of (name of employee or employee and spouse only):



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


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

         7.  In the event of my death, I hereby designate the following as my
beneficiary(ies) to receive all payments and shares due to me under the Plan:


NAME:  (Please print)
                                           ------------------------------------
                                           (First)       (Middle)        (Last)


--------------------                       -------------------------------------
(Relationship)                             (Address)


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

         8.  I understand that if I dispose of any shares received by me
pursuant to the Plan within 2 years after the Offering Date (the first day of
the Offering Period during which I purchased such shares) or within 1 year
after the Purchase Date, I will be treated for federal income tax purposes as
having received ordinary compensation income at the time of such disposition
in an amount equal to the excess of the fair market value of the shares on
the Purchase Date over the price which I paid for the shares, regardless of
whether I disposed of the shares at a price less than their fair market value
at the Purchase Date. The remainder of the gain or loss, if any, recognized
on such disposition will be treated as capital gain or loss.

         I HEREBY AGREE TO NOTIFY THE COMPANY IN WRITING WITHIN 30 DAYS AFTER
THE DATE OF ANY SUCH DISPOSITION, AND I WILL MAKE ADEQUATE PROVISION FOR
FEDERAL, STATE OR OTHER TAX WITHHOLDING OBLIGATIONS, IF ANY, WHICH ARISE UPON
THE DISPOSITION OF THE COMMON STOCK.  The Company may, but will not be
obligated to, withhold from my compensation the amount necessary to meet any
applicable withholding obligation including any withholding necessary to make
available to the Company any tax deductions or benefits attributable to the
sale or early disposition of Common Stock by me.

         9.  If I dispose of such shares at any time after expiration of the
2-year and 1-year holding periods, I understand that I will be treated for
federal income tax purposes as having received compensation income only to
the extent of an amount equal to the lesser of (1) the excess of the fair
market value of the shares at the time of such disposition over the purchase
price which I paid for the shares under the option, or (2) 15% of the fair
market value of the

                                      -2-
<PAGE>

shares on the Offering Date. The remainder of the gain or loss, if any,
recognized on such disposition will be treated as capital gain or loss.

         I UNDERSTAND THAT THIS TAX SUMMARY IS ONLY A SUMMARY AND IS SUBJECT
TO CHANGE.  I further understand that I should consult a tax advisor
concerning the tax implications of the purchase and sale of stock under the
Plan.

         10.  In connection with the initial public offering of the Company's
securities and upon request of the Company or the underwriters managing any
underwritten offering of the Company's securities, I agree not to sell, make
any short sale of, loan, grant any option for the purchase of, or otherwise
dispose of any securities of the Company, however or whenever I acquired
them, without the prior written consent of the Company or such underwriters,
as the case may be, for such period of time (not to exceed 180 days) from the
effective date of such registration as may be requested by the Company or
such managing underwriters and to execute an agreement reflecting the
foregoing as may be requested by the underwriters at the time of the public
offering.

         11.  I hereby agree to be bound by the terms of the Plan. The
effectiveness of this Subscription Agreement is dependent upon my eligibility
to participate in the Plan.

SIGNATURE:
           -----------------------------------------

SOCIAL SECURITY #:
                   ---------------------------------

DATE:
      ----------------------------------------------



SPOUSE'S SIGNATURE (necessary if beneficiary is
not spouse):



-----------------------------------------------------
(Signature)


-----------------------------------------------------
(Print name)





                                      -3-
<PAGE>

                           ROSETTA INPHARMATICS, INC.

                        2000 EMPLOYEE STOCK PURCHASE PLAN

                              NOTICE OF WITHDRAWAL

         I, __________________________, hereby elect to withdraw my
participation in the Rosetta Inpharmatics, Inc. 2000 Employee Stock Purchase
Plan (the "PLAN") for the Offering Period that began on _________ ___, _____.
This withdrawal covers all Contributions credited to my account and is
effective on the date designated below.

         I understand that all Contributions credited to my account will be
paid to me within ten (10) business days of receipt by the Company of this
Notice of Withdrawal and that my option for the current period will
automatically terminate, and that no further Contributions for the purchase
of shares can be made by me during the Offering Period.

         The undersigned further understands and agrees that he or she shall
be eligible to participate in succeeding offering periods only by delivering
to the Company a new Subscription Agreement.



Dated:
       ---------------------           ----------------------------------------
                                       Signature of Employee


                                       ----------------------------------------
                                       Social Security Number