<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


<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). If
and to the extent the Board takes action prior to the effective date of the
Company's Registration Statement on Form S-1 for the initial public offering of
the Company's Common Stock (the "IPO DATE") to grant eligible Employees options
to participate in an Offering Period beginning on the IPO Date (such period, the
"IPO Offering Period"), then such period shall begin on 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.
If the Board takes action to cause there to be an IPO Offering Period, then the
first Purchase Period shall begin on the IPO Date and 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.


                                      -3-
<PAGE>

     5.   PARTICIPATION.

          (a)  Except with respect to the IPO Offering Period, if any, 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 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. With
respect to the IPO Offering Period, if any, an eligible Employee will become a
participant in the Plan by the Board's taking action prior to the IPO Date to
grant such persons options to purchase Shares pursuant to the Plan. Such options
shall allow eligible Employees to participate in the Plan and purchase stock on
applicable Purchase Dates by (a) making a lump sum cash payment to the Company
prior to the time of purchase for each applicable Purchase Date for the amount
of the purchase price for the Shares being purchased or (b) electing, following
the IPO Date, to have amounts directly withheld from the Employee's Compensation
pursuant to Section 6 below.

          (b)  Except with respect to the IPO Offering Period, if any, 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. With respect to
the IPO Offering Period, payroll deductions shall commence on the first payroll
date following the date, if any, on which the participant elects to have amounts
withheld from his or her Compensation. To the extent a participant in the IPO
Offering Period does not elect to have amounts withheld from Compensation, the
participant shall continue (unless he or she withdraws from the Plan pursuant to
Section 10 below) to have an option to purchase Shares under the Plan on
applicable Purchase Dates, which options shall be exercised, if at all, through
lump sum payments in cash to the Company prior to the time of purchase for each
applicable Purchase Date.

     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, except with respect to the IPO Offering
Period, if any, on one occasion only during a



                                      -4-
<PAGE>

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. With respect to the IPO Offering Period, an
election by a participant to commence payroll deductions under the Plan
following the IPO Date at a rate of Compensation that would result in his or her
purchasing less than the full amount of Shares that he or she could purchase
under the option granted to him or her by the Board shall not count as a
decrease in participation for purposes of the first sentence of this subsection.

          (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.

     7.   GRANT OF OPTION.

          (a)  Except with respect to the IPO Offering Period, if any, and
subject to the final sentence of this Section 7(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.
With respect to the IPO Offering Period, if any, each eligible Employee shall be
granted an option to purchase on each Purchase Date a number of Shares of the
Company's Common Stock determined by dividing the maximum amount specified by
the Board in granting the option (which amount shall be a percentage of such
Employee's Compensation) by the applicable Purchase Price. Notwithstanding the
above, the maximum number of Shares an Employee may purchase during each
Purchase Period of any Offering Period (including the IPO Offering 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


                                      -5-
<PAGE>

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 IPO
Offering Period, if any, 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. Except with respect to the IPO Offering Period, if
any, 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. With respect to the IPO
Offering Period, a participant's option thereunder shall either be exercised as
provided in the preceding sentence or by the participant's delivering to the
Company a check for the full amount of the purchase price of the Shares being
purchased (which number of Shares may be less than the entire number of Shares
subject to the option granted by the Board) prior to the time of purchase for
the applicable Purchase Date. 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 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. With respect to the IPO Offering Period, if any, a participant who has
not chosen to have amounts withheld from his or her Compensation shall be
considered to have withdrawn from such


                                      -6-
<PAGE>

period if he or she fails to exercise the options granted hereunder by
delivering to the Company the full amount of the purchase price for the Shares
being purchased (which number of Shares may be less than the entire number of
Shares subject to the option granted by the Board) for the first applicable
Purchase Period within the IPO 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.

     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


                                      -7-
<PAGE>

lesser number of Shares as is determined by the Board. If the Board determines
that, on a given 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


                                      -8-
<PAGE>

administrator of the estate of the participant, or if no such executor or
administrator has been 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.


                                      -9-
<PAGE>

In the event of a Corporate Transaction, each option outstanding under the Plan
shall be assumed 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


                                      -10-
<PAGE>

which adversely affects the rights of any participant. In addition, to the
extent necessary to 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.


                                      -11-
<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