<PAGE>   1
                                                                    EXHIBIT 4.13


                                VIROLOGIC, INC.

                                 1996 STOCK PLAN

                             STOCK OPTION AGREEMENT
--------------------------------------------------------------------------------

        Unless otherwise defined herein, the terms defined in the Plan shall
have the same defined meanings in this Option Agreement.

I.      NOTICE OF STOCK OPTION GRANT

[Name]
[Address]

        You have been granted an option to purchase Common Stock of the Company,
subject to the terms and conditions of the Plan and this Option Agreement, as
follows:

        Date of Grant

        Vesting Commencement Date

        Exercise Price per Share

        Total Number of Shares Granted

        Total Exercise Price

        Type of Option:                          ___Incentive Stock Option

                                                 ___Nonstatutory Stock Option

        Term/Expiration Date:



                                       1.
<PAGE>   2
        VESTING SCHEDULE:

        This Option may be exercised, in whole or in part, in accordance with
the following schedule:

         [Vesting Schdule]

        TERMINATION PERIOD:

         This Option may be exercised for 30 days after termination of
employment or consulting relationship, or such longer period as may be
applicable upon death or disability of Optionee as provided in the Plan, but in
no event later than the Term/Expiration Date as provided above.

II.     AGREEMENT

               1. GRANT OF OPTION. ViroLogic, Inc., a Delaware corporation (the
"Company"), hereby grants to the Optionee named in the Notice of Grant (the
"Optionee"), an option (the "Option") to purchase the total number of shares of
Common Stock (the "Shares") set forth in the Notice of Grant, at the exercise
price per share set forth in the Notice of Grant (the "Exercise Price") subject
to the terms, definitions and provisions of the 1996 Stock Plan (the "Plan")
adopted by the Company, which is incorporated herein by reference. Unless
otherwise defined herein, the terms defined in the Plan shall have the same
defined meanings in this Option.

              If designated in the Notice of Grant as an Incentive Stock Option
("ISO"), this Option is intended to qualify as an Incentive Stock Option as
defined in Section 422 of the Code. However, if this Option is intended to be an
Incentive Stock Option, to the extent that it exceeds the $100,000 rule of Code
Section 422(d) it shall be treated as a Nonstatutory Stock Option ("NSO").

               2. EXERCISE OF OPTION. This Option shall be exercisable during
its term in accordance with the Vesting Schedule set out in the Notice of Grant
and with the provisions of Section 9 of the Plan as follows:

                      a.     RIGHT TO EXERCISE.

                             (i) This Option may not be exercised for a fraction
of a Share.

                             (ii) In the event of Optionee's death, disability
or other termination of the employment or consulting relationship, the
exercisability of the Option is governed by Sections 5, 6 and 7 below, subject
to the limitation contained in subsection 2(a)(iii).

                             (iii) In no event may this Option be exercised
after the date of expiration of the term of this Option as set forth in the
Notice of Grant.

                      b. METHOD OF EXERCISE. This Option shall be exercisable by
written notice (in the form attached as Exhibit A) which shall state the
election to exercise the Option, the number of Shares in respect of which option
is being exercised, and such other



                                       2.
<PAGE>   3
representations and agreements as to the holder's investment intent with respect
to such shares of Common Stock as may be required by the Company pursuant to the
provisions of the Plan. Such written notice shall be signed by the Optionee and
shall be delivered in person or by certified mail to the Secretary of the
Company. The written notice shall be accompanied by payment of the Exercise
Price. This Option shall be deemed to be exercised upon receipt by the Company
of such written notice accompanied by the Exercise Price.

              No Shares will be issued pursuant to the exercise of an Option
unless such issuance and such exercise shall comply with all relevant provisions
of law and the requirements of any stock exchange upon which the Shares may then
be listed. Assuming such compliance, for income tax purposes the Shares shall be
considered transferred to the Optionee on the date on which the Option is
exercised with respect to such Shares.

               3. OPTIONEE'S REPRESENTATIONS. In the event the Shares
purchasable pursuant to the exercise of this Option have not been registered
under the Securities Act of 1933, as amended, at the time this Option is
exercised, Optionee shall, if required by the Company, concurrently with the
exercise of all or any portion of this Option, deliver to the Company his or her
Investment Representation Statement in the form attached hereto as Exhibit B,
and shall read the applicable rules of the Commissioner of Corporations attached
to such Investment Representation Statement.

               4. METHOD OF PAYMENT. Payment of the Exercise Price shall be by
any of the following, or a combination thereof, at the election of the Optionee:

                      a. cash; or

                      b. check; or

                      c. surrender of other shares of Common Stock of the
Company which (A) in the case of Shares acquired pursuant to the exercise of a
Company option, have been owned by the Optionee for more than six (6) months on
the date of surrender, and (B) have a Fair Market Value on the date of surrender
equal to the Exercise Price of the Shares as to which the Option is being
exercised; or

                      d. delivery of a properly executed exercise notice
together with such other documentation as the Administrator and the broker, if
applicable, shall require to effect an exercise of the Option and delivery to
the Company of the sale or loan proceeds required to pay the Exercise Price.

               5. TERMINATION OF RELATIONSHIP. In the event an Optionee's
Continuous Status as an Employee or Consultant terminates, Optionee may, to the
extent otherwise so entitled at the date of such termination (the "Termination
Date"), exercise this Option during the Termination Period set out in the Notice
of Grant. To the extent that Optionee was not entitled to exercise this Option
at the date of such termination, or if Optionee does not exercise this Option
within the time specified herein, the Option shall terminate.

               6. DISABILITY OF OPTIONEE. Notwithstanding the provisions of
Section 5 above, in the event of termination of an Optionee's consulting
relationship or Continuous Status



                                       3.
<PAGE>   4
as an Employee as a result of his or her disability, Optionee may, but only
within six (6) months from the date of such termination (and in no event later
than the expiration date of the term of such Option as set forth in the Option
Agreement), exercise the Option to the extent otherwise entitled to exercise it
at the date of such termination; provided, however, that if such disability is
not a "disability" as such term is defined in Section 22(e)(3) of the Code, in
the case of an Incentive Stock Option such Incentive Stock Option shall
automatically convert to a Nonstatutory Stock Option on the day three months and
one day following such termination. To the extent that Optionee was not entitled
to exercise the Option at the date of termination, or if Optionee does not
exercise such Option to the extent so entitled within the time specified herein,
the Option shall terminate, and the Shares covered by such Option shall revert
to the Plan.

               7. DEATH OF OPTIONEE. In the event of termination of Optionee's
Continuous Status as an Employee or Consultant as a result of the death of
Optionee, the Option may be exercised at any time within twelve (12) months
following the date of death (but in no event later than the date of expiration
of the term of this Option as set forth in Section 9 below), by Optionee's
estate or by a person who acquired the right to exercise the Option by bequest
or inheritance, but only to the extent the Optionee could exercise the Option at
the date of death.

               8. NON-TRANSFERABILITY OF OPTION. This Option may not be
transferred in any manner otherwise than by will or by the laws of descent or
distribution and may be exercised during the lifetime of Optionee only by
Optionee. The terms of this Option shall be binding upon the executors,
administrators, heirs, successors and assigns of the Optionee.

               9. TERM OF OPTION. This Option may be exercised only within the
term set out in the Notice of Grant, and may be exercised during such term only
in accordance with the Plan and the terms of this Option. The limitations set
out in Section 7 of the Plan regarding Options designated as Incentive Stock
Options and Options granted to more than ten percent (10%) shareholders shall
apply to this Option.

               10. TAXATION UPON EXERCISE OF OPTION. Optionee understands that,
upon exercising a Nonstatutory Option, he or she will recognize income for tax
purposes in an amount equal to the excess of the then Fair Market Value of the
Shares over the exercise price. However, the timing of this income recognition
may be deferred for up to six months if Optionee is subject to Section 16 of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"). If the
Optionee is an Employee, the Company will be required to withhold from
Optionee's compensation, or collect from Optionee and pay to the applicable
taxing authorities an amount equal to a percentage of this compensation income.
Additionally, the Optionee may at some point be required to satisfy tax
withholding obligations with respect to the disqualifying disposition of an
Incentive Stock Option. The Optionee shall satisfy his or her tax withholding
obligation arising upon the exercise of this Option out of Optionee's
compensation or by payment to the Company.

               11. TAX CONSEQUENCES. Set forth below is a brief summary as of
the date of this Option of some of the federal and California tax consequences
of exercise of this Option and disposition of the Shares. THIS SUMMARY IS
NECESSARILY INCOMPLETE, AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE.
OPTIONEE SHOULD



                                       4.
<PAGE>   5
CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE SHARES.

                      a. EXERCISE OF ISO. If this Option qualifies as an ISO,
there will be no regular federal income tax liability or California income tax
liability upon the exercise of the Option, although the excess, if any, of the
Fair Market Value of the Shares on the date of exercise over the Exercise Price
will be treated as an adjustment to the alternative minimum tax for federal tax
purposes and may subject the Optionee to the alternative minimum tax in the year
of exercise.

                      b. EXERCISE OF ISO FOLLOWING DISABILITY. If the Optionee's
Continuous Status as an Employee or Consultant terminates as a result of
disability that is not total and permanent disability as defined in Section
22(e)(3) of the Code, to the extent permitted on the date of termination, the
Optionee must exercise an ISO within 90 days of such termination for the ISO to
be qualified as an ISO.

                      c. EXERCISE OF NONSTATUTORY STOCK OPTION. There may be a
regular federal income tax liability and California income tax liability upon
the exercise of a Nonstatutory Stock Option. The Optionee will be treated as
having received compensation income (taxable at ordinary income tax rates) equal
to the excess, if any, of the Fair Market Value of the Shares on the date of
exercise over the Exercise Price. If Optionee is an Employee or a former
Employee, the Company will be required to withhold from Optionee's compensation
or collect from Optionee and pay to the applicable taxing authorities an amount
in cash equal to a percentage of this compensation income at the time of
exercise, and may refuse to honor the exercise and refuse to deliver Shares if
such withholding amounts are not delivered at the time of exercise.

                      d. DISPOSITION OF SHARES. In the case of an NSO, if Shares
are held for at least one year, any gain realized on disposition of the Shares
will be treated as long-term capital gain for federal and California income tax
purposes. In the case of an ISO, if Shares transferred pursuant to the Option
are held for at least one year after exercise and are disposed of at least two
years after the Date of Grant, any gain realized on disposition of the Shares
will also be treated as long-term capital gain for federal and California income
tax purposes. If Shares purchased under an ISO are disposed of within such
one-year period or within two years after the Date of Grant, any gain realized
on such disposition will be treated as compensation income (taxable at ordinary
income rates) to the extent of the difference between the Exercise Price and the
lesser of (1) the Fair Market Value of the Shares on the date of exercise, or
(2) the sale price of the Shares.

                      e. NOTICE OF DISQUALIFYING DISPOSITION OF ISO SHARES. If
the Option granted to Optionee herein is an ISO, and if Optionee sells or
otherwise disposes of any of the Shares acquired pursuant to the ISO on or
before the later of (1) the date two years after the Date of Grant, or (2) the
date one year after the date of exercise, the Optionee shall immediately notify
the Company in writing of such disposition. Optionee agrees that Optionee may be
subject to income tax withholding by the Company on the compensation income
recognized by the Optionee.



                                       5.
<PAGE>   6
               12. ENTIRE AGREEMENTS GOVERNING LAW. The Plan is incorporated
herein by reference. The Plan and this Option Agreement constitute the entire
agreement of the parties with respect to the subject matter hereof and supersede
in their entirety all prior undertakings and agreements of the Company and
Optionee with respect to the subject matter hereof, and may not be modified
adversely to the Optionee's interest except by means of a writing signed by the
Company and Optionee. This agreement is governed by California law except for
that body of law pertaining to conflict of laws.




                                       VIROLOGIC, INC.
                                       a Delaware corporation

                                       By:
                                          --------------------------------------

                                       Its:
                                           -------------------------------------



                                       6.
<PAGE>   7
        OPTIONEE ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES PURSUANT TO
THE OPTION HEREOF IS EARNED ONLY BY CONTINUING CONSULTANCY OR EMPLOYMENT AT THE
WILL OF THE COMPANY (NOT THROUGH THE ACT OF BEING HIRED, BEING GRANTED THIS
OPTION OR ACQUIRING SHARES HEREUNDER). OPTIONEE FURTHER ACKNOWLEDGES AND AGREES
THAT NOTHING IN THIS AGREEMENT, NOR IN THE COMPANY'S STOCK OPTION PLAN WHICH IS
INCORPORATED HEREIN BY REFERENCE, SHALL CONFER UPON OPTIONEE ANY RIGHT WITH
RESPECT TO CONTINUATION OF EMPLOYMENT OR CONSULTANCY BY THE COMPANY, NOR SHALL
IT INTERFERE IN ANY WAY WITH OPTIONEE'S RIGHT OR THE COMPANY'S RIGHT TO
TERMINATE OPTIONEE'S EMPLOYMENT OR CONSULTANCY AT ANY TIME, WITH OR WITHOUT
CAUSE.

          Optionee acknowledges receipt of a copy of the Plan and represents
   that he is familiar with the terms and provisions thereof, and hereby accepts
   this Option subject to all of the terms and provisions thereof. Optionee has
   reviewed the Plan and this Option in their entirety, has had an opportunity
   to obtain the advice of counsel prior to executing this Option and fully
   understands all provisions of the Option. Optionee hereby agrees to accept as
   binding, conclusive and final all decisions or interpretations of the
   Administrator upon any questions arising under the Plan or this Option.
   Optionee further agrees to notify the Company upon any change in the
   residence address indicated below.



        Dated:                                 ---------------------------------
               ------------------------        Optionee

                                               Residence Address:


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


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



                                       7.
<PAGE>   8
                                    EXHIBIT A

                                 1996 STOCK PLAN

                                 EXERCISE NOTICE

ViroLogic, Inc.
270 E. Grand Avenue
South San Francisco, CA 94080
Attention: Secretary

               1. EXERCISE OF OPTION. Effective as of today, _______, 20___, the
undersigned ("Optionee") hereby elects to exercise Optionee's option to purchase
________ shares of the Common Stock (the "Shares") of ViroLogic, Inc. (the
"Company") under and pursuant to the 1996 Stock Plan, as amended (the "Plan")
and the [ ] Incentive [X] Nonstatutory Stock Option Agreement dated ________,
20__ (the "Option Agreement").

               2. REPRESENTATIONS OF OPTIONEE. Optionee acknowledges that
Optionee has received, read and understood the Plan and the Option Agreement and
agrees to abide by and be bound by their terms and conditions.

               3. RIGHTS AS SHAREHOLDER. Until the stock certificate evidencing
such Shares is issued (as evidenced by the appropriate entry on the books of the
Company or of a duly authorized transfer agent of the Company), no right to vote
or receive dividends or any other rights as a shareholder shall exist with
respect to the Optioned Stock, notwithstanding the exercise of the Option. The
Company shall issue (or cause to be issued) such stock certificate promptly
after the Option is exercised. No adjustment will be made for a dividend or
other right for which the record date is prior to the date the stock certificate
is issued, except as provided in Section 12 of the Plan.

               Optionee shall enjoy rights as a shareholder until such time as
Optionee disposes of the Shares or the Company and/or its assignee(s) exercises
the Right of First Refusal hereunder. Upon such exercise, Optionee shall have no
further rights as a holder of the Shares so purchased except the right to
receive payment for the Shares so purchased in accordance with the provisions of
this Agreement, and Optionee shall forthwith cause the certificate(s) evidencing
the Shares so purchased to be surrendered to the Company for transfer or
cancellation.

               4. COMPANY'S RIGHT OF FIRST REFUSAL. Before any Shares held by
Optionee or any transferee (either being sometimes referred to herein as the
"Holder") may be sold or otherwise transferred (including transfer by gift or
operation of law), the Company or its assignee(s) shall have a right of first
refusal to purchase the Shares on the terms and conditions set forth in this
Section (the "Right of First Refusal").

                      a. NOTICE OF PROPOSED TRANSFER. The Holder of the Shares
shall deliver to the Company a written notice (the "Notice") stating: (i) the
Holder's bona fide intention to sell or otherwise transfer such Shares; (ii) the
name of each proposed purchaser or other transferee ("Proposed Transferee");
(iii) the number of Shares to be transferred to each Proposed Transferee; and
(iv) the bona fide cash price or other consideration for which the


<PAGE>   9
Holder proposes to transfer the Shares (the "Offered Price"), and the Holder
shall offer the Shares at the Offered Price to the Company or its assignee(s).

                      b. EXERCISE OF RIGHT OF FIRST REFUSAL. At any time within
thirty (30) days after receipt of the Notice, the Company and/or its assignee(s)
may, by giving written notice to the Holder, elect to purchase all, but not less
than all, of the Shares proposed to be transferred to any one or more of the
Proposed Transferees, at the purchase price determined in accordance with
subsection (c) below.

                      c. PURCHASE PRICE. The purchase price ("Purchase Price")
for the Shares purchased by the Company or its assignee(s) under this Section
shall be the Offered Price. If the Offered Price includes consideration other
than cash, the cash equivalent value of the non-cash consideration shall be
determined by the Board of Directors of the Company in good faith.

                      d. PAYMENT. Payment of the Purchase Price shall be made,
at the option of the Company or its assignee(s), in cash (by check), by
cancellation of all or a portion of any outstanding indebtedness of the Holder
to the Company (or, in the case of repurchase by an assignee, to the assignee),
or by any combination thereof within 30 days after receipt of the Notice or in
the manner and at the times set forth in the Notice.

                      e. HOLDER'S RIGHT TO TRANSFER. If all of the Shares
proposed in the Notice to be transferred to a given Proposed Transferee are not
purchased by the Company and/or its assignee(s) as provided in this Section,
then the Holder may sell or otherwise transfer such Shares to that Proposed
Transferee at the Offered Price or at a higher price, provided that such sale or
other transfer is consummated within 120 days after the date of the Notice and
provided further that any such sale or other transfer is effected in accordance
with any applicable securities laws and the Proposed Transferee agrees in
writing that the provisions of this Section shall continue to apply to the
Shares in the hands of such Proposed Transferee. If the Shares described in the
Notice are not transferred to the Proposed Transferee within such period, a new
Notice shall be given to the Company, and the Company and/or its assignees shall
again be offered the Right of First Refusal before any Shares held by the Holder
may be sold or otherwise transferred.

                      f. EXCEPTION FOR CERTAIN FAMILY TRANSFERS. Anything to the
contrary contained in this Section notwithstanding, the transfer of any or all
of the Shares during the Optionee's lifetime or on the Optionee's death by will
or intestacy to the Optionee's immediate family or a trust for the benefit of
the Optionee's immediate family shall be exempt from the provisions of this
Section. "Immediate Family" as used herein shall mean spouse, lineal descendant
or antecedent, father, mother, brother or sister. In such case, the transferee
or other recipient shall receive and hold the Shares so transferred subject to
the provisions of this Section, and there shall be no further transfer of such
Shares except in accordance with the terms of this Section.

                      g. TERMINATION OF RIGHT OF FIRST REFUSAL. The Right of
First Refusal shall terminate as to any Shares 90 days after the first sale of
Common Stock of the Company to the general public pursuant to a registration
statement filed with and declared



                                       2.
<PAGE>   10
effective by the Securities and Exchange Commission under the Securities Act of
1933, as amended.

               5. TAX CONSULTATION. Optionee understands that Optionee may
suffer adverse consequences as a result of Optionee's purchase or disposition of
the Shares. Optionee represents that Optionee has consulted with any tax
consultants Optionee deems advisable in connection with the purchase or
disposition of the Shares and that Optionee is not relying on the Company for
any tax advice.

               6. RESTRICTIVE LEGENDS AND STOP TRANSFER ORDERS.

                      a. LEGENDS. optionee understands and agrees that the
Company shall cause the legends set forth below or legends substantially
equivalent thereto, to be placed upon any certificate(s) evidencing ownership of
the Shares together with any other legends that may be required by the Company
or by state or federal securities laws:

               THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER
               THE SECURITIES ACT OF 1933 (THE "ACT") AND MAY NOT BE OFFERED,
               SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND
               UNTIL REGISTERED UNDER THE ACT OR, IN THE OPINION OF COUNSEL
               SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE
               OR TRANSFER, PLEDGE OR HYPOTHECATION IS IN COMPLIANCE THEREWITH.

               THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
               RESTRICTIONS ON TRANSFER AND A RIGHT OF FIRST REFUSAL HELD BY THE
               ISSUER OR ITS ASSIGNEE(S) AS SET FORTH IN THE EXERCISE NOTICE
               BETWEEN THE ISSUER AND THE ORIGINAL HOLDER OF THESE SHARES, A
               COPY OF WHICH MAY BE OBTAINED AT THE PRINCIPAL OFFICE OF THE
               ISSUER SUCH TRANSFER RESTRICTIONS AND RIGHT OF FIRST REFUSAL ARE
               BINDING ON TRANSFEREES OF THESE SHARES.

               IT IS UNLAWFUL TO CONSUMMATE A SALE OR TRANSFER OF THIS SECURITY,
               OR ANY INTEREST THEREIN, OR TO RECEIVE ANY CONSIDERATION
               THEREFOR, WITHOUT THE PRIOR WRITTEN CONSENT OF THE COMMISSIONER
               OF CORPORATIONS OF THE STATE OF CALIFORNIA, EXCEPT AS PERMITTED
               IN THE COMMISSIONERS RULES.

               Optionee understands that transfer of the Shares may be
restricted by Section 260.141.11 of the Rules of the California Corporations
Commissioner, a copy of which



                                       3.
<PAGE>   11
is attached to Exhibit B, the Investment Representation Statement.

                      b. STOP-TRANSFER NOTICES. Optionee agrees that, in order
to ensure compliance with the restrictions referred to herein, the Company may
issue appropriate "stop transfer" instructions to its transfer agent, if any,
and that, if the Company transfers its own securities, it may make appropriate
notations to the same effect in its own records.

                      c. REFUSAL TO TRANSFER. The Company shall not be required
(i) to transfer on its books any Shares that have been sold or otherwise
transferred in violation of any of the provisions of this Agreement or (ii) to
treat as owner of such Shares or to accord the right to vote or pay dividends to
any purchaser or other transferee to whom such Shares shall have been so
transferred.

               7. SUCCESSORS AND ASSIGNS. The Company may assign any of its
rights under this Agreement to single or multiple assignees, and this Agreement
shall inure to the benefit of the successors and assigns of the Company. Subject
to the restrictions on transfer herein set forth, this Agreement shall be
binding upon Optionee and his or her heirs, executors, administrators,
successors and assigns.

               8. INTERPRETATION. Any dispute regarding the interpretation of
this Agreement shall be submitted by Optionee or by the Company forthwith to the
Company's Board of Directors or the committee thereof that administers the Plan,
which shall review such dispute at its next regular meeting. The resolution of
such a dispute by the Board or committee shall be final and binding on the
Company and on Optionee.

               9. GOVERNING LAW; SEVERABILITY. This Agreement shall be governed
by and construed in accordance with the laws of the State of California
excluding that body of law pertaining to conflicts of law. Should any provision
of this Agreement be determined by a court of law to be illegal or
unenforceable, the other provisions shall nevertheless remain effective and
shall remain enforceable.

               10. NOTICE. Any notice required or permitted hereunder shall be
given in writing and shall be deemed effectively given upon personal delivery or
upon deposit in the United States mail by certified mail, with postage and fees
prepaid, addressed to the other party at its address as shown below beneath its
signature, or to such other address as such party may designate in writing from
time to time to the other party.

               11. FURTHER INSTRUMENTS. The parties agree to execute such
further instruments and to take such further action as may be reasonably
necessary to carry out the purposes and intent of this Agreement.

               12. DELIVERY OF PAYMENT. Optionee herewith delivers to the
Company the full Exercise Price for the Shares.

               13. ENTIRE AGREEMENT. The Plan and Notice of Grant/Option
Agreement are incorporated herein by reference. This Agreement, the Plan, the
Option Agreement and the Investment Representation Statement constitute the
entire agreement of the parties with respect to the subject matter hereof and
supersede in their entirety all prior undertakings and agreements



                                       4.
<PAGE>   12
of the Company and Purchaser with respect to the subject matter hereof, and may
not be modified adversely to the Purchaser's interest except by means of a
writing signed by the Company and Purchaser.



Submitted by:                               Accepted by:

OPTIONEE:                                   VIROLOGIC, INC.

                                            By:
                                               ---------------------------------
                                            Its:
                                                --------------------------------

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

Address:                                    Address:

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


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



                                       5.
<PAGE>   13
                      (TO BE COMPLETED AT TIME OF EXERCISE)

                                    EXHIBIT B

                       INVESTMENT REPRESENTATION STATEMENT

OPTIONEE:

Company:                     VIROLOGIC, INC.

SECURITY:                    COMMON STOCK

AMOUNT:

DATE:

In connection with the purchase of the above-listed Securities, the undersigned
Optionee represents to the Company the following:

                      a. Optionee is aware of the Company's business affairs and
financial condition and has acquired sufficient information about the Company to
reach an informed and knowledgeable decision to acquire the Securities. Optionee
is acquiring these Securities for investment for Optionee's own account only and
not with a view to, or for resale in connection with, any "distribution" thereof
within the meaning of the Securities Act of 1933, as amended (the "Securities
Act").

                      b. Optionee acknowledges and understands that the
Securities constitute "restricted securities" under the Securities Act and have
not been registered under the Securities Act in reliance upon a specific
exemption therefrom, which exemption depends upon, among other things, the bona
fide nature of Optionee's investment intent as expressed herein. In this
connection, Optionee understands that, in the view of the Securities and
Exchange Commission, the statutory basis for such exemption may be unavailable
if Optionee's representation was predicated solely upon a present intention to
hold these Securities for the minimum capital gains period specified under tax
statutes, for a deferred sale, for or until an increase or decrease in the
market price of the Securities, or for a period of one year or any other fixed
period in the future. Optionee further understands that the Securities must be
held indefinitely unless they are subsequently registered under the Securities
Act or an exemption from such registration is available. Optionee further
acknowledges and understands that the Company is under no obligation to register
the Securities. Optionee understands that the certificate evidencing the
Securities will be imprinted with a legend which prohibits the transfer of the
Securities unless they are registered or such registration is not required in
the opinion of counsel satisfactory to the Company, a legend prohibiting their
transfer without the consent of the Commissioner of Corporations of the State of
California and any other legend required under applicable state securities laws.

                      c. Optionee is familiar with the provisions of Rule 701
and Rule 144, each promulgated under the Securities Act, which, in substance,
permit limited public resale of "restricted securities" acquired, directly or
indirectly from the issuer thereof, in a nonpublic

<PAGE>   14
offering subject to the satisfaction of certain conditions. Rule 701 provides
that if the issuer qualifies under Rule 701 at the time of the grant of the
Option to the Optionee, the exercise will be exempt from registration under the
Securities Act. In the event the Company becomes subject to the reporting
requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934,
ninety (90) days thereafter (or such longer period as any market stand-off
agreement may require) the Securities exempt under Rule 701 may be resold,
subject to the satisfaction of certain of the conditions specified by Rule 144,
including: (1) the resale being made through a broker in an unsolicited
"broker's transaction" or in transactions directly with a market maker (as said
term is defined under the Securities Exchange Act of 1934); and, in the case of
an affiliate, (2) the availability of certain public information about the
Company, (3) the amount of Securities being sold during any three month period
not exceeding the limitations specified in Rule 144(e), and (4) the timely
filing of a Form 144, if applicable.

               In the event that the Company does not qualify under Rule 701 at
the time of grant of the Option, then the Securities may be resold in certain
limited circumstances subject to the provisions of Rule 144, which requires the
resale to occur not less than two years after the later of the date the
Securities were sold by the Company or the date the Securities were sold by an
affiliate of the Company, within the meaning of Rule 144; and, in the case of
acquisition of the Securities by an affiliate, or by a non-affiliate who
subsequently holds the Securities less than three years, the satisfaction of the
conditions set forth in sections (1), (2), (3) and (4) of the paragraph
immediately above.

                      d. Optionee hereby agrees that if so requested by the
Company or any representative of the underwriters in connection with any
registration of the offering of any securities of the Company under the
Securities Act, Optionee shall not sell or otherwise transfer any Shares or
other securities of the Company during the 180-day period following the
effective date of a registration statement of the Company filed under the
Securities Act; provided, however, that such restriction shall only apply to the
first registration statement of the Company to become effective under the
Securities Act which include securities to be sold on behalf of the Company to
the public in an underwritten public offering under the Securities Act. The
Company may impose stop-transfer instructions with respect to securities subject
to the foregoing restrictions until the end of such 180-day period.

                      e. Optionee further understands that in the event all of
the applicable requirements of Rule 701 or 144 are not satisfied, registration
under the Securities Act, compliance with Regulation A, or some other
registration exemption will be required; and that, notwithstanding the fact that
Rules 144 and 701 are not exclusive, the Staff of the Securities and Exchange
Commission has expressed its opinion that persons proposing to sell private
placement securities other than in a registered offering and otherwise than
pursuant to Rules 144 or 701 will have a substantial burden of proof in
establishing that an exemption from registration is available for such offers or
sales, and that such persons and their respective brokers who participate in
such transactions do so at their own risk. Optionee understands that no
assurances can be given that any such other registration exemption will be
available in such event.

                      f. Optionee understands that the certificate evidencing
the Securities will be imprinted with a legend which prohibits the transfer of
the Securities without the consent



                                       2.
<PAGE>   15
of the Commissioner of Corporations of California. Optionee has read the
applicable Commissioner's Rules with respect to such restriction, a copy of
which is attached.



                                               Signature of Optionee:


                                               ---------------------------------
                                               Date:                , 19
                                                      --------------    --


                                       3.
<PAGE>   16
                                  ATTACHMENT 1
              STATE OF CALIFORNIA - CALIFORNIA ADMINISTRATIVE CODE

         Title 10. Investment - Chapter 3. Commissioner of Corporations

  260.141.11: Restriction on Transfer. (a) The issuer of any security upon which
a restriction on transfer has been imposed pursuant to Sections 260.102.6,
260.141.10 or 260.534 shall cause a copy of this section to be delivered to each
issuee or transferee of such security at the time the certificate evidencing the
security is delivered to the issuee or transferee.

  (b) It is unlawful for the holder of any such security to consummate a sale or
transfer of such security, or any interest therein, without the prior written
consent of the Commissioner (until this condition is removed pursuant to Section
260.141.12 of these rules), except:

        (1) to the issuer;

        (2) pursuant to the order or process of any court;

        (3) to any person described in Subdivision (i) of Section 25102 of the
Code or Section 260.105.14 of these rules;

        (4) to the transferor's ancestors, descendants or spouse, or any
custodian or trustee for the account of the transferor or the transferor's
ancestors, descendants, or spouse; or to a transferee by a trustee or custodian
for the account of the transferee or the transferee's ancestors, descendants or
spouse;

        (5) to holders of securities of the same class of the same issuer;

        (6) by way of gift or donation inter vivos or on death;

        (7) by or through a broker-dealer licensed under the Code (either acting
as such or as a finder) to a resident of a foreign state, territory or country
who is neither domiciled in this state to the knowledge of the broker-dealer,
nor actually present in this state if the sale of such securities is not in
violation of any securities law of the foreign state, territory or country
concerned;

        (8) to a broker-dealer licensed under the Code in a principal
transaction, or as an underwriter or member of an underwriting syndicate or
selling group;

        (9) if the interest sold or transferred is a pledge or other lien given
by the purchaser to the seller upon a sale of the security for which the
Commissioner's written consent is obtained or under this rule not required;

        (10) by way of a sale qualified under Sections 25111, 25112, 25113 or
25121 of the Code, of the securities to be transferred, provided that no order
under Section 25140 or subdivision (a) of Section 25143 is in effect with
respect to such qualification;

        (11) by a corporation to a wholly owned subsidiary of such corporation,
or by a wholly owned subsidiary of a corporation to such corporation;

        (12) by way of an exchange qualified under Section 25111, 25112 or 25113
of the Code, provided that no order under Section 25140 or subdivision (a) of
Section 25143 is in effect with respect to such qualification;

        (13) between residents of foreign states, territories or countries who
are neither domiciled nor actually present in this state;

        (14) to the State Controller pursuant to the Unclaimed Property Law or
to the administrator of the unclaimed property law of another state; or

        (15) by the State Controller pursuant to the Unclaimed Property Law or
by the administrator of the unclaimed property law of another state if, in
either such case, such person (i) discloses to potential purchasers at the sale
that transfer of the securities is restricted under this rule, (ii) delivers to
each purchaser a copy of this rule, and (iii) advises the Commissioner of the
name of each purchaser;

        (16) by a trustee to a successor trustee when such transfer does not
involve a change in the beneficial ownership of the securities;

        (17) by way of an offer and sale of outstanding securities in an issuer
transaction that is subject to the qualification requirement of Section 25110 of
the Code but exempt from that qualification requirement by subdivision (f) of
Section 25102; provided that any such transfer is on the condition that any
certificate evidencing the security issued to such transferee shall contain the
legend required by this section.

        (c) The certificates representing all such securities subject to such a
restriction on transfer, whether upon initial issuance or upon any transfer
thereof, shall bear on their face a legend, prominently stamped or printed
thereon in capital letters of not less than 10-point size, reading as follows:

      "IT IS UNLAWFUL TO CONSUMMATE A SALE OR TRANSFER OF THIS SECURITY, OR ANY
      INTEREST THEREIN, OR TO RECEIVE ANY CONSIDERATION THEREFOR, WITHOUT THE
      PRIOR WRITTEN CONSENT OF THE COMMISSIONER OF CORPORATIONS OF THE STATE OF
      CALIFORNIA EXCEPT AS PERMITTED IN THE COMMISSIONER'S RULES."