<PAGE>
                                                                    EXHIBIT 4.10


THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"). THEY MAY NOT BE SOLD, OFFERED
FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
STATEMENT AS TO SUCH SECURITIES UNDER THE ACT OR AN OPINION OF COUNSEL
SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

                                 VIROLOGIC, INC.

                        WARRANT TO PURCHASE COMMON STOCK

NO. W-12                                                      SEPTEMBER 27, 2001
                          VOID AFTER SEPTEMBER 27, 2006

THIS CERTIFIES THAT, for value received, Aspen Capital Partners, Inc., with its
principal office at 11693 San Vicente Boulevard, No. 226, Los Angeles,
California 90049, or assigns (the "HOLDER"), is entitled to subscribe for and
purchase at the Exercise Price (defined below) from VIROLOGIC, INC., a DELAWARE
corporation, with its principal office at 270 East Grand Avenue, South San
Francisco, California 94080 (the "COMPANY") up to 18,200 shares of the Common
Stock of the Company (the "COMMON STOCK").

         1.       DEFINITIONS. As used herein, the following terms shall have
the following respective meanings:

                  (a)      "EXERCISE PERIOD" shall mean the period commencing
with the date hereof and ending five years from the date hereof, unless sooner
terminated as provided below.

                  (b)      "EXERCISE PRICE" shall mean $2.178 per share, subject
to adjustment pursuant to Section 5 below.

                  (c)      "EXERCISE SHARES" shall mean the shares of the
Company's Common Stock issuable upon exercise of this Warrant.

         2.       EXERCISE OF WARRANT. The rights represented by this Warrant
may be exercised in whole or in part at any time during the Exercise Period, by
delivery of the following to the Company at its address set forth above (or at
such other address as it may designate by notice in writing to the Holder):

                  (a)      An executed Notice of Exercise in the form attached
hereto;

                  (b)      Payment of the Exercise Price either (i) in cash or
by check, or (ii) by cancellation of indebtedness; and

                  (c)      This Warrant.

                  Upon the exercise of the rights represented by this Warrant, a
certificate or certificates for the Exercise Shares so purchased, registered in
the name of the Holder or persons affiliated with


                                       1.
<PAGE>
the Holder, if the Holder so designates, shall be issued and delivered to the
Holder within a reasonable time after the rights represented by this Warrant
shall have been so exercised.

                  The person in whose name any certificate or certificates for
Exercise Shares are to be issued upon exercise of this Warrant shall be deemed
to have become the holder of record of such shares on the date on which this
Warrant was surrendered and payment of the Exercise Price was made, irrespective
of the date of delivery of such certificate or certificates, except that, if the
date of such surrender and payment is a date when the stock transfer books of
the Company are closed, such person shall be deemed to have become the holder of
such shares at the close of business on the next succeeding date on which the
stock transfer books are open.

         2.1      CASHLESS EXERCISE. Notwithstanding any provisions herein to
the contrary, if the fair market value of one share of the Company's Common
Stock is greater than the Exercise Price (at the date of calculation as set
forth below), in lieu of exercising this Warrant by payment of cash, the Holder
may elect to receive shares equal to the value (as determined below) of this
Warrant (or the portion thereof being canceled) by surrender of this Warrant at
the principal office of the Company together with the properly endorsed Notice
of Exercise in which event the Company shall issue to the Holder a number of
shares of Common Stock computed using the following formula:

                           X = Y (A-B)
                               -------
                                  A

         Where X =   the number of shares of Common Stock to be issued to the
                     Holder

               Y =   the number of shares of Common Stock purchasable under the
                     Warrant or, if only a portion of the Warrant is being
                     exercised, the portion of the Warrant being canceled (at
                     the date of such calculation)

               A =   the fair market value of one share of the Company's Common
                     Stock (at the date of such calculation)

               B =   Exercise Price (as adjusted to the date of such
                     calculation)

         For purposes of the above calculation, the fair market value of one
share of Common Stock shall be equal to the closing sales price of the Company's
Common Stock as reported on the NASDAQ National Market on the trading day
immediately preceding the date of calculation.

         3.       COVENANTS OF THE COMPANY.

         3.1      COVENANTS AS TO EXERCISE SHARES. The Company covenants and
agrees that all Exercise Shares that may be issued upon the exercise of the
rights represented by this Warrant will, upon issuance, be validly issued and
outstanding, fully paid and nonassessable, and free from all taxes, liens and
charges with respect to the issuance thereof. The Company further covenants and
agrees that the Company will at all times during the Exercise Period, have
authorized and reserved, free from preemptive rights, a sufficient number of
shares of its Common Stock to provide for the exercise of the rights represented
by this Warrant. If at any time during the Exercise Period the number of
authorized but unissued shares of Common Stock


                                       2.
<PAGE>
shall not be sufficient to permit exercise of this Warrant, the Company will
take such corporate action as may, in the opinion of its counsel, be necessary
to increase its authorized but unissued shares of Common Stock to such number of
shares as shall be sufficient for such purposes.

         3.2      NO IMPAIRMENT. Except and to the extent as waived or consented
to by the Holder, the Company will not, by amendment of its Certificate of
Incorporation or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms to be
observed or performed hereunder by the Company, but will at all times in good
faith assist in the carrying out of all the provisions of this Warrant and in
the taking of all such action as may be necessary or appropriate in order to
protect the exercise rights of the Holder against impairment.

         3.3      NOTICES OF RECORD DATE. In the event of any taking by the
Company of a record of the holders of any class of securities for the purpose of
determining the holders thereof who are entitled to receive any dividend (other
than a cash dividend which is the same as cash dividends paid in previous
quarters) or other distribution, the Company shall mail to the Holder, at least
ten (10) days prior to the date specified herein, a notice specifying the date
on which any such record is to be taken for the purpose of such dividend or
distribution.

         4.       REPRESENTATIONS OF HOLDER.

         4.1      ACQUISITION OF WARRANT FOR PERSONAL ACCOUNT. The Holder
represents and warrants that it is acquiring the Warrant solely for its account
for investment and not with a view to or for sale or distribution of said
Warrant or any part thereof. The Holder also represents that the entire legal
and beneficial interests of the Warrant and Exercise Shares the Holder is
acquiring is being acquired for, and will be held for, its account only.

         4.2      SECURITIES ARE NOT REGISTERED.

                  (a)      The Holder understands that the Warrant and the
Exercise Shares have not been registered under the Securities Act of 1933, as
amended (the "ACT") on the basis that no distribution or public offering of the
stock of the Company is to be effected. The Holder realizes that the basis for
the exemption may not be present if, notwithstanding its representations, the
Holder has a present intention of acquiring the securities for a fixed or
determinable period in the future, selling (in connection with a distribution or
otherwise), granting any participation in, or otherwise distributing the
securities. The Holder has no such present intention.

                  (b)      The Holder recognizes that the Warrant and the
Exercise Shares must be held indefinitely unless they are subsequently
registered under the Act or an exemption from such registration is available.
The Holder recognizes that the Company has no obligation to register the Warrant
or the Exercise Shares of the Company, or to comply with any exemption from such
registration.

                  (c)      The Holder is aware that neither the Warrant nor the
Exercise Shares may be sold pursuant to Rule 144 adopted under the Act unless
certain conditions are met, including, among other things, the existence of a
public market for the shares, the availability of certain current public
information about the Company, the resale following the required holding period


                                       3.
<PAGE>
under Rule 144 and the number of shares being sold during any three month period
not exceeding specified limitations. Holder is aware that the conditions for
resale set forth in Rule 144 have not been satisfied and that the Company
presently has no plans to satisfy these conditions in the foreseeable future.

         4.3      DISPOSITION OF WARRANT AND EXERCISE SHARES.

                  (a)      The Holder further agrees not to make any disposition
of all or any part of the Warrant or Exercise Shares in any event unless and
until:

                           (i)      The Company shall have received a letter
secured by the Holder from the Securities and Exchange Commission stating that
no action will be recommended to the Commission with respect to the proposed
disposition; or

                           (ii)     There is then in effect a registration
statement under the Act covering such proposed disposition and such disposition
is made in accordance with said registration statement; or

                           (iii)    The Holder shall have notified the Company
of the proposed disposition and shall have furnished the Company with a detailed
statement of the circumstances surrounding the proposed disposition, and if
reasonably requested by the Company, the Holder shall have furnished the Company
with an opinion of counsel, reasonably satisfactory to the Company, for the
Holder to the effect that such disposition will not require registration of such
Warrant or Exercise Shares under the Act or any applicable state securities
laws.

                  (b)      The Holder understands and agrees that all
certificates evidencing the shares to be issued to the Holder may bear the
following legend:

         THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
         1933, AS AMENDED (THE "ACT"). THEY MAY NOT BE SOLD, OFFERED FOR SALE,
         PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
         STATEMENT AS TO THE SECURITIES UNDER THE ACT OR AN OPINION OF COUNSEL
         SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

         5.       ADJUSTMENT OF EXERCISE PRICE. In the event of changes in the
outstanding Common Stock of the Company by reason of stock dividends, split-ups,
recapitalizations, reclassifications, combinations or exchanges of shares,
separations, reorganizations, liquidations, or the like, the number and class of
shares available under the Warrant in the aggregate and the Exercise Price shall
be correspondingly adjusted to give the Holder of the Warrant, on exercise for
the same aggregate Exercise Price, the total number, class, and kind of shares
as the Holder would have owned had the Warrant been exercised prior to the event
and had the Holder continued to hold such shares until after the event requiring
adjustment; provided, however, that such adjustment shall not be made with
respect to, and this Warrant shall terminate if not exercised prior to, the
events set forth in Section 7 below. The form of this Warrant need not be
changed because of any adjustment in the number of Exercise Shares subject to
this Warrant.


                                       4.
<PAGE>
         6.       FRACTIONAL SHARES. No fractional shares shall be issued upon
the exercise of this Warrant as a consequence of any adjustment pursuant hereto.
All Exercise Shares (including fractions) issuable upon exercise of this Warrant
may be aggregated for purposes of determining whether the exercise would result
in the issuance of any fractional share. If, after aggregation, the exercise
would result in the issuance of a fractional share, the Company shall, in lieu
of issuance of any fractional share, pay the Holder otherwise entitled to such
fraction a sum in cash equal to the product resulting from multiplying the then
current fair market value of an Exercise Share by such fraction.

         7.       EARLY TERMINATION. In the event of, at any time during the
Exercise Period, any capital reorganization, or any reclassification of the
capital stock of the Company (other than a change in par value or from par value
to no par value or no par value to par value or as a result of a stock dividend
or subdivision, split-up or combination of shares), or the consolidation or
merger of the Company with or into another corporation (other than a merger
solely to effect a reincorporation of the Company into another state), or the
sale or other disposition of all or substantially all the properties and assets
of the Company in its entirety to any other person, the Company shall provide to
the Holder twenty (20) days advance written notice of such public offering,
reorganization, reclassification, consolidation, merger or sale or other
disposition of the Company's assets, and this Warrant shall terminate unless
exercised prior to the occurrence of such reorganization, reclassification,
consolidation, merger or sale or other disposition of the Company's assets.

         8.       MARKET STAND-OFF AGREEMENT. Holder shall not sell, dispose of,
transfer, make any short sale of, grant any option for the purchase of, or enter
into any hedging or similar transaction with the same economic effect as a sale,
any Common Stock (or other securities) of the Company held by Holder, for a
period of time specified by the managing underwriter(s) or reasonably determined
by the Company (not to exceed one hundred eighty (180 days) following the
effective date of a registration statement of the Company filed under the Act.
Holder agrees to execute and deliver such other agreements as may be reasonably
requested by the Company and/or the managing underwriter(s) which are consistent
with the foregoing or which are necessary to give further effect thereto. In
order to enforce the foregoing covenant, the Company may impose stop-transfer
instructions with respect to such Common Stock (or other securities) until the
end of such period. The underwriters of the Company's stock are intended third
party beneficiaries of this Section 8 and shall have the right, power and
authority to enforce the provisions hereof as though they were a party hereto.

         9.       NO STOCKHOLDER RIGHTS. This Warrant in and of itself shall not
entitle the Holder to any voting rights or other rights as a stockholder of the
Company.

         10.      TRANSFER OF WARRANT. Subject to applicable laws and the
restriction on transfer set forth on the first page of this Warrant, this
Warrant and all rights hereunder are transferable, by the Holder in person or by
duly authorized attorney, upon delivery of this Warrant and the form of
assignment attached hereto to any transferee designated by Holder. The
transferee shall sign an investment letter in form and substance satisfactory to
the Company.

         11.      LOST, STOLEN, MUTILATED OR DESTROYED WARRANT. If this Warrant
is lost, stolen, mutilated or destroyed, the Company may, on such terms as to
indemnity or otherwise as


                                       5.
<PAGE>
it may reasonably impose (which shall, in the case of a mutilated Warrant,
include the surrender thereof), issue a new Warrant of like denomination and
tenor as the Warrant so lost, stolen, mutilated or destroyed. Any such new
Warrant shall constitute an original contractual obligation of the Company,
whether or not the allegedly lost, stolen, mutilated or destroyed Warrant shall
be at any time enforceable by anyone.

         12.      NOTICES, ETC. All notices required or permitted hereunder
shall be in writing and shall be deemed effectively given: (a) upon personal
delivery to the party to be notified, (b) when sent by confirmed telex or
facsimile if sent during normal business hours of the recipient, if not, then on
the next business day, (c) five (5) days after having been sent by registered or
certified mail, return receipt requested, postage prepaid, or (d) one (1) day
after deposit with a nationally recognized overnight courier, specifying next
day delivery, with written verification of receipt. All communications shall be
sent to the Company or to Holder at their respective addresses listed on the
first page hereof or at such other address as the Company or Holder may
designate by ten (10) days advance written notice to the other parties hereto.

         13.      REGISTRATION RIGHTS.

         13.1     PIGGY-BACK REGISTRATION. If the Company shall determine to
register any of its securities either for its own account or the account of
other security holders (other than a registration relating solely to employee
benefit plans, or a registration relating solely to a Rule 145 transaction, or a
registration on any registration form that does not permit secondary sales, or
any registration made in connection with the sale by the Company to certain
investors of its Series A Convertible Preferred Stock) the Company will (X)
promptly give to the Holder written notice thereof and (Y) use its best efforts
to include in such registration (and any related qualification under blue sky
laws or other compliance), except as set forth in Section 13.2 below, and in any
underwriting involved therein, all the Exercise Shares specified in a written
request or requests, made by the Holder and received by the Company within
twenty (20) days after the written notice from the Company described in clause
(i) above is mailed or delivered by the Company. Such written request may
specify all or a part of the Holder's Exercise Shares.

         13.2     UNDERWRITING.

                  (a)      If the registration of which the Company gives notice
is for a registered public offering involving an underwriting, the Company shall
so advise the Holder as a part of the written notice given pursuant to Section
13.1. In such event, the right of the Holder to registration pursuant to this
Section 13 shall be conditioned upon the Holder's participation in such
underwriting and the inclusion of such Holder's Exercise Shares in the
underwriting to the extent provided herein. The Holders shall (together with the
Company and the other holders of securities of the Company with registration
rights to participate therein distributing their securities through such
underwriting) enter into an underwriting agreement in customary form with the
representative of the underwriter or underwriters selected by the Company.

                  (b)      Notwithstanding any other provision of this Section
13, if the representative of the underwriters advises the Company in writing
that marketing factors require a limitation on the number of shares to be
underwritten, the representative may (subject to the limitations set forth
below) exclude all Exercise Shares from, or limit the number of Exercise Shares
to be


                                       6.
<PAGE>
included in, the registration and underwriting. The Company may limit, to the
extent so advised by the underwriters, the amount of securities to be included
in the registration by the Company's stockholders (including the Holder);
provided, however, that any such limitation or cutback shall first be applied to
(i) shares proposed to be sold in such offering other than for the account of
the Company which are not Exercise Shares and not subject to a written agreement
with the Company pursuant to which the Company would be contractually bound to
register such shares (subject to relevant cutback provisions), then to (ii) the
Exercise Shares, then to (iii) shares proposed to be sold in such offering other
than for the account or the Company which are not Exercise Shares and which are
subject to a written agreement with the Company pursuant to which the Company is
contractually bound to register such shares (subject to relevant cutback
provisions). The Company shall so advise all holders of securities requesting
registration, and the number of shares of securities that are entitled to be
included in the registration and underwriting shall be allocated first to the
Company for securities being sold for its own account and thereafter as set
forth in Section 13.8 and as set forth in the previous sentence. If any person
does not agree to the terms of any such underwriting, he shall be excluded
therefrom by written notice from the Company or the underwriter. Any Exercise
Shares or other securities excluded or withdrawn from such underwriting shall be
withdrawn from such registration.

                  (c)      If shares are so withdrawn from the registration and
if the number of Exercise Shares to be included in such registration was
previously reduced as a result of marketing factors, the Company shall then
offer to all persons who have retained the right to include securities in the
registration the right to include additional securities in the registration in
an aggregate amount equal to the number of shares so withdrawn, with such shares
to be allocated among the persons requesting additional inclusion in accordance
with Section 13.8 hereof.

         13.3     EXPENSES OF REGISTRATION. All expenses incurred in connection
with any registration, qualification or compliance pursuant to this Section 13
shall be borne by the Company. All underwriting discounts and selling
commissions relating to Exercise Shares so registered shall be borne by the
Holder pro rata on the basis of the number of shares of Exercise Shares so
registered on its behalf.

         13.4     REGISTRATION PROCEDURES. In the case of each registration
effected by the Company pursuant to Section 13, the Company will keep the Holder
advised in writing as to the initiation of each registration and as to the
completion thereof. At its expense, the Company will use its best efforts to:

                  (a)      Keep (i) a registration on Form S-1 effective for a
period of ninety days or until the Holder has completed the distribution
described in the registration statement relating thereto, whichever first occurs
and (ii) a registration on Form S-3 effective for a period of 180 days or until
the Holder has completed the distribution described in the registration
statement related thereto, whichever first occurs (each an "EFFECTIVENESS
PERIOD"); provided, however, that the Effectiveness Period shall be extended for
a period of time equal to the period the Holder refrains from selling any
securities included in such registration at the request of the Company or of an
underwriter of Common Stock (or other securities) of the Company.

                  (b)      Prepare and file with the Securities and Exchange
Commission such amendments and supplements to such registration statement and
the prospectus used in


                                       7.
<PAGE>
connection with such registration statement as may be necessary to comply with
the provisions of the Act with respect to the disposition of all securities
covered by such registration statement;

                  (c)      Furnish such number of prospectuses and other
documents incident thereto, including any amendment of or supplement to the
prospectus, as the Holder from time to time may reasonably request;

                  (d)      Notify the Holder, at any time when a prospectus
relating to the Exercise Shares is required to be delivered under the Act, of
the happening of any event as a result of which the prospectus included in such
registration statement, as then in effect, includes an untrue statement of a
material fact or omits to state a material fact required to be stated therein or
necessary to make the statements therein not misleading or incomplete in the
light of the circumstances then existing, and at the request of any such seller,
prepare and furnish to such seller a reasonable number of copies of a supplement
to or an amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such shares, such prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading or
incomplete in the light of the circumstances then existing;

                  (e)      Cause all such Exercise Shares registered pursuant
hereunder to be listed on each securities exchange on which similar securities
issued by the Company are then listed;

                  (f)      Provide a transfer agent and registrar for all
Exercise Shares registered pursuant to such registration statement and a CUSIP
number for all such Exercise Shares, in each case not later than the effective
date of such registration;

                  (g)      Otherwise use its best efforts to comply with all
applicable rules and regulations of the Commission, and make available to its
security holders, as soon as reasonably practicable, an earnings statement
covering the period of at least twelve months, but not more than eighteen
months, beginning with the first month after the effective date of the
Registration Statement, which earnings statement shall satisfy the provisions of
Section 11(a) of the Act; and

         13.5     INDEMNIFICATION.

                  (a)      The Company will indemnify the Holder, each of its
officers, directors and partners, legal counsel, and accountants and each person
controlling the Holder within the meaning of Section 15 of the Act, with respect
to which registration, qualification, or compliance has been effected pursuant
to this Section 13, and each underwriter, if any, and each person who controls
within the meaning of Section 15 of the Act any underwriter, against all
expenses, claims, losses, damages, and liabilities (or actions, proceedings, or
settlements in respect thereof) arising out of or based on any untrue statement
(or alleged untrue statement) of a material fact contained in any prospectus,
offering circular, or other document (including any related registration
statement, notification, or the like) incident to any such registration,
qualification, or compliance with this Section 13, or based on any omission (or
alleged omission) to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading, or any violation by
the Company of the Act or any rule or regulation thereunder applicable to the
Company and relating to action or inaction required of the Company in


                                       8.
<PAGE>
connection with any such registration, qualification, or compliance, and will
reimburse the Holder, each of its officers, directors, partners, legal counsel,
and accountants and each person controlling the Holder, each such underwriter,
and each person who controls any such underwriter, for any legal and any other
expenses reasonably incurred in connection with investigating and defending or
settling any such claim, loss, damage, liability, or action, provided that the
Company will not be liable in any such case to the extent that any such claim,
loss, damage, liability, or expense arises out of or is based on any untrue
statement or omission based upon written information furnished to the Company by
the Holder or underwriter and stated to be specifically for use therein; unless
such information was subsequently corrected in a writing specifically noting the
correction furnished to the Company prior to the filing of the registration
statement. It is agreed that the indemnity agreement contained in this Section
13.5(a) shall not apply to amounts paid in settlement of any such loss, claim,
damage, liability, or action if such settlement is effected without the consent
of the Company (which consent has not been unreasonably withheld).

                  (b)      The Holder will, if Exercise Shares held by it are
included in the securities as to which such registration, qualification, or
compliance is being effected, indemnify the Company, each of its directors,
officers, partners, legal counsel, and accountants and each underwriter, if any,
of the Company's securities covered by such a registration statement, each
person who controls the Company or such underwriter within the meaning of
Section 15 of the Act, each other stockholder holding securities registered
thereon, and each of their officers, directors, and partners, and each person
controlling such other stockholder, against all claims, losses, damages and
liabilities (or actions in respect thereof) arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any such registration statement, prospectus, offering circular, or other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, and will reimburse the Company and the other stockholders,
directors, officers, partners, legal counsel, and accountants, persons,
underwriters, or control persons for any legal or any other expenses reasonably
incurred in connection with investigating or defending any such claim, loss,
damage, liability, or action, in each case to the extent, but only to the
extent, that such untrue statement (or alleged untrue statement) or omission (or
alleged omission) is made in such registration statement, prospectus, offering
circular, or other document in reliance upon and in conformity with written
information furnished to the Company by the Holder and stated to be specifically
for use therein provided, however, that the obligations of the Holder hereunder
shall not apply to amounts paid in settlement of any such claims, losses,
damages, or liabilities (or actions in respect thereof) if such settlement is
effected without the consent of the Holder (which consent shall not be
unreasonably withheld).

                  (c)      Each party entitled to indemnification under this
Section 13.5 (the "INDEMNIFIED PARTY") shall give notice to the party required
to provide indemnification (the "INDEMNIFYING PARTY") promptly after such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought, and shall permit the Indemnifying Party to assume the defense of such
claim or any litigation resulting therefrom, provided that counsel for the
Indemnifying Party, who shall conduct the defense of such claim or any
litigation resulting therefrom, shall be approved by the Indemnified Party
(whose approval shall not unreasonably be withheld), and the Indemnified Party
may participate in such defense at such party's expense,


                                       9.
<PAGE>
and provided further that the failure of any Indemnified Party to give notice as
provided herein shall not relieve the Indemnifying Party of its obligations
under this Section 13.5, to the extent such failure is not prejudicial. No
Indemnifying Party, in the defense of any such claim or litigation, shall,
except with the consent of each Indemnified Party, consent to entry of any
judgment or enter into any settlement that does not include as an unconditional
term thereof the giving by the claimant or plaintiff to such Indemnified Party
of a release from all liability in respect to such claim or litigation. Each
Indemnified Party shall furnish such information regarding itself or the claim
in question as an Indemnifying Party may reasonably request in writing and as
shall be reasonably required in connection with defense of such claim and
litigation resulting therefrom.

                  (d)      If the indemnification provided for in this Section
13.5 is held by a court of competent jurisdiction to be unavailable to an
Indemnified Party with respect to any loss, liability, claim, damage, or expense
referred to therein, then the Indemnifying Party, in lieu of indemnifying such
Indemnified Party hereunder, shall contribute to the amount paid or payable by
such Indemnified Party as a result of such loss, liability, claim, damage, or
expense in such proportion as is appropriate to reflect the relative fault of
the Indemnifying Party on the one hand and of the Indemnified Party on the other
in connection with the statements or omissions that resulted in such loss,
liability, claim, damage, or expense as well as any other relevant equitable
considerations. The relative fault of the Indemnifying Party and of the
Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission to state a material fact relates to information supplied by the
Indemnifying Party or by the Indemnified Party and the parties' relative intent,
knowledge, access to information, and opportunity to correct or prevent such
statement or omission.

                  (e)      Notwithstanding the foregoing, to the extent that the
provisions on indemnification and contribution contained in the underwriting
agreement entered into in connection with the underwritten public offering are
in conflict with the foregoing provisions, the provisions in the underwriting
agreement shall control.

         13.6     INFORMATION BY HOLDER. The Holder shall furnish to the Company
such information regarding the Holder and the distribution proposed by the
Holder as the Company may reasonably request in writing and as shall be
reasonably required in connection with any registration, qualification, or
compliance referred to in this Section 13.

         13.7     TRANSFER OR ASSIGNMENT OF REGISTRATION RIGHTS. The rights to
cause the Company to register securities granted to the Holder by the Company
under this Section 13 may be transferred or assigned by a Holder only to a
transferee or assignee of all of the Exercise Shares (as presently constituted
and subject to subsequent adjustments for stock splits, stock dividends, reverse
stock splits, and the like), provided that the Company is given written notice
at the time of or within a reasonable time after such transfer or assignment,
stating the name and address of the transferee or assignee and identifying the
securities with respect to which such registration rights are being transferred
or assigned, and, provided further, that the transferee or assignee of such
rights assumes in writing the obligations of such Holder under this Section 13.


                                      10.
<PAGE>
         13.8     ALLOCATION OF REGISTRATION OPPORTUNITIES. In any circumstance
in which all of the Exercise Shares, and other shares of Common Stock of the
Company (including shares of Common Stock issued or issuable upon conversion of
shares of any currently issued or unissued series of Preferred Stock of the
Company or upon exercise or conversion of any rights to purchase the Common
Stock of the Company) with registration rights pursuant to a written agreement
with the Company (the "OTHER SHARES"), requested to be included in a
registration on behalf of the Holder or other selling stockholders cannot be so
included as a result of limitations of the aggregate number of shares of
Exercise Shares and Other Shares that may be so included, the number of shares
of Exercise Shares and Other Shares that may be so included shall be allocated
among the Holder and other selling stockholders requesting inclusion of shares
first to such other stockholders and then to the Holder, as further described in
Section 13.2(b).

         13.9     DELAY OF REGISTRATION. The Holder shall not have any right to
take any action to restrain, enjoin, or otherwise delay any registration as the
result of any controversy that might arise with respect to the interpretation or
implementation of this Section 13.

         13.10    TERMINATION. This Section 13 shall terminate immediately
following the expiration of the Exercise Period or earlier if the Holder can
sell all of the Exercise Shares in a 90-day period pursuant to Rule 144.

         14.      ACCEPTANCE. Receipt of this Warrant by the Holder shall
constitute acceptance of and agreement to all of the terms and conditions
contained herein.

         15.      GOVERNING LAW. This Warrant and all rights, obligations and
liabilities hereunder shall be governed by the laws of the State of California.

         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer as of September 27, 2001.

                                   VIROLOGIC, INC.

                                   By: /s/ WILLIAM D. YOUNG
                                      ------------------------------------------

                                   Name: William D. Young
                                        ----------------------------------------

                                   Title: Chief Executive Officer
                                         ---------------------------------------


                                      11.
<PAGE>
                               NOTICE OF EXERCISE

TO:  VIROLOGIC, INC.

         (1)      [ ]      The undersigned hereby elects to purchase ________
shares of the Common Stock of ViroLogic, Inc. (the "Company") pursuant to the
terms of the attached Warrant, and tenders herewith payment of the exercise
price in full, together with all applicable transfer taxes, if any.

                  [ ]      The undersigned hereby elects to purchase ________
shares of the Common Stock of ViroLogic, Inc. (the "Company") pursuant to the
terms of the net exercise provisions set forth in Section 2.1 of the attached
Warrant, and shall tender payment of all applicable transfer taxes, if any.

         (2)      Please issue a certificate or certificates representing said
shares of Common Stock in the name of the undersigned or in such other name as
is specified below:


                            ------------------------
                                     (Name)


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

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

         (3)      The undersigned represents that (i) the aforesaid shares of
Common Stock are being acquired for the account of the undersigned for
investment and not with a view to, or for resale in connection with, the
distribution thereof and that the undersigned has no present intention of
distributing or reselling such shares; (ii) the undersigned 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
regarding its investment in the Company; (iii) the undersigned is experienced in
making investments of this type and has such knowledge and background in
financial and business matters that the undersigned is capable of evaluating the
merits and risks of this investment and protecting the undersigned's own
interests; (iv) the undersigned understands that the shares of Common Stock
issuable upon exercise of this Warrant have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), by reason of a
specific exemption from the registration provisions of the Securities Act, which
exemption depends upon, among other things, the bona fide nature of the
investment intent as expressed herein, and, because such securities have not
been registered under the Securities Act, they must be held indefinitely unless
subsequently registered under the Securities Act or an exemption from such
registration is available; (v) the undersigned is aware that the aforesaid
shares of Common Stock may not be sold pursuant to Rule 144 adopted under the
Securities Act unless certain conditions are met and until the undersigned has
held the shares for the number of years prescribed by Rule 144, that among the
conditions for use of the Rule is the availability of current information to the
public about the Company and the Company has not made such information available
and has no present plans to do so; and (vi) the undersigned agrees not to make
any disposition of all or any part of the aforesaid shares of Common Stock
unless and until there is then in effect a registration statement under the
Securities Act covering such proposed disposition and such disposition is made
in accordance with said registration

<PAGE>
statement, or the undersigned has provided the Company with an opinion of
counsel satisfactory to the Company, stating that such registration is not
required.


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


                                          --------------------------------------
                                          (Print name)
<PAGE>
                                 ASSIGNMENT FORM

                  (To assign the foregoing Warrant, execute
                  this form and supply required information.
                  Do not use this form to purchase shares.)

         FOR VALUE RECEIVED, the foregoing Warrant and all rights evidenced
thereby are hereby assigned to

Name:
       -------------------------------------------------------------------------
                                 (Please Print)

Address:
          ----------------------------------------------------------------------
                                 (Please Print)

Dated:            , 20
        ----------    --

Holder's
Signature:
            -----------------------------------------

Holder's
Address:
          -------------------------------------------



NOTE: The signature to this Assignment Form must correspond with the name as it
appears on the face of the Warrant, without alteration or enlargement or any
change whatever. Officers of corporations and those acting in a fiduciary or
other representative capacity should file proper evidence of authority to assign
the foregoing Warrant.