<PAGE>
                                                                     EXHIBIT 4.9


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-11                                                            JULY 2, 2001

                             VOID AFTER JULY 2, 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 11,800 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 $2.66 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 July 2, 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.