<PAGE>
                                                                   EXHIBIT 4.11


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-13                                                          MARCH 19, 2002
                            VOID AFTER MARCH 19, 2007

         THIS CERTIFIES THAT, for value received, CIBC World Markets Corp., with
its principal office at 425 Lexington Avenue, New York NY 10017, 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 100,000 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 $2.28 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.

         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.

         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


                                       4.
<PAGE>
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 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,


                                       5.
<PAGE>
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. The Company agrees to include the
Exercise Shares in the registration statement to be filed by the Company in
connection with the issuance of its Series B Convertible Preferred Stock,
subject to the terms and obligations set forth in the Registration Rights
Agreement dated March 22, 2002 by and among the Company and the purchasers of
the Company's Series B Convertible Preferred Stock.

         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 March 19, 2002.


                                    VIROLOGIC, INC.


                                    By: /s/ William D. Young
                                       -----------------------------------------

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

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


                                       6.
<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.