<PAGE>   1

                                                                     EXHIBIT 4.5

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED. NO SALE OR DISPOSITION MAY BE EFFECTED EXCEPT IN COMPLIANCE WITH RULE
144 UNDER SAID ACT OR WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED
THERETO OR AN OPINION OF COUNSEL FOR THE HOLDER, SATISFACTORY TO THE COMPANY,
THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE ACT OR RECEIPT OF A NO-ACTION
LETTER FROM THE SECURITIES AND EXCHANGE COMMISSION.

                                    --------

               WARRANT TO PURCHASE 22,100 SHARES OF COMMON STOCK

                                                                October 16, 1996

THIS CERTIFIES THAT, for value received, Lease Management Services, Inc.,
("Holder") is entitled to subscribe for and purchase twenty-two thousand one
hundred (22,100) shares of the fully paid and nonassessable Common Stock ("the
Shares") of ViroLogic, Inc., a Delaware corporation (the "Company"), at the
Warrant Price (as hereinafter defined), subject to the provisions and upon the
terms and conditions hereinafter set forth. As used herein, the term "Common
Stock" shall mean the Company's presently authorized Common Stock, and any
stock into which such Common Stock may hereafter be exchanged.

1. Warrant Price. The Warrant Price shall initially be one and 84/100 dollars
($1.84) per share, subject to adjustment as provided in Section 7 below.

2. Conditions to Exercise. The purchase right represented by this Warrant may
be exercised at any time, or from time to time, in whole or in part during the
term commencing on the date hereof and ending on the earlier of:

        (a) 5:00 P.M. California time on the sixth annual anniversary of this
        Warrant Agreement; or

        (b) the effective date of the merger of the Company with or into, the
        consolidation of the Company with, or the sale by the Company of all or
        substantially all of its assets to another corporation or other entity
        (other than such a transaction wherein the shareholders of the Company
        retain or obtain a majority of the voting capital stock of the
        surviving, resulting, or purchasing corporation); provided that the
        Company shall notify the registered Holder of this Warrant of the
        proposed effective date of the merger, consolidation, or sale at least
        30 days prior to the effectiveness thereof.

        In the event that, although the Company shall have given notice of a
        transaction pursuant to subparagraph (b) hereof, the transaction does
        not close on approximately the day specified by the Company, unless
        otherwise elected by the Holder any exercise of the Warrant subsequent
        to the giving of such notice shall be rescinded and the Warrant shall
        again be exercisable until terminated in accordance with this Paragraph
        2.

3. Method of Exercise; Payment; Issuance of Shares; Issuance of New Warrant.

(a) Cash Exercise. Subject to Section 2 hereof, the purchase right represented
by this Warrant may be exercised by the Holder hereof, in whole or in part, by
the surrender of this Warrant (with a duly executed Notice of Exercise in the
form attached hereto) at the principal office of the Company (as set forth in
Section 18 below) and by payment to the Company, by

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LMSI/VIROLOGIC Warrant
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check, of an amount equal to the then applicable Warrant Price per share
multiplied by the number of shares then being purchased. In the event of any
exercise of the rights represented by this Warrant, certificates for the shares
of stock so purchased shall be in the name of, and delivered to, the Holder
hereof, or as such Holder may direct (subject to the terms of transfer
contained herein and upon payment by such Holder hereof of any applicable
transfer taxes). Such delivery shall be made within 10 days after exercise of
the Warrant and at the Company's expense and, unless this Warrant has been
fully exercised or expired, a new Warrant having terms and conditions
substantially identical to this Warrant and representing the portion of the
Shares, if any, with respect to which this Warrant shall not have been
exercised, shall also be issued to the Holder hereof within 10 days after
exercise of the Warrant.

(b)  Net Issue Exercise. In the event that the Company's common stock is
publicly traded or the Company is to be subject to a merger, acquisition, or
other consolidation in which the Company is not the surviving entity, then in
lieu of exercising this Warrant pursuant to Section 3(a), Holder may elect to
receive shares equal to the value of this Warrant (or of any portion thereof
remaining unexercised) by surrender of this Warrant at the principal office of
the Company together with  notice of such election, in which event the Company
shall issue to Holder the number of shares of the Company's 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 Holder.

     Y = the number of shares of Common Stock purchasable under this Warrant (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 = Warrant exercise price (as adjusted to the date of such calculation).

(c)  Fair Market Value. For purposes of this Section 3, Fair Market Value of
one share of the Company's Common Stock shall mean:

     (i)   In the event of an Initial Public Offering, the per share Fair Market
     Value for the Common Stock shall be the Offering Price at which the
     underwriters sell Common Stock to the public; or

     (ii)  The average of the closing bid and asked prices of the Common Stock
     quoted in the Over-The-Counter Market Summary, the last reported sale price
     of the Common Stock or the closing price quoted on the Nasdaq National
     Market System ("NMS") or on any exchange on which the Common Stock is
     listed, whichever is applicable, as published in the Western Edition of The
     Wall Street Journal for the ten (10) trading days prior to the date of
     determination of fair market value; or

     (iii) If the Company shall be subject to a merger, acquisition or other
     consolidation in which the Company is not the surviving entity, pursuant to
     Section 2(b), the per share Fair Market Value for the Common Stock shall be
     the value received per share of Common Stock by all holders of the Common
     Stock as determined by the Board of Directors; or

                                       2
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LMSI/VIROLOGIC Warrant
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     (iv) If the Common Stock is not publicly traded, the per share fair market
     value of the Common Stock shall be as determined in good faith by the
     Company's Board of Directors unless Holder elects to have such fair market
     value determined by an appraiser, which election must be made by Holder
     within ten (10) business days of the date the Company notifies Holder of
     the fair market value as determined by its Board of Directors. In the event
     of such an appraisal, the cost thereof shall be borne by the Holder unless
     such appraisal results in a fair market value in excess of 115% of that
     determined by the Company's Board of Directors, in which event the Company
     shall bear the cost of such appraisal.

     In the event of 3(c)(iii), above, the Company's Board of Directors shall
     prepare a certificate, to be signed by an authorized Officer of the
     Company, setting forth in reasonable detail the basis for and method of
     determination of the per share Fair Market Value of the Common Stock. The
     Board will also certify to the Holder that this per share Fair Market Value
     will be applicable to all holders of the Company's Common Stock. Such
     certification must be made to Holder at least thirty (30) business days
     prior to the proposed effective date of the merger, consolidation, sale, or
     other triggering event as defined in 3(c)(iii).

(d) Automatic Exercise. To the extent this Warrant is not previously exercised,
it shall be automatically exercised in accordance with Sections 3(b) and 3(c)
hereof (even if not surrendered) immediately before: (i) its expiration or (ii)
the consummation of any consolidation or merger of the Company, or any sale or
transfer of a majority of a company's assets pursuant to Section 2(b).

4. Representations and Warranties of Holder and Restrictions on Transfer
Imposed by the Securities Act of 1933.

(a) Representations and Warranties by Holder. The Holder represents and
warrants to the Company with respect to this purchase as follows:

     (i) The Holder has substantial experience in evaluating and investing in
     private placement transactions of securities of companies similar to the
     Company so that the Holder is capable of evaluating the merits and risks of
     its investment in the Company and has the capacity to protect its
     interests.

     (ii) The Holder is acquiring the Warrant and the Shares of Common Stock
     issuable upon exercise of the Warrant (collectively the "Securities") for
     investment for its own account and not with a view to, or for resale in
     connection with, any distribution thereof. The Holder understands that the
     Securities have not been registered under the Act by reason of a specific
     exemption from the registration provisions of the Act which depends upon,
     among other things, the bona fide nature of the investment intent as
     expressed herein. In this connection, the Holder understands that, in the
     view of the Securities and Exchange Commission (the "SEC"), the statutory
     basis for such exemption may be unavailable if this representation was
     predicted solely upon a present intention to hold the Securities for the
     minimum capital gains period specified under tax statutes, for a deferred
     sale, for or until an increase or decrease in the market price of the
     Securities or for a period of one year or any other fixed period in the
     future.

     (iii) The Holder acknowledges that the Securities must be held indefinitely
     unless subsequently registered under the Act or an exemption from such
     registration is available. The Holder is aware of the provisions of Rule
     144 promulgated under the Act ("Rule 144") which permits limited resale of
     securities purchased in a private



                                       3
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LMSI/VIROLOGIC Warrant
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     placement subject to the satisfaction of certain conditions, including, in
     case the securities have been held for less than three years, the
     existence of a public market for the shares, the availability of certain
     public information about the Company, the resale occurring not less than
     two years after a party has purchased and paid for the security to be
     sold, the sale being through a "broker's transaction" or in a transaction
     directly with a "market maker" (as provided by Rule 144(f)) and the number
     of shares or other securities being sold during any three-month period not
     exceeding specified limitations.

     (iv) The Holder further understands that at the time the Holder wishes to
     sell the Securities there may be no public market upon which such a sale
     may be effected, and that even if such a public market exists, the Company
     may not be satisfying the current public information requirements of Rule
     144, and that in such event, the Holder may be precluded from selling the
     Securities under Rule 144 unless a) a three-year minimum holding period
     has been satisfied and b) the Holder was not at the time of the sale nor
     at any time during the three-month period prior to such sale an affiliate
     of the Company.

     (v) The Holder has had an opportunity to discuss the Company's business,
     management and financial affairs with its management and an opportunity to
     review the Company's facilities. The Holder understands that such
     discussions, as well as the written information issued by the Company,
     were intended to describe the aspects of the Company's business and
     prospects which it believes to be material but were not necessarily a
     thorough or exhaustive description.

(b) Legends. Each certificate representing the Securities shall be endorsed
with the following legend:

          THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
          1933 AND MAY NOT BE TRANSFERRED UNLESS COVERED BY AN EFFECTIVE
          REGISTRATION STATEMENT UNDER SAID ACT, A "NO ACTION" LETTER FROM THE
          SECURITIES AND EXCHANGE COMMISSION WITH RESPECT TO SUCH TRANSFER, A
          TRANSFER MEETING THE REQUIREMENTS OF RULE 144 OF THE SECURITIES AND
          EXCHANGE COMMISSION, OR (IF REASONABLY REQUIRED BY THE COMPANY) AN
          OPINION OF COUNSEL SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY
          SUCH TRANSFER IS EXEMPT FROM SUCH REGISTRATION.

The Company need not register a transfer of Securities unless the conditions
specified in the foregoing legend are satisfied. The Company may also instruct
its transfer agent not to register the transfer of any of the Shares unless the
conditions specified in the foregoing legend are satisfied.

(c) Removal of Legend and Transfer Restrictions. The legend relating to the Act
endorsed on a certificate pursuant to paragraph 4(b) of this Warrant and the
stop transfer instructions with respect to the Securities represented by such
certificate shall be removed and the Company shall issues a certificate without
such legend to the Holder of the Securities if (i) the Securities are
registered under the Act and a prospectus meeting the requirements of Section
10 of the Act is available or (ii) the Holder provides to the Company an
opinion of counsel for the Holder reasonably satisfactory to the Company, or a
no-action letter or interpretive opinion of the staff of the SEC reasonably
satisfactory to the Company, to the effect that public sale, transfer or
assignment of the Securities may be without registration and without compliance
with any restrictions such as Rule 144.


                                       4
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LMSI/VIROLOGIC Warrant
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5. Condition of Transfer or Exercise of Warrant. It shall be a condition to any
transfer or exercise of this Warrant that at the time of such transfer or
exercise, the Holder shall provide the Company with a representation in writing
that the Holder of transferee is acquiring this Warrant and the shares of Common
Stock to be issued upon exercise, for investment purposes only and not with a
view to any sale or distribution, or a statement of pertinent facts covering any
proposed distribution. As a further condition to any transfer of this Warrant or
any or all of the shares of Common Stock issuable upon exercise of this Warrant,
other than a transfer registered under the Act, the Company must have received a
legal opinion, in form and substance satisfactory to the Company and its
counsel, reciting the pertinent circumstances surrounding the proposed transfer
and stating that such transfer is exempt from the registration and prospectus
delivery requirements of the Act. Each certificate evidencing the shares issued
upon exercise of the Warrant or upon any transfer of the shares (other than a
transfer registered under the Act or any subsequent transfer of shares so
registered) shall, at the Company's option, contain a legend in form and
substance satisfactory to the Company and its counsel, restricting the transfer
of the shares to sales or other dispositions exempt from the requirements of the
Act.

     As further condition to each transfer, the transferee shall receive and
accept a Warrant, of like tenor and date, executed by the Company.

6.   Stock Fully paid; Reservation of Shares. All Shares which may be issued
upon the exercise of the rights represented by this Warrant will, upon issuance,
be fully paid and nonassessable, and free from all taxes, liens, and charges
with respect to the issue thereof. During the period within which the rights
represented by this Warrant may be exercised, the Company will at all times have
authorized, and reserved for issuance upon exercise of the purchase rights
evidenced by this Warrant, a sufficient number of shares of its Common Stock to
provide for the exercise of the rights represented by this Warrant.

7.   Adjustments, Etc.

     7.1 Adjustment for Stock Splits and Combinations. If the Company, at any
     time or from time to time, effects a subdivision of, or combines, the
     outstanding shares of Common Stock, by stock split or stock dividend or by
     reverse stock split, respectively, then, and in each such event, the
     Warrant Price in effect immediately prior thereto shall immediately be
     proportionately decreased or increased, as the case may be, and the number
     of shares of Common Stock issuable at that time upon exercise of this
     warrant shall be proportionately increased or decreased, as the case may
     be.

     7.2 Adjustment for Recapitalization, Reclassification, or Exchange. If, at
     any time or from time to time, the Common Stock issuable upon exercise of
     this Warrant is changed into the same or a different number of shares of
     any other class or classes of stock of the Company, whether by
     recapitalization, reclassification or other exchange (other than as
     provided for elsewhere in this Section 7), then, and in each such event,
     the Holder shall have the right thereafter to purchase the kind and amount
     of stock and other securities and property receivable upon such
     recapitalization, reclassification or other exchange, by holders of the
     number of shares of Common Stock with respect to which this Warrant might
     have been exercised immediately prior to such recapitalization,
     reclassification or other exchange, all subject to further adjustment as
     provided herein.

     7.3 Reorganization, Mergers, Consolidations or Transfers of Assets. If, at
     any time or from time to time, there is a capital reorganization of the
     Common Stock (other than as provided for elsewhere in this Section 7) or a
     merger or consolidation of the Company

                                       5
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LMSI/VIROLOGIC Warrant
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      with or into another corporation, or a transfer of all or substantially
      all of the Company's assets to any other person, then, and in, and as a
      part of, each such event, provision shall be made so that the Holder
      shall thereafter be entitled to receive upon exercise of this Warrant the
      number of shares of stock or other securities or property of the Company,
      or, if applicable, of the resulting successor corporation, to which a
      holder of the number of shares of Common Stock issuable upon exercise of
      this Warrant would have been entitled on such capital reorganization,
      merger, consolidation or transfer, all subject to further adjustment as
      provided herein.

      7.4 Notices of Record Date. In the event of (a) 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
      or other distribution, or (b) any capital reorganization of the Company,
      any reclassification, recapitalization or exchange of the capital stock
      of the Company, or any merger or consolidation of the Company with or
      into another corporation, or any transfer of all or substantially all of
      the assets of the Company to any other person, or any voluntary or
      involuntary dissolution, liquidation or winding up of the Company, the
      Company shall mail to the Holder, at least 10 days prior to the record
      date specified therein, a notice specifying (x) the date on which any
      such record is to be taken for the purpose of such dividend or
      distribution, (y) the date on which any such reorganization,
      recapitalization, reclassification, exchange, consolidation, merger,
      transfer, dissolution, liquidation or winding up is expected to become
      effective, and (z) the time, if any, that is to be fixed, as to when the
      holders of record of Common Stock (or other securities) shall be entitled
      to exchange their shares of Common Stock (or other securities) for
      securities or other property deliverable upon such reorganization,
      recapitalization, reclassification, exchange, consolidation, merger,
      transfer, dissolution, liquidation or winding up.

      7.5 Reservation of Stock Issuable Upon Exercise. The Company at all times
      reserve and keep available out of its authorized but unissued shares of
      Common Stock such number of its shares of Common Stock as shall from time
      to time be sufficient to effect the exercise of this Warrant and all
      other rights or options to purchase Common Stock, and to permit the
      conversion of all stock or other securities convertible into Common
      Stock, as may be outstanding from time to time. If at any time the number
      of authorized but unissued shares of Common Stock shall not be sufficient
      for such purposes, 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.

8. Notice of Adjustments. Whenever any Warrant Price shall be adjusted pursuant
to Section 7 hereof, the Company shall prepare a certificate signed by its chief
financial officer setting forth, in reasonable detail, the event requiring the
adjustment, the amount of the adjustment, the method by which such adjustment
was calculated, and the Warrant Price and number of shares issuable upon
exercise of the Warrant after giving effect to such adjustment, and shall cause
copies of such certificate to be mailed (by certified or registered mail,
return receipt required, postage prepaid) within thirty (30) days of such
adjustment to the Holder of this warrant as set forth in Section 18 hereof.

9. "Market Stand-Off" Agreement. Holder hereby agrees that for a period of up
to 180 days following the effective date of the first registration statement of
the Company covering common stock (or other securities) to be sold on its
behalf in an underwritten public offering, it will not, to the extent requested
by the Company and any underwriter, sell or otherwise transfer or dispose of
(other than to donees or transferees who agree to be similarly bound) any of
the Shares at any time during such period except common stock included in such
registration; provided, however, that all officers and directors of the Company
who hold


                                       6
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LMSI/VIROLOGIC Warrant
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securities of the Company or options to acquire securities of the Company
and all other persons with registration rights enter into similar agreements.

10.  Transferability of Warrant. This Warrant is transferable on the books of
the Company at its principal office by the registered Holder hereof upon
surrender of this Warrant properly endorsed, subject to compliance with
applicable federal and state securities laws. The Company shall issue and
deliver to the transferee a new Warrant representing the Warrant so
transferred. Upon any partial transfer, the Company will issue and deliver to
Holder a new Warrant with respect to the Warrant not so transferred. Holder
shall not have any right to transfer any portion of this Warrant to any direct
competitor of the Company.

11.  No Fractional Shares. No fractional share of Common Stock will be issued
in connection with any exercise hereunder, but in lieu of such fractional share
the Company shall make a cash payment therefor upon the basis of the Warrant
Price then in effect.

12.  Charges, Taxes and Expenses. Issuance of certificates for shares of Common
Stock upon the exercise of this Warrant shall be made without charge to the
Holder for any United States or state of the United States documentary stamp
tax or other incidental expense in respect of the issuance of such certificate,
all of which taxes and expenses shall be paid by the Company, and such
certificates shall be issued in the name of the Holder.

13.  No Shareholder Rights Until Exercise. This Warrant does not entitle the
Holder hereof to any voting rights or other rights as a shareholder of the
Company prior to the exercise hereof.

14.  Registry of Warrant. The Company shall maintain a registry showing the
name and address of the registered Holder of this Warrant. This Warrant may be
surrendered for exchange or exercise, in accordance with its terms, at such
office or agency of the Company, and the Company and Holder shall be entitled
to rely in all respects, prior to written notice to the contrary, upon such
registry.

15.  Loss, Theft, Destruction or Mutilation of Warrant. Upon receipt by the
Company of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Warrant, and, in the case of loss, theft, or
destruction, or indemnity reasonably satisfactory to it, and, if mutilated,
upon surrender and cancellation of this Warrant, the Company will execute and
deliver a new Warrant, having terms and conditions substantially identical to
this Warrant, in lieu hereof.

16.  Miscellaneous.

     (a)  Issue Date. The provisions of this Warrant shall be construed and
     shall be given effect in all respect as if it had been issued and
     delivered by the Company on the date hereof.

     (b)  Successors. This Warrant shall be binding upon any successors or
     assigns of the Company.

     (c)  Governing Law. This Warrant shall be governed by and construed in
     accordance with the laws of the State of California.

     (d)  Headings. The Headings used in this Warrant are used for convenience
     only and are not to be considered in construing or interpreting this
     Warrant.

     (e)  Saturdays, Sundays, Holidays. If the last or appointed day for the
     taking of any action or the expiration of any right required or granted
     herein shall be a Saturday or a

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LMSI/VIROLOGIC Warrant
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          Sunday or shall be a legal holiday in the State of California, then
such action may be taken or such right may be exercised on the next succeeding
day not a legal holiday.

17. No Impairment. The Company will not, by amendment of its Articles of
Incorporation or any other voluntary action, avoid or see to avoid the
observance or performance of any of the terms of this Warrant, but will at all
times in good faith assist in the carrying out of all such terms and in the
taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder hereof against impairment.

18. Addresses. Any notice required or permitted hereunder shall be in writing
and shall be mailed by overnight courier, registered or certified mail, return
receipt required, and postage pre-paid, or otherwise delivered by hand or by
messenger, addressed as set forth below, or at such other address as the
Company or the Holder hereof shall have furnished to the other party.

               If to the Company:  ViroLogic, Inc.
                                   270 East Grand Avenue
                                   South San Francisco, CA 94080
                                   Attn:

               If to the Holder:   Lease Management Services, Inc.
                                   2500 Sand Hill Road, Ste. 101
                                   Menlo Park, CA 94025
                                   Attn: Barbara B Kaiser, EVP/GM

IN WITNESS WHEREOF, ______________ has caused this Warrant to be executed by
its officers thereunto duly authorized.

Dated as of October 16, 1996

                                   VIROLOGIC, INC.

                                   BY: MARTIN H. GOLDSTEIN
                                       ---------------------
                                       Martin H. Goldstein

                                   TITLE: President & CFO
                                          ------------------

                                       8

<PAGE>   9
                               NOTICE OF EXERCISE



TO:



1.   The undersigned Warrantholder ("Holder") elects to acquire shares of the
     Common Stock of __________________ )(the "Company), pursuant to the terms
     of the Stock Purchase Warrant dated _____________ , 199_ (the "Warrant").

2.   The Holder exercises its rights under the Warrant as set forth below:

          (    )    The Holder elects to purchase______ shares of Common Stock
                    as provided in Section 3(a), (c) and tenders herewith a
                    check in the amount of $____ as payment of the purchase
                    price.

          (    )    The Holder elects to convert the purchase rights into shares
                    of Common Stock as provided in Section 43(b), (c) of the
                    Warrant.

3.   The Holder surrenders the Warrant with this Notice of Exercise.

4.   The Holder represents that it is acquiring the aforesaid shares of Common
     Stock for investment and not with a view to, or for resale in connection
     with, distribution and that the Holder has no present intention of
     distributing or reselling the shares.

5.   Please issue a certificate representing the shares of Common Stock in the
     name of the Holder or in such other name as is specified below:

          Name:
          Address:


          Taxpayer I.D.:



                                             -------------------------------
                                             (Holder)

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

                                             Title:
                                                   -------------------------
                                             Date:
                                                   -------------------------