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                                                                   EXHIBIT 10.4


                    INTELLECTUAL PROPERTY SECURITY AGREEMENT


        THIS INTELLECTUAL PROPERTY SECURITY AGREEMENT (this "AGREEMENT") is made
and entered into as November 14, 2002 by VIROLOGIC, INC., a Delaware corporation
(the "GRANTOR"), in favor of SDS Merchant Fund, L.P., as Collateral Agent, for
the benefit of the holders of the Notes (each a "SECURED PARTY" and collectively
the "SECURED PARTIES"). All capitalized terms used but not otherwise defined
herein shall have the respective meanings assigned thereto in the Exchange
Agreement (as defined below).

                              W I T N E S S E T H:

        WHEREAS, Grantor and the Secured Parties have entered into that certain
Exchange Agreement dated as of the date hereof (as from time to time amended,
supplemented or otherwise modified, the "EXCHANGE AGREEMENT");

        WHEREAS, pursuant to the Exchange Agreement, Grantor has issued to the
Secured Parties $12,045,987.94 in aggregate principal amount of Grantor's Series
C Convertible Secured Promissory Notes (as from time to time amended,
supplemented or otherwise modified, the "NOTES");

        WHEREAS, as collateral security for payment and performance of its
obligations under the Exchange Agreement, the Notes and the other Transaction
Documents, Grantor is willing to grant to the Collateral Agent (for the benefit
of the Secured Parties) a security interest in certain of its property and
assets; and

        WHEREAS, Grantor is contemporaneously entering into that certain
Security Agreement dated as of the date hereof in favor of the Collateral Agent
(for the benefit of the Secured Parties)(as from time to time amended,
supplemented or otherwise modified, the "SECURITY AGREEMENT"); and

        NOW, THEREFORE, in order to induce the Secured Parties to enter into the
Exchange Agreement and the other Transaction Documents and in consideration of
the premises and the mutual covenants contained herein, the parties hereto
hereby agree as follows:

        1. GRANT OF SECURITY. Grantor hereby grants to the Collateral Agent (for
the benefit of the Secured Parties), and hereby reaffirms its prior grant to the
Collateral Agent (for the benefit of the Secured Parties) pursuant to the
Security Agreement of, a first priority continuing security interest, subject to
Permitted Liens (as defined in the Security Agreement), in all of the following
(collectively, the "COLLATERAL"):

           (a) Patents. All of Grantor's right, title and interest, whether now
owned or hereafter acquired, in and to all United States issued patents and
patent applications (including without limitation the patents and patent
applications identified on Schedule I attached hereto and incorporated herein by
reference), including, without limitation, the inventions and improvements
described and claimed therein, and all reissues, divisions, continuations,


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continuations-in-part, substitutes, renewals, and extensions thereof, all
foreign patent applications based thereof and foreign patents issuing therefrom,
and all income, royalties, damages and payments now or hereafter due and/or
payable under or with respect to any of the foregoing, including, without
limitation, damages and payments for past, present and future infringements of
any of the foregoing and the right to sue for past, present and future
infringements of any of the foregoing, and all other rights of any kind
whatsoever of Grantor accruing thereunder or pertaining thereto (collectively,
the "PATENTS").

           (b) Trademarks. All of Grantor's right, title and interest, whether
now owned or hereafter acquired, in and to all United States trademarks, trade
names, trade dress, domain names, corporate names, company names, business
names, fictitious business names, trade styles, service marks, logos, other
business identifiers, prints and labels on which any of the foregoing have
appeared or appear, all registrations and recordings thereof, and all
applications (other than "intent to use" applications until a verified statement
of use is filed with respect to such applications) in connection therewith
(including without limitation each trademark, trade name, trade dress, domain
name, registration and application identified in Schedule II attached hereto and
incorporated herein by reference), and any renewals thereof, and all income,
royalties, damages and payments now or hereafter due and/or payable under or
with respect to any of the foregoing, including, without limitation, damages and
payments for past, present and future infringements of any of the foregoing and
the right to sue for past, present and future infringements of any of the
foregoing, and all rights corresponding thereto throughout the world (but only
such rights as now exist or may come to exist under applicable local law) and
all other rights of any kind whatsoever of Grantor accruing thereunder or
pertaining thereto (collectively, the "TRADEMARKS"), together in each case with
the goodwill of the business connected with the use of, and symbolized by, each
such Trademark.

           (c) Copyrights. All of Grantor's right, title and interest, whether
now owned or hereafter acquired, in and to all United States copyrights and
copyright applications (including without limitation the copyrights and
copyright applications identified on Schedule III attached hereto and
incorporated herein by reference) and all reissues, divisions, continuations,
continuations-in-part, substitutes, renewals, and extensions thereof, all
improvements thereon, and all income, royalties, damages and payments now or
hereafter due and/or payable under or with respect to any of the foregoing,
including, without limitation, damages and payments for past, present and future
infringements of any of the foregoing and the right to sue for past, present and
future infringements of any of the foregoing, and all other rights of any kind
whatsoever of Grantor accruing thereunder or pertaining thereto (collectively,
the "COPYRIGHTS").

           (d) Licenses. All license agreements regarding Patents, Trademarks or
Copyrights (other than "off the shelf" software) with any other party, whether
Grantor is a licensor or licensee under any such license agreement (including
without limitation the licenses listed on Schedule IV attached hereto and
incorporated herein by reference), as from time to time amended, supplemented or
otherwise modified, and all income, royalties, damages and payments now or
hereafter due and/or payable under or with respect to any of the foregoing, and
the right to prepare for sale, sell and advertise for sale, all inventory now or
hereafter owned by Grantor



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and now or hereafter covered by such licenses, and all other rights of any kind
whatsoever of Grantor accruing thereunder or pertaining thereto (collectively,
the "LICENSES").

           (e) Proceeds. To the extent not otherwise included, all proceeds of
any of the foregoing, including without limitation (i) any and all proceeds of
any guarantee, insurance or indemnity payable to Grantor from time to time with
respect to any of the Collateral; (ii) any and all payments (in any form
whatsoever) made or due and payable to Grantor from time to time as
consideration for any confiscation, condemnation, seizure or forfeiture of all
or any part of the Collateral by any governmental authority; (iii) all proceeds
of any sale, lease, license or other disposition of any of the Collateral or
rights therein whether or not the lien therein purportedly granted hereunder is
valid or attaches or is perfected; and (iv) any and all other amounts from time
to time paid or payable with respect to or in connection with any of the
Collateral.

        2. SECURED OBLIGATIONS. The security interests granted under this
Agreement (the "SECURITY INTERESTS") by Grantor secure the prompt and complete
payment and performance of all Secured Obligations (as such term is defined
herein). For purposes of this Agreement, "SECURED OBLIGATIONS" shall mean: (a)
all obligations and liabilities to the Secured Parties, whether now existing or
hereafter arising, under the Exchange Agreement, the Notes, this Agreement, the
Security Agreement, and/or any document or agreement related to any of the
foregoing and the due performance and compliance with the terms of the Exchange
Agreement, the Notes, this Agreement, the Security Agreement, and/or any
document or agreement related to any of the foregoing; (b) any and all sums
advanced by the Collateral Agent in order to preserve the Collateral or to
preserve the Secured Parties' security interest in the Collateral; and (c) in
the event of any proceeding for the collection or enforcement of any obligations
or liabilities of Grantor referred to in the immediately preceding clauses (a)
and (b) in accordance with the terms of the Exchange Agreement, the Notes, this
Agreement, the Security Agreement, and/or any document or agreement related to
the foregoing, the expenses of re-taking, holding, preparing for sale, selling
or otherwise disposing of or realizing on the Collateral, or of any other
exercise by the Collateral Agent (for the benefit of the Secured Parties) of its
rights hereunder, together with reasonable attorneys' fees and court costs. The
Security Interests granted by this Agreement are granted in conjunction with the
security interests granted to the Collateral Agent (for the benefit of the
Secured Parties) in certain assets of Grantor under the Security Agreement.

        3. FURTHER ASSURANCES.

           (a) Grantor agrees that from time to time, at the expense of Grantor,
Grantor will promptly execute and deliver all further instruments and documents
and take all further actions that may be necessary or desirable in the
Collateral Agent's reasonable determination, or that the Collateral Agent may
reasonably request, in order to (i) continue, perfect and protect any Security
Interest granted or purported to be granted hereby and (ii) enable the
Collateral Agent (for the benefit of the Secured Parties) to exercise and
enforce its rights and remedies hereunder with respect to any part of the
Collateral. Without limiting the generality of the foregoing, Grantor will
execute and file (with the appropriate governmental offices, authorities,
agencies and regulatory bodies in the United States) such supplements to this
Agreement and such financing or continuation statements, or amendments thereto,
and such other instruments or notices, including executed Notices, with the U.S.
Patent and Trademark Office and the U.S.



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Copyright Office, as may be necessary or desirable, or as the Collateral Agent
may reasonably request, in order to perfect and preserve the Security Interests
granted hereby.

           (b) If, before the Secured Obligations have been indefeasibly paid
and/or performed in full, Grantor shall (i) adopt, use, acquire or apply for
registration of any trademark, service mark or trade name (each deemed a "FUTURE
TRADEMARK"), (ii) apply for any U.S. and foreign patent or obtain any U.S. and
foreign patent or patent application (each deemed a "FUTURE PATENT"); (iii)
create or acquire any published or material unpublished works of authorship that
is registered with the U.S. Copyright Office (each deemed a "FUTURE COPYRIGHT");
or (iv) enter into any license agreement in respect of any Patent, Trademark or
Copyright that is not now identified on Schedule IV (each deemed a "FUTURE
LICENSE"); then the provisions of Section 1 above shall automatically apply
thereto, and Grantor shall give to Collateral Agent reasonably prompt notice
thereof in writing. Such written notice shall act to modify this Agreement
unilaterally by amending Schedule I, Schedule II, Schedule III or Schedule IV
hereto, as appropriate, to include any Future Trademark, Future Patent, Future
Copyright or Future License described therein.

           (c) Grantor agrees that simultaneously with the execution of this
Agreement, and thereafter upon any amendment of Schedule I, Schedule II or
Schedule III, Grantor shall execute notices in the form appended hereto as
Exhibit A, Exhibit B, or Exhibit C (each, a "NOTICE"), as appropriate, with
respect to all of the Collateral, now owned or hereafter acquired, and shall
deliver each Notice to Collateral Agent for the purpose of recordation at the
U.S. Patent and Trademark Office or the U.S. Copyright Office, as appropriate.

           (d) Grantor agrees that it (i) will not take any action, nor enter
into any license, royalty, assignment or other agreement which will conflict
with Grantor's obligations under this Agreement; (ii) will not take any action,
nor enter into any license, royalty, assignment or other agreement, except for
commercially reasonable purposes, which has the effect of diluting, reducing the
distinctiveness of or otherwise reducing the value of the Collateral, including
the unreasonable failure to maintain any patent or patent pending or
unreasonably allowing for the abandonment of any trademark or service mark
application or the cancellation or expiration of any trademark or service mark
registration; (iii) will give Collateral Agent thirty (30) days prior written
notice of any proposed license, royalty, assignment or other agreement relating
to the Collateral; and (iv) will actively defend any claim or allegation that
any of the Collateral infringes upon or misappropriates the proprietary rights
of any third party and will actively pursue any third-party infringers of the
Collateral unless otherwise agreed to by the Collateral Agent, which agreement
shall not be unreasonably withheld.

           (e) Grantor shall have the duty (i) with respect to the Trademarks,
to prosecute diligently any applications for any Trademarks pending as of the
date of this Agreement or thereafter filed, to maintain any trademark/service
mark registrations in effect as of the date of this Agreement or thereafter
obtained, and to preserve and maintain all rights in the Trademarks and any
registrations thereof and/or the applications therefor; (ii) with respect to the
Patents, to prosecute diligently any patent applications pending as of the date
of this Agreement or thereafter acquired or filed and to maintain any Patents
issued as of the date of this Agreement or thereafter issued and (iii) with
respect to the Copyrights, to register in the U.S. Copyright



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Office any works of authorship material to the business of Grantor; unless, in
each case, Grantor determines in its good faith business judgment that Grantor's
business would be better served by not taking such actions. Any expenses
incurred in connection with such applications, registrations and/or maintenance
activities shall be borne by Grantor.

           (f) Grantor shall not do any act or omit to do any act whereby any of
the Collateral may become dedicated or abandoned, except where such dedication
or abandonment (i) will not materially adversely affect the business, condition
(financial or otherwise), operations, performance, or properties of Grantor, and
(ii) is in the ordinary course of Grantor's business. Grantor agrees to notify
the Collateral Agent promptly and in writing if it learns that any of the
Collateral may become abandoned or dedicated or of any adverse determination or
any development (including without limitation the institution of any proceeding
in the U.S. Patent and Trademark Office, the U.S. Copyright Office, or any
court) regarding any material part of the Collateral.

           (g) Grantor shall have the duty to take any and all action which
reasonably may be necessary or desirable to protect the Collateral, including,
without limitation, the prosecution and defense of infringement actions
involving the Collateral unless otherwise agreed to by the Collateral Agent,
which agreement shall not be unreasonably withheld. During the continuance of an
Event of Default, the Collateral Agent shall have the right, but shall in no way
be obligated, to bring suit in its own or in Grantor's name to enforce and
protect rights to the Collateral in which event Grantor shall, at the request of
the Collateral Agent, do any and all lawful acts and execute any and all proper
documents reasonably required by the Collateral Agent in aid of such enforcement
and Grantor shall promptly, upon demand, reimburse and indemnify the Collateral
Agent for all reasonable costs and expenses incurred by the Collateral Agent in
the exercise of its rights under this subsection.

           (h) To preserve and protect the goodwill associated with the
Trademarks, Grantor covenants that it shall maintain the quality of the products
and services sold under or in connection with the Trademarks and shall not at
any time permit any impairment of the quality of such products and services, and
will provide the Collateral Agent with a certificate to such effect signed by an
officer of Grantor upon the reasonable request of the Collateral Agent.

           (i) Grantor shall continue to mark its products as required by
statute with the numbers of all appropriate Patents.

        4. FINANCING STATEMENTS. Grantor hereby irrevocably authorizes the
Collateral Agent at any time and from time to time to file in any Uniform
Commercial Code jurisdiction any initial financing statements and amendments or
continuations thereto that describe the Collateral. Grantor shall execute and
deliver as reasonably required by the Collateral Agent any additional financing
statements or other documents, together with any necessary amendments or
continuation statements so long as this Agreement remains in effect.

        5. RECEIPT OF PAYMENT. In the event an Event of Default (as hereinafter
defined) shall occur and be continuing and Grantor (or any of its affiliates,
subsidiaries, stockholders, directors, officers, employees or agents) shall
receive any proceeds of Collateral,



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including without limitation monies, checks, notes, drafts or any other items of
payment, Grantor shall hold all such items of payment in trust for the
Collateral Agent (for the benefit of the Secured Parties), and as the property
of the Collateral Agent (for the benefit of the Secured Parties), separate from
the funds of Grantor, and no later than the first business day following the
receipt thereof, Grantor shall cause the same to be forwarded to the Collateral
Agent (for the benefit of the Secured Parties) for its custody and possession as
additional Collateral.

        6. COVENANTS. Grantor covenants with the Collateral Agent (for the
benefit of the Secured Parties) that from and after the date of this Agreement
until termination hereof in accordance with Section 27 hereof:

        (a) TRANSFER OF COLLATERAL. Except for Permitted Liens or as otherwise
expressly permitted herein, other than the disposition of items of Collateral in
the ordinary course of Grantor's business as presently conducted, Grantor shall
not sell, assign, transfer, encumber or otherwise dispose of any Collateral
without the prior written consent of the Collateral Agent, which consent shall
not be unreasonably withheld. For purposes of this provision, "dispose of
Collateral" shall include, without limitation, the creation of a Lien (whether
voluntary or involuntary) on such Collateral.

        (b) FURTHER IDENTIFICATION OF COLLATERAL. Grantor will furnish to the
Collateral Agent from time to time, upon the request of the Collateral Agent,
statements and schedules further identifying and describing the Collateral and
such other reports in connection with the Collateral as the Collateral Agent may
reasonably request, all in reasonable detail.

        7. GENERAL WARRANTIES AND REPRESENTATIONS. Grantor represents and
warrants to the Collateral Agent (for the benefit of the Secured Parties) that:

        (c) Grantor is and, except as permitted by the Exchange Agreement, will
continue to be the owner of the Collateral hereunder, now owned and upon the
acquisition of the same, free and clear of all Liens other than the security
interest in favor of the Collateral Agent (for the benefit of the Secured
Parties) hereunder and under the Security Agreement and Permitted Liens, and
that it will defend such Collateral and any products and proceeds thereof
against all claims and demands of all third parties at any time claiming the
same or any interest therein adverse to the Collateral Agent.

        (d) Grantor has the full legal right and power and all authority and
approval required to enter into, execute and deliver this Agreement, to grant
the security interest of the Collateral Agent (for the benefit of the Secured
Parties) hereunder and to perform fully each of its obligations hereunder. This
Agreement has been duly executed and delivered and constitutes the valid and
binding obligation of Grantor enforceable in accordance with its terms, except
as may be limited by applicable bankruptcy, insolvency, reorganization,
moratorium, liquidation or similar laws relating to creditor's rights generally.
No approval or consent of any foreign, federal, state, country, local or other
governmental or regulatory body, and no approval or consent of any other Person
is required in connection with the execution and delivery by Grantor of this
Agreement, the grant of the security interest of the Collateral Agent (for the
benefit of the Secured Parties) hereunder and the consummation and performance
by Grantor of the



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transactions contemplated hereby. The execution and delivery of this Agreement,
the grant of the security interest of the Collateral Agent (for the benefit of
the Secured Parties) hereunder and the consummation and performance by Grantor
of the transactions contemplated hereby will not conflict with or result in the
breach or violation of any of the terms or conditions of, or constitute (or with
notice or lapse of time or both would constitute) a default under any material
instrument, contract or other agreement to which Grantor is a party or by or to
which it or its assets or properties are bound or subject or any statute or any
regulation, order, judgment or decree of any court or governmental or regulatory
body.

        (e) To the best of Grantor's knowledge, the Collateral does not infringe
any rights owned or possessed by any third party.

        (f) There are no claims, judgments or settlements to be paid by Grantor
or pending claims or litigation relating to the Collateral.

        (g) No action or proceeding is pending or, to Grantor's knowledge,
threatened seeking to limit, cancel or question the scope or validity of any of
the Collateral.

        (h) The actions contemplated under or in connection with the Transaction
Documents will not impair the legal right of Grantor to use any of the
Collateral.

        (i) Grantor has no knowledge of the existence of any right under any
patent, trademark, license agreement, trade name, trade secret, know-how,
confidential research, development and commercial information, or other
proprietary information held by any other person that would preclude Grantor
from publishing, distributing, marketing, selling, or using any product
currently made by it, being made for it or sold or used by it, imported by it or
exported by it, as the case may be, or to use any processes currently used by
it, or materially interfere with the ability of Grantor to carry on its business
as currently carried on, and Grantor has no knowledge of any claim to the
contrary that is reasonably likely to be made.

        (j) To the best of Grantor's knowledge, there are no other users of the
Trademarks or variations thereof that are similar enough to the Trademarks, with
due regard to goods and services with which the respective Trademarks are used,
as to be likely to cause confusion or mistake among consumers.

        (k) Grantor has complied with, and will continue for the duration of
this Agreement to comply with, the requirements set forth in 15 U.S.C. Sections
1051-1127, 17 U.S.C. Section 101, et seq., 35 U.S.C. Section 101 et seq. and any
other applicable statutes, rules and regulations in connection with its use of
the Collateral.

        (l) Set forth on Schedule IV is a list, which is complete and accurate
in all material respects as of the date hereof, of Licenses of Grantor necessary
for the conduct of its business as currently conducted or used in the selling or
marketing of Grantor's products, including the expiration date of such Licenses.
Each License of Grantor identified on Schedule IV is validly subsisting and has
not been adjudged invalid or unenforceable, in whole or in part, and is, to
Grantor's knowledge, valid and enforceable.



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        8. PATENT REPRESENTATIONS AND WARRANTIES. Grantor represents and
warrants as follows:

           (a) It is the sole, legal and beneficial owner of the entire right,
title and interest in and to each of the Patents, free and clear of any lien,
security interest, option, charge, pledge, registered user agreement, assignment
(whether conditional or not), or any other encumbrance except for the security
interests created hereunder and under the Security Agreement and Permitted
Liens. No effective financing statement or other instrument similar in effect
covering all or any part of such Collateral is on file in any recording office,
except such as may have been filed in favor of the Collateral Agent (for the
benefit of the Secured Parties).

           (b) Set forth on Schedule I is a list of all of the Patents owned by
Grantor necessary for the conduct of its business as currently conducted or used
in the selling or marketing of Grantor's products.

           (c) Each Patent of Grantor identified on Schedule I hereto is
subsisting and has not been adjudged unpatentable, invalid or unenforceable, in
whole or in part, and to the knowledge of Grantor is patentable, valid and
enforceable, and each Patent application of Grantor identified on Schedule I
hereto has been filed in conformity with applicable rules and procedures of the
U.S. Patent and Trademark Office.

        9. TRADEMARK REPRESENTATIONS AND WARRANTIES. Grantor represents and
warrants as follows:

            (a) It is the sole, legal and beneficial owner of the entire right,
title and interest in and to each of the Trademarks, free and clear of any lien,
security interest, option, charge, pledge, registered user agreement, assignment
(whether conditional or not), or covenant, or any other encumbrance, except for
the security interests created hereunder and under the Security Agreement and
Permitted Liens. No effective financing statement or other instrument similar in
effect covering all or any part of such Collateral is on file in any recording
office, including, without limitation, the U.S. Patent and Trademark Office,
except such as may have been filed in favor of the Collateral Agent (for the
benefit of the Secured Parties).

            (b) Set forth on Schedule II is a list of all of the Trademarks
owned by Grantor necessary for the conduct of its business as currently
conducted or used in the selling or marketing of Grantor's products.

            (c) Each Trademark of Grantor identified on Schedule II is validly
subsisting and has not been abandoned or adjudged invalid, unregistrable or
unenforceable, in whole or in part, and is, to Grantor's knowledge, valid,
registrable and enforceable.

            (d) Grantor has used consistent standards of quality in
manufacturing, distribution and marketing of each product sold and provision of
each service provided under any Trademark.

        10. COPYRIGHT REPRESENTATIONS AND WARRANTIES. Grantor represents and
warrants as follows:



                                      -8-
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            (a) It is the sole, legal and beneficial owner of the entire right,
title and interest in and to each of the Copyrights, free and clear of any lien,
security interest, option, charge, pledge, registered user agreement, assignment
(whether conditional or not), or covenant, or any other encumbrance, except for
the security interests created hereunder and under the Security Agreement and
Permitted Liens. No effective financing statement or other instrument similar in
effect covering all or any part of such Collateral is on file in any recording
office, including, without limitation, the U.S. Copyright Office, except such as
may have been filed in favor of the Collateral Agent (for the benefit of the
Secured Parties).

            (b) Set forth on Schedule III is a list of all of the Copyrights
owned by Grantor necessary for the conduct of its business as currently
conducted or materially used in the selling or marketing of Grantor's products.

            (c) Each Copyright of Grantor identified on Schedule III is validly
subsisting and has not been abandoned or adjudged invalid, unregistrable or
unenforceable, in whole or in part, and is, to Grantor's knowledge, valid and
enforceable.

        11. COLLATERAL AGENT APPOINTED ATTORNEY-IN-FACT. Without limiting any
other provision of this Agreement, upon the occurrence and during the
continuance of an Event of Default, Grantor hereby irrevocably appoints the
Collateral Agent (for the benefit of the Secured Parties), as Grantor's
attorney-in-fact, with full authority in the place and stead of Grantor and in
the name of Grantor or otherwise, from time to time in the Collateral Agent's
discretion, to take any action and to execute any instrument that the Collateral
Agent may reasonably deem necessary or advisable to accomplish the purposes of
this Agreement, including without limitation:

            (a) to ask, demand, collect, receive and give acquittances and
receipts for any and all moneys due and to become due under any License and, in
the name of Grantor or its own name or otherwise, to take possession of and
endorse and collect any checks, drafts, notes, acceptances or other instruments
for the payment of moneys due under any License and to file any claim or to take
any other action or proceeding in any court of law or equity or otherwise deemed
appropriate by the Collateral Agent for the purpose of collecting any and all
such moneys due under any License whenever payable;

            (b) to pay or discharge taxes, liens, security interests or other
encumbrances levied or placed on or threatened against the Collateral, to effect
any repairs or any insurance called for by the terms of this Agreement and to
pay all or any part of the premiums therefor and the costs thereof; and

            (c) to direct any party liable for any payment under any of the
Licenses to make payment of any and all moneys due and to become due thereunder
directly to the Collateral Agent or as the Collateral Agent shall direct;

            (d) to receive payment of and receipt for any and all moneys, claims
and other amounts due and to become due at any time in respect of or arising out
of any Collateral;


                                      -9-
<PAGE>

            (e) to commence and prosecute any suits, actions or proceedings at
law or in equity in any court of competent jurisdiction to collect the
Collateral or any part thereof and to enforce any other right in respect of any
Collateral;

            (f) to defend any suit, action or proceeding brought against Grantor
with respect to any Collateral;

            (g) to settle, compromise, or adjust any suit, action or proceeding
described above and, in connection therewith, to give such discharges or
releases as the Collateral Agent may deem appropriate; and

            (h) generally to sell, transfer, pledge, make any agreement with
respect to or otherwise deal with any of the Collateral as fully and completely
as though the Collateral Agent was the absolute owner thereof for all purposes,
and to do, at the Collateral Agent's option all acts and things which the
Collateral Agent deems necessary to protect, preserve or realize upon the
Collateral and the Collateral Agent's (for the benefit of the Secured Parties')
security interest therein, in order to effect the intent of this Agreement, all
as fully and effectively as Grantor might do.

This power of attorney is a power coupled with an interest and shall be
irrevocable. Notwithstanding the foregoing, Grantor further agrees to execute
any additional documents which the Collateral Agent may reasonably require in
order to confirm this power of attorney, or which the Collateral Agent may
reasonably deem necessary to enforce any of its rights contained in this
Agreement. The powers conferred on the Collateral Agent hereunder are solely to
protect its interests in the Collateral and shall not impose any duty upon it to
exercise any such powers. The Collateral Agent shall be accountable only for
amounts that it actually receives as a result of the exercise of such powers and
neither it nor any of its officers, directors, employees or agents shall be
responsible to Grantor for any act or failure to act, except for their own gross
(not mere) negligence or willful misconduct. The Grantor also authorizes the
Collateral Agent to execute, in connection with any sale provided for herein,
any endorsements, assignments or other instruments of conveyance or transfer
with respect to the Collateral.

        12. COLLATERAL AGENT MAY PERFORM. If Grantor fails to perform any
agreement contained herein after any applicable cure period, the Collateral
Agent may itself perform, or cause performance of, such agreement, and the
expenses of the Collateral Agent incurred in connection therewith shall be
payable by Grantor to the fullest extent permitted by applicable law.

        13. COLLATERAL AGENT'S DUTIES. The powers conferred on the Collateral
Agent hereunder are solely to protect the interest of the Collateral Agent (for
the benefit of the Secured Parties) in the Collateral and shall not impose any
duty upon it to exercise any such powers. Except for the safe custody of any
Collateral in its possession and the accounting for moneys actually received by
it hereunder the Collateral Agent shall have no duty as to any Collateral or as
to the taking of any necessary steps to preserve rights against other parties or
any other rights pertaining to any Collateral. The Collateral Agent shall be
deemed to have exercised reasonable care in the custody and preservation of the
Collateral in its possession if such



                                      -10-
<PAGE>

Collateral is accorded treatment substantially equal to that which such party
accords its own similar property.

        14. EVENTS OF DEFAULT. It is understood and agreed that the occurrence
of any one or more of the following shall constitute an "EVENT OF DEFAULT"
hereunder and shall entitle the Collateral Agent (for the benefit of the Secured
Parties) to take such actions as are elsewhere provided in this Agreement in
respect of Events of Default: (a) an "Event of Default" as defined in the Notes
shall have occurred and be continuing; or (b) any representation or warranty
made by Grantor herein shall prove to have been false in any material respect
when made; or (c) any covenant made by Grantor herein is breached, violated, or
not complied with and not cured within ten (10) days after notice thereof from
the Collateral Agent; or (d) any material uninsured damage to or loss, theft or
destruction of any of the Collateral shall occur; or (e) the security interests
granted herein do not constitute for any reason a first priority perfected
security interest in the Collateral covered thereby.

        15. RIGHTS AND REMEDIES UPON AN EVENT OF DEFAULT. If an Event of Default
shall have occurred and be continuing:

            (a) The Collateral Agent (for the benefit of the Secured Parties)
may exercise in respect of the Collateral, in addition to other rights and
remedies provided for herein or otherwise available to it, all the rights and
remedies of a secured party upon default under the Uniform Commercial Code as in
effect in the State of Delaware (the "Code") and also may (i) exercise any and
all rights and remedies of Grantor under, in connection with, or otherwise in
respect of, such Collateral, including the completion and filing of any Notice,
(ii) require Grantor to, and Grantor hereby agrees that it will at its expense
and upon request of the Collateral Agent forthwith, assemble all or part of the
documents embodying such Collateral as directed by the Collateral Agent and make
it available to the Collateral Agent, at a place to be designated by the
Collateral Agent that is reasonably convenient to both the Collateral Agent and
Grantor, (iii) subject to the rights of any lessor, occupy any premises owned or
leased by Grantor where documents embodying such Collateral or any part thereof
are assembled for a reasonable period in order to effectuate the rights and
remedies of the Collateral Agent (for the benefit of the Secured Parties)
hereunder or under applicable law, without obligation to Grantor in respect of
such occupation, (iv) license such Collateral or any part thereof, (v) with
notice as specified below, sell such Collateral or any part thereof in one or
more parcels at public or private sale, at any of the Collateral Agent's offices
or elsewhere, for cash, on credit or for future delivery, and upon such other
terms as the Collateral Agent may deem commercially reasonable, and (vi) without
prior notice to Grantor, direct any licensee of any Collateral to pay all
royalties and other payments which may be or which may thereafter become payable
to Grantor directly to the Collateral Agent or any designee of the Collateral
Agent, but the Collateral Agent shall give notice to Grantor of any such
direction no later than five (5) business days after giving any such direction.
Grantor agrees that at least ten (10) days' notice to Grantor of the time and
place of any public sale or the time after which any private sale is to be made
shall constitute reasonable notification. The Collateral Agent shall not be
obligated to make any sale of the Collateral regardless of notice of sale having
been given. The Collateral Agent may adjourn any public or private sale from
time to time by announcement at the time and place fixed therefor, and such



                                      -11-
<PAGE>

sale may, with further notice to Grantor, be made at the time and place to which
it was so adjourned.

            (b) All payments made under or in connection with or otherwise in
respect of the Collateral, and all cash proceeds received by the Collateral
Agent in respect of any sale of, collection from, or other realization upon all
or any part of such Collateral may, in the discretion of the Collateral Agent,
be held by the Collateral Agent, as collateral for, and then or at any time
thereafter applied against all or any part of the Secured Obligations. Any sale
or other disposition of the Collateral and the possession thereof by the
Collateral Agent shall be in compliance with all provisions of applicable law
(including applicable provisions of the Code).

        16. CONDUCT OF BUSINESS AFTER DEFAULT. The parties understand and agree
that the security interest granted to the Collateral Agent (for the benefit of
the Secured Parties) with respect to the Collateral, as defined in this
Agreement, together with the other Collateral, as defined in the Security
Agreement (the "OTHER COLLATERAL"), will and is intended to permit the
Collateral Agent and its successors and assigns, during the continuance of an
Event of Default as provided herein, to take title to and make use of all rights
to the Collateral in conjunction with the Other Collateral, all of which will
permit the Collateral Agent to manufacture and sell the products and/or provide
the services with which the Collateral is associated and maintain substantially
the same product specifications and quality and/or quality of services as
maintained by Grantor.

        17. PERFORMANCE BY COLLATERAL AGENT OF GRANTOR'S OBLIGATIONS. If Grantor
fails to perform or comply with any of its agreements contained herein after any
applicable cure period and the Collateral Agent, as provided for by the terms of
this Agreement, shall itself perform or comply, or otherwise cause performance
or compliance, with such agreements, the expenses of the Collateral Agent
incurred in connection with such performance or compliance shall be payable by
Grantor to the Collateral Agent on demand and shall constitute Secured
Obligations secured hereby.

        18. RIGHTS AND REMEDIES CUMULATIVE; NON-WAIVER; ETC. The enumeration of
the rights and remedies of the Collateral Agent (for the benefit of the Secured
Parties), set forth in this Agreement is not intended to be exhaustive and the
exercise by the Collateral Agent of any right or remedy shall not preclude the
exercise of any other rights or remedies, all of which shall be cumulative, and
shall be in addition to any other right or remedy given hereunder, or under any
other agreement between Grantor and the Collateral Agent and/or any Secured
Party or which may now or hereafter exist in law or in equity or by suit or
otherwise. No delay or failure to take action on the part of the Collateral
Agent in exercising any right, power or privilege shall operate as a waiver
thereof, nor shall any single or partial exercise of any such right, power or
privilege preclude other or further exercise thereof or the exercise of any
other right, power or privilege or shall be construed to be a waiver of any
Event of Default. No waiver by a party hereunder shall be effective unless it is
in writing and signed by the party making such waiver, and then only to the
extent specifically stated in such writing. No course of dealing between Grantor
and the Collateral Agent or the Collateral Agent's agents or employees shall be
effective to change, modify or discharge any provision of this Agreement or to
constitute a waiver of any Event of Default. Neither the Collateral Agent nor
any Secured Party shall have



                                      -12-
<PAGE>

any liability for any error, omission or delay of any kind occurring in the
handling or liquidation of the Collateral or for any damages resulting
therefrom, other than as a result of its gross negligence or willful misconduct.

        19. SUPPLEMENTAL DOCUMENTATION. At the Collateral Agent's request,
Grantor shall execute and deliver to the Collateral Agent, at any time or times
hereafter, all documents, instruments and other written matter that the
Collateral Agent may reasonably request to perfect and maintain perfected the
security interest of the Collateral Agent (for the benefit of the Secured
Parties) in the Collateral, in form and substance reasonably acceptable to the
Collateral Agent, and pay all charges, expenses and fees the Collateral Agent
may reasonably incur in filing any of such documents, and all taxes relating
thereto. Grantor agrees that a carbon, photographic, photostatic, or other
reproduction of this Agreement or a financing statement is sufficient as a
financing statement and may be filed by the Collateral Agent in any filing
office.

        20. WAIVERS. In addition to the other waivers contained herein, Grantor
hereby expressly waives, to the extent permitted by law: presentment for
payment, demand, protest, notice of demand, notice of protest, notice of default
or dishonor, notice of payments and nonpayments and all other notices and
consents to any action taken by the Collateral Agent (on behalf of the Secured
Parties) unless expressly required by this Agreement.

        21. NOTICE. Any notice shall be conclusively deemed to have been
received by any party hereto and be effective on the day on which delivered to
such party (against receipt therefor) at the address set forth below or such
other address as such party shall specify to the other parties in writing (or,
in the case of telephonic notice or notice by telecopy (where the receipt of
such message is verified by return) expressly provided for hereunder, when
received at such telephone or telecopy number as may from time to time be
specified in written notice to the other parties hereto or otherwise received),
or if sent prepaid by certified or registered mail return receipt requested on
the third business day after the day on which mailed, or if sent prepaid by a
national overnight courier service, on the first business day after the day on
which delivered to such service against receipt therefor, addressed to such
party at said address:

        (a) if to Grantor:

            ViroLogic, Inc.
            270 East Grand Avenue
            South San Francisco, California 94080
            Telephone:  (650) 635-1100
            Facsimile:
            Attn:  Chief Executive Officer



                                      -13-
<PAGE>

            with a copy simultaneously transmitted by like means to (which
              transmittal shall not constitute notice hereunder):

            Cooley Godward LLP
            4401 Eastgate Mall
            San Diego, California 92121
            Telephone:  (858) 550-6000
            Facsimile: (858) 453-3555

        (b) if to the Collateral Agent:

            SDS Merchant Fund, L.P.
            53 Forest Avenue
            Second Floor
            Old Greenwich, CT 06870
            Telephone:  (203) 967-5850 x75
            Facsimile: (203) 967-5851
            Attn: Steve Derby

            with a copy simultaneously transmitted by like means to (which
              transmittal shall not constitute notice hereunder):

            Drinker Biddle & Reath LLP
            One Logan Square
            18th and Cherry Streets
            Philadelphia, PA 19103
            Telephone:  (215) 988-2700
            Facsimile:  (215) 988-2757
            Attn:  Stephen T. Burdumy, Esq.

or to such other address as each party may designate for itself by like notice
given in accordance with this Section 21.

        22. DEFINITIONS. All terms defined in Article 9 of the Uniform
Commercial Code of the State of Delaware (the "CODE") and used in this Agreement
shall have the same definitions herein as specified in Article 9 of the Code,
and such definitions are hereby incorporated herein by reference and made a part
hereof.

        23. ENTIRE AGREEMENT. This Agreement and the other Transaction Documents
constitute and express the entire understanding between the parties hereto with
respect to the subject matter hereof and thereof, and supersede all prior
agreements and understandings, inducements, commitments or conditions, express
or implied, oral or written, except as herein contained. The express terms
hereof control and supersede any course of performance or usage of the trade
inconsistent with any of the terms hereof. Neither this Agreement nor any
portion or provision hereof may be changed, altered, modified, supplemented,
discharged, canceled,



                                      -14-
<PAGE>
terminated, or amended orally or in any manner other than by an agreement, in
writing signed by the parties hereto.

        24. SEVERABILITY. The provisions of this Agreement are independent of
and separable from each other. If any provision hereof shall for any reason be
held invalid or unenforceable, such invalidity or unenforceability shall not
affect the validity or enforceability of any other provision hereof, but this
Agreement shall be construed as if such invalid or unenforceable provision had
never been contained herein.

        25. SUCCESSORS AND ASSIGNS. This Agreement shall be binding upon the
successors and assigns of Grantor, and the rights, remedies, powers, and
privileges of the Collateral Agent (for the benefit of the Secured Parties)
hereunder shall inure to the benefit of the successors and assigns of the
Collateral Agent; provided, however, that Grantor shall not make any assignment
hereof without the prior written consent of the Collateral Agent.

        26. COUNTERPARTS; FACSIMILE SIGNATURES. This Agreement may be executed
in any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which when taken together shall constitute one and the same
agreement. A telephone line facsimile transmission of this Agreement bearing a
signature on behalf of a party hereto shall be legal and binding on such party.

        27. TERMINATION; RELEASE. Upon the indefeasible payment in full of all
Secured Obligations, this Agreement and all obligations of Grantor hereunder
shall terminate without delivery of any instrument or performance of any act by
any party, and the Collateral shall automatically be released from the Liens
created by this Agreement and all rights to such Collateral shall automatically
revert to Grantor. Notwithstanding the immediately preceding sentence, upon such
termination of this Agreement, the Collateral Agent, at the expense of Grantor,
shall reassign and redeliver such Collateral then held by or for the Secured
Parties and execute and deliver to Grantor such documents as Grantor shall
reasonably request to evidence such termination.

        28. PARAGRAPH HEADINGS. The paragraph headings used in this Agreement
are for convenience of reference only and are not to affect the construction
hereof or be taken into consideration in the interpretation hereof.

        29. INDEMNIFICATION. Grantor agrees to pay, and to save the Collateral
Agent and each Secured Party harmless from, any and all liabilities, costs and
expenses (including, without limitation, legal fees and expenses) (i) with
respect to, or resulting from, any delay in paying, any and all excise, sales or
other taxes which may be payable or determined to be payable with respect to any
of the Collateral, (ii) with respect to, or resulting from, any delay by Grantor
in complying with any law or regulation applicable to any of the Collateral,
(iii) in connection with any action taken by the Collateral Agent in exercising
its rights under this Agreement, except to the extent caused by Collateral
Agent's or such Secured Party's gross negligence or willful misconduct, and (iv)
in connection with the preparation and enforcement of



                                      -15-
<PAGE>

this Agreement and/or and document or agreement related thereto. The obligations
under this Section 29 shall survive termination of this Agreement.

        30. GOVERNING LAW.

            (a) This Agreement and the rights and obligations of Grantor
hereunder shall be governed by, and construed and interpreted in accordance
with, the law of the State of Delaware, except to the extent that under the Code
the laws of another jurisdiction govern matters of perfection and the effect of
perfection or non-perfection of any security interest granted hereunder.

            (b) Each party hereby expressly and irrevocably agrees and consents
that any suit, action or proceeding arising out of or relating to this Agreement
and the transactions contemplated herein may be instituted in any state or
federal court sitting in the State of Delaware, and, by the execution and
delivery of this Agreement, each party expressly waives any objection that it
may have now or hereafter to the laying of the venue or to the jurisdiction of
any such suit, action or proceeding, and irrevocably submits generally and
unconditionally to the jurisdiction of any such court in any such suit, action
or proceeding.

            (c) Each party agrees that service of process may be made by
personal service of a copy of the summons and complaint or other legal process
in any such suit, action or proceeding, or by registered or certified mail
(postage prepaid) to the address of such party provided by Section 21 hereof, or
by any other method of service provided for under the applicable laws in effect
in the State of Delaware.

            (d) Nothing contained in subsections (b) or (c) hereof shall
preclude any party from bringing any suit, action or proceeding arising out of
or relating to this Agreement in the courts of any place where any party or any
of such party's property or assets may be found or located. To the extent
permitted by the applicable laws of any such jurisdiction, each party hereby
irrevocably submits to the jurisdiction of any such court and expressly waives,
in respect of any such suit, action or proceeding, the jurisdiction of any other
court or courts which now or hereafter, by reason of its present or future
domicile, or otherwise, may be available to it.

            (e) IN ANY ACTION OR PROCEEDING TO ENFORCE OR DEFEND ANY RIGHTS OR
REMEDIES UNDER OR RELATED TO THIS AGREEMENT OR ANY AMENDMENT, INSTRUMENT,
DOCUMENT OR AGREEMENT DELIVERED OR THAT MAY IN THE FUTURE BE DELIVERED IN
CONNECTION WITH THE FOREGOING, EACH PARTY HEREBY AGREES, TO THE EXTENT PERMITTED
BY APPLICABLE LAW, THAT ANY SUCH ACTION OR PROCEEDING SHALL BE TRIED BEFORE A
COURT AND NOT BEFORE A JURY AND EACH PARTY HEREBY WAIVES, TO THE EXTENT
PERMITTED BY APPLICABLE LAW, ANY OBJECTION THAT IT MAY HAVE THAT EACH ACTION OR
PROCEEDING HAS BEEN BROUGHT IN AN INCONVENIENT FORUM.


                                      -16-
<PAGE>

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                                      -17-
<PAGE>

        IN WITNESS WHEREOF, Grantor has caused this Agreement to be duly
executed and delivered as of the date first above written.


                                            VIROLOGIC, INC.



                                            By: /s/ WILLIAM D. YOUNG
                                               -----------------------------
                                            Name: William D. Young
                                                 ---------------------------
                                            Title: Chairman & CEO
                                                  --------------------------


Acknowledged and agreed
to by the Collateral Agent:

SDS MERCHANT FUND, L.P.,
as Collateral Agent,
by its Managing Member,
SDS Capital Partners, L.L.C.


By: /s/ STEVE DERBY
   -----------------------------
Name: Steve Derby
     ---------------------------
Title: Managing Member
      --------------------------



                                      -18-