<PAGE>
                                                                    EXHIBIT 10.6



                                                                       EXHIBIT C
                                                                   TO SECURITIES
                                                                        PURCHASE
                                                                       AGREEMENT


                          REGISTRATION RIGHTS AGREEMENT

        REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of November
14, 2002, by and among ViroLogic, Inc., a corporation organized under the laws
of the State of Delaware (the "COMPANY"), and the undersigned (together with
their respective affiliates, the "INITIAL INVESTORS").

                                    WHEREAS:

        A. In connection with the Securities Purchase Agreement, dated as of
November 14, 2002, by and among the Company and certain of the Initial Investors
(the "SECURITIES PURCHASE AGREEMENT"), the Company has agreed, upon the terms
and subject to the conditions contained therein, to issue and sell to those
Initial Investors (i) shares of its Series C Convertible Preferred Stock (the
"PREFERRED STOCK") that are convertible into shares of the Company's common
stock, par value $.001 per share (the "COMMON STOCK"), upon the terms and
subject to the limitations and conditions set forth in the Certificate of
Designations, Rights and Preferences with respect to such Preferred Stock (the
"CERTIFICATE OF Designation") and (ii) warrants (the "SERIES C WARRANTS") to
acquire shares of Common Stock. The shares of Common Stock issuable upon
conversion of the Preferred Stock are referred to herein as the "CONVERSION
SHARES."

        B. In connection with the Exchange Agreement, dated as of November 14,
2002, by and among the Company and certain of the Initial Investors (the
"EXCHANGE AGREEMENT"), the Company has agreed, upon the terms and subject to the
conditions contained therein, to issue to those Initial Investors (i) promissory
notes (the "NOTES") that, under certain circumstances, will be automatically
converted into shares of Preferred Stock, and (ii) in the event that the Notes
are so converted, warrants (the "ADDITIONAL WARRANTS" and, together with the
Series C Warrants, the "WARRANTS") to acquire shares of Common Stock in exchange
for certain warrants currently held by such Initial Investors. The shares of
Common Stock issuable upon exercise of or otherwise pursuant to the Warrants are
referred to herein as the "WARRANT SHARES."

        C. To induce the Initial Investors to execute and deliver the Securities
Purchase Agreement and the Exchange Agreement, as applicable, the Company has
agreed to provide certain registration rights under the Securities Act of 1933,
as amended, and the rules and regulations thereunder, or any similar successor
statute (collectively, the "SECURITIES Act"), and applicable state securities
laws.

        NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Company and the
Initial Investors hereby agree as follows:

<PAGE>

        1. DEFINITIONS.

               (a) As used in this Agreement, the following terms shall have the
following meanings:

                      (i) "INVESTORS" means the Initial Investors and any
transferees or assignees who agree to become bound by the provisions of this
Agreement in accordance with Section 10 hereof.

                      (ii) "REGISTER," "REGISTERED," and "REGISTRATION" refer to
a registration effected by preparing and filing a Registration Statement or
Statements in compliance with the Securities Act and pursuant to Rule 415 under
the Securities Act or any successor rule providing for offering securities on a
continuous basis ("RULE 415"), and the declaration or ordering of effectiveness
of such Registration Statement by the United States Securities and Exchange
Commission (the "SEC").

                      (iii) "REGISTRABLE SECURITIES" means (a) the Conversion
Shares, (b) the Warrant Shares and (c) any shares of capital stock issued or
issuable, from time to time (with any adjustments), as a distribution or
dividend on or in exchange for or otherwise with respect to any of the
foregoing, whether as default payments or otherwise.

                      (iv) "REGISTRATION STATEMENT" means a registration
statement of the Company under the Securities Act.

               (b) Capitalized terms used herein and not otherwise defined
herein shall have the respective meanings set forth in the Securities Purchase
Agreement.

        2. REGISTRATION.

               (a) Mandatory Registration.

                      (i) The Company shall use its best efforts to prepare
promptly and file with the SEC as soon as practicable, but in no event later
than the forty-fifth (45th) day following the Closing Date (the "FIRST FILING
DATE"), a Registration Statement on Form S-3 (or, if Form S-3 is not then
available, on such form of Registration Statement as is then available to effect
a registration of all of the Registrable Securities to be so registered, subject
to the consent of the Initial Investors whose Registrable Securities are being
so registered) covering the resale of all of the Conversion Shares underlying
the shares of Preferred Stock and the Warrant Shares underlying the Series C
Warrants issued to the Initial Investors pursuant to the Securities Purchase
Agreement (and any other Registrable Securities related to such Conversion
Shares). The Registration Statement filed hereunder, to the extent allowable
under the Securities Act and the Rules promulgated thereunder (including Rule
416), shall state that such Registration Statement also covers such
indeterminate number of additional shares of Common Stock as may become issuable
upon conversion of such Preferred Stock or exercise of such Series C Warrants to
prevent dilution resulting from stock splits, stock dividends or similar
transactions. The Registrable Securities included in the Registration Statement
shall be allocated to the Investors as set forth in Section 12(k) hereof. The
Registration Statement (and each amendment or supplement thereto, and each
request for acceleration of


                                       2
<PAGE>

effectiveness thereof) shall be provided to (and subject to the approval of,
which shall not be unreasonably withheld) the Initial Investors and their
counsel prior to its filing or other submission.

                      (ii) In the event that the Company obtains the Authorized
Stock Approval and the NASD Rule Approval (as such terms are defined in the
Securities Purchase Agreement and the Exchange Agreement), the Company shall use
its best efforts to prepare promptly and file with the SEC as soon as
practicable, but in no event later than the forty-fifth (45th) day following the
date (the "STOCKHOLDER APPROVAL DATE") on which the Company obtains such
Authorized Stock Approval (the "SECOND FILING DATE" and, together with the First
Filing Date, the "FILING DATES"), a Registration Statement on Form S-3 (or, if
Form S-3 is not then available, on such form of Registration Statement as is
then available to effect a registration of all of the Registrable Securities to
be so registered, subject to the consent of the Initial Investors whose
Registrable Securities are being so registered) covering the resale of all of
the Conversion Shares underlying the shares of Preferred Stock issued to the
Initial Investors pursuant to the Exchange Agreement and all of the Warrant
Shares underlying the Additional Warrants issued to the Initial Investors
pursuant to the Exchange Agreement (and any other Registrable Securities related
to such Conversion Shares or Warrant Shares). The Registration Statement filed
hereunder, to the extent allowable under the Securities Act and the Rules
promulgated thereunder (including Rule 416), shall state that such Registration
Statement also covers such indeterminate number of additional shares of Common
Stock as may become issuable upon conversion of such Preferred Stock and
exercise of such Additional Warrants to prevent dilution resulting from stock
splits, stock dividends or similar transactions. The Registrable Securities
included in the Registration Statement shall be allocated to the Investors as
set forth in Section 12(k) hereof. The Registration Statement (and each
amendment or supplement thereto, and each request for acceleration of
effectiveness thereof) shall be provided to (and subject to the approval of,
which shall not be unreasonably withheld) the Initial Investors and their
counsel prior to its filing or other submission.

               (b) Payments by the Company. The Company shall use its best
efforts to cause the Registration Statements required to be filed pursuant to
Section 2(a) hereof to become effective as soon as practicable, but in no event
later than the one hundredth (100th) day following (1) the Closing Date (in the
case of the Registration Statement required to be filed pursuant to Section
2(a)(i) hereof) or (2) the Stockholder Approval Date (in the case of the
Registration Statement required to be filed pursuant to Section 2(a)(ii)
hereof). At the time of effectiveness, the Company shall ensure that such
Registration Statement covers all of the Registrable Securities issuable at such
time pursuant to the Preferred Stock and/or the Warrants required to be included
thereon (including, if necessary, by filing an amendment prior to the effective
date of the Registration Statement to increase the number of shares covered
thereby). If (i) (A) the Registration Statement required to be filed by the
Company pursuant to Section 2(a)(i) hereof is not filed with the SEC prior to
the First Filing Date or declared effective by the SEC on or before the one
hundred thirtieth (130th) day after the Closing Date (the "FIRST REGISTRATION
DEADLINE"), or (B) the Company has obtained the Authorized Stock Approval and
the Registration Statement required to be filed by the Company pursuant to
Section 2(a)(ii) hereof is not filed with the SEC prior to the Second Filing
Date or declared effective by the SEC on or before the one hundred thirtieth
(130th) day after the Stockholder Approval Date (the "SECOND REGISTRATION
DEADLINE" and, together with the First Registration Deadline, the "REGISTRATION
DEADLINES"), or (C) any Registration Statement required to



                                       3
<PAGE>

be filed by the Company pursuant to Section 4(b) hereof is not declared
effective by the SEC within sixty (60) days after the applicable Registration
Trigger Date (as defined in Section 4(b) hereof), or (ii) if, after any such
Registration Statement has been declared effective by the SEC, sales of any of
the Registrable Securities required to be covered by such Registration Statement
(including any Registrable Securities required to be registered pursuant to
Section 4(b) hereof) cannot be made pursuant to such Registration Statement (by
reason of a stop order or the Company's failure to update the Registration
Statement or any other reason outside the control of the Investors), except as
otherwise provided herein or (iii) the Common Stock is not listed or included
for quotation on the Nasdaq National Market ("NNM"), the Nasdaq SmallCap Market
("SMALLCAP"), the New York Stock Exchange (the "NYSE") or the American Stock
Exchange (the "AMEX") at any time after the applicable Registration Deadline
hereunder, then the Company will make payments to the Investors in such amounts
and at such times as shall be determined pursuant to this Section 2(b) as
partial relief for the damages to the Investors by reason of any such delay in
or reduction of their ability to sell the Registrable Securities (which remedy
shall not be exclusive of any other remedies available at law or in equity). The
Company shall pay to each Investor an amount equal to the product of (i) the
aggregate purchase price of the Preferred Stock and/or Warrants acquired
pursuant to the Securities Purchase Agreement or the Exchange Agreement or upon
conversion of the Notes acquired pursuant to the Exchange Agreement, as
applicable, and held by such Investor (including, without limitation, Preferred
Stock that has been converted into Conversion Shares and Warrants that have been
exercised for Warrant Shares then held by such Investor) (the "AGGREGATE SHARE
PRICE"), multiplied by (ii) two hundredths (.02), for each thirty (30) day
period (or portion thereof) (A) after the applicable Filing Date and prior to
the date the Registration Statement is filed with the SEC pursuant to Section
2(a), (B) after the applicable Registration Deadline and prior to the date the
Registration Statement filed pursuant to Section 2(a) is declared effective by
the SEC, (C) after the sixtieth (60th) day following a Registration Trigger Date
(as defined in Section 4(b)) and prior to the date the Registration Statement
filed pursuant to Section 4(b) hereof is declared effective by the SEC, and (D)
during which sales of any Registrable Securities cannot be made pursuant to any
such Registration Statement after the Registration Statement has been declared
effective or the Common Stock is not listed or included for quotation on the
NNM, SmallCap, NYSE or AMEX; provided, however, that there shall be excluded
from each such period any delays which are solely attributable to changes (other
than corrections of Company mistakes with respect to information previously
provided by the Investors) required by the Investors in the Registration
Statement with respect to information relating to the Investors, including,
without limitation, changes to the plan of distribution. Notwithstanding the
foregoing, in no event shall the Company be required to pay amounts with respect
to (x) both (A) and (B), and (y) both (C) and (D) above for the same period of
time. (For example, if the Registration Statement is not effective by the
applicable Registration Deadline, the Company would pay $20,000 for each thirty
(30) day period thereafter with respect to each $1,000,000 of Aggregate Share
Price until the Registration Statement becomes effective.) Such amounts shall be
paid in cash. Payments of cash pursuant hereto shall be made within five (5)
days after the end of each period that gives rise to such obligation, provided
that, if any such period extends for more than thirty (30) days, interim
payments shall be made for each such thirty (30) day period. The requirement to
make payments pursuant to this section can be waived as to all Investors
entitled to a given payment by the written consent of such Investors holding a
majority of the Registrable Securities held by all such Investors.



                                       4
<PAGE>

               (c) Piggy-Back Registrations. If at any time prior to the
expiration of the Registration Period (as hereinafter defined) the Company shall
file with the SEC a Registration Statement relating to an offering for its own
account or the account of others under the Securities Act of any of its equity
securities (other than on Form S-4 or Form S-8 or their then equivalents
relating to equity securities to be issued solely in connection with any
acquisition of any entity or business or equity securities issuable in
connection with stock option or other employee benefit plans), the Company shall
send to each Investor written notice of such determination and, if within
fifteen (15) days after the date of such notice, such Investor shall so request
in writing, the Company shall include in such Registration Statement all or any
part of the Registrable Securities such Investor requests to be registered,
except that if, in connection with any underwritten public offering, the
managing underwriter(s) thereof shall impose a limitation on the number of
shares of Common Stock which may be included in the Registration Statement
because, in such underwriter(s)' judgment, marketing or other factors dictate
such limitation is necessary to facilitate public distribution, then the Company
shall be obligated to include in such Registration Statement only such limited
portion of the Registrable Securities with respect to which such Investor has
requested inclusion hereunder as the underwriter shall permit. Any exclusion of
Registrable Securities shall be made pro rata among the Investors seeking to
include Registrable Securities, in proportion to the number of Registrable
Securities sought to be included by such Investors; provided, however, that the
Company shall not exclude any Registrable Securities unless the Company has
first excluded all outstanding securities, the holders of which are not
contractually entitled to inclusion of such securities in such Registration
Statement or are not contractually entitled to pro rata inclusion with the
Registrable Securities; and provided, further, however, that, after giving
effect to the immediately preceding proviso, any exclusion of Registrable
Securities shall be made pro rata with holders of other securities having the
contractual right to include such securities in the Registration Statement other
than holders of securities contractually entitled to inclusion of their
securities in such Registration Statement by reason of demand registration
rights. Notwithstanding the foregoing, no such reduction shall reduce the amount
of Registrable Securities included in the registration below twenty-five (25%)
of the total amount of securities included in such registration. No right to
registration of Registrable Securities under this Section 2(c) shall be
construed to limit any registration required under Section 2(a) hereof. If an
offering in connection with which an Investor is entitled to registration under
this Section 2(c) is an underwritten offering, then each Investor whose
Registrable Securities are included in such Registration Statement shall, unless
otherwise agreed by the Company, offer and sell such Registrable Securities in
an underwritten offering using the same underwriter or underwriters and, subject
to the provisions of this Agreement, on the same terms and conditions as other
shares of Common Stock included in such underwritten offering.

               (d) Eligibility for Form S-3. The Company represents and warrants
that it meets the requirements for the use of Form S-3 for registration of the
sale by the Initial Investors and any other Investor of the Registrable
Securities and the Company shall file all reports required to be filed by the
Company with the SEC in a timely manner so as to maintain such eligibility for
the use of Form S-3.

               (e) Registrable Securities Not Permitted to be Included on
Registration Statement. Notwithstanding any other provision in this Agreement to
the contrary, in the event that the Company is prohibited by the Securities Act
and the Rules promulgated thereunder (including as a result of the
interpretation thereof by the SEC) from including any Registrable Securities on
a



                                       5
<PAGE>

Registration Statement that would otherwise be required to be included on such
Registration Statement by operation of this Agreement, after having used its
best efforts to have such Registrable Securities so included, then the Company
shall be permitted to exclude such Registrable Securities (but only such
Registrable Securities) from such Registration Statement, and such exclusion
shall not alone constitute a breach of this Agreement; provided, however, that
the Company shall be required, pursuant to Section 4(b) below, to register such
Registrable Securities (either by the amendment of the existing applicable
Registration Statement or the filing of a new Registration Statement) upon such
prohibition no longer being applicable to such Registrable Securities.

        3. DELAY PERIODS; SUSPENSION OF SALES.

               (a) Delay Period. If, at any time prior to the expiration of the
Registration Period (as defined below), in the good faith reasonable judgment of
the Company's Board of Directors, the disposition of Registrable Securities
would require the premature disclosure of material non-public information which
may reasonably be expected to have an adverse effect on the Company, then the
Company shall not be required to maintain the effectiveness of or amend or
supplement the Registration Statement for a period (a "DISCLOSURE DELAY PERIOD")
expiring upon the earlier to occur of (i) the date on which such material
information is disclosed to the public or ceases to be material or (ii) subject
to Section 3(b) hereof, up to ten (10) trading days after the date on which the
Company provides a notice to the Investors under Section 4(e) hereof stating
that the failure to disclose such non-public information causes the prospectus
included in the Registration Statement, as then in effect, to include an untrue
statement of a material fact or to omit to state a material fact required to be
stated therein or necessary to make the statements therein not misleading (each,
a "DISCLOSURE DELAY PERIOD NOTICE"). For the avoidance of doubt, in no event
shall a Disclosure Delay Period exceed ten (10) trading days.

               (b) The Company will give prompt written notice, in the manner
prescribed by Section 12 hereof, to the Investors of each Disclosure Delay
Period. If practicable, such notice shall estimate the duration of such
Disclosure Delay Period. Each Investor agrees that, upon receipt of a Disclosure
Delay Period Notice prior to the Investor's disposition of all such Registrable
Securities, the Investor will forthwith discontinue the disposition of such
Registrable Securities pursuant to the Registration Statement, and will not
deliver any prospectus forming a part thereof in connection with any sale of
such Registrable Securities until the expiration of such Disclosure Delay
Period. In addition, the provisions of Section 2(b) hereof shall not apply to
the Disclosure Delay Periods. Notwithstanding anything in this Section 3 to the
contrary, the Company shall not deliver more than two (2) Disclosure Delay
Period Notices in any one (1) year period and there shall not be more than an
aggregate of sixty (60) calendar days in any twelve (12) month period during
which the Company is in a Disclosure Delay Period nor more than an aggregate of
thirty (30) calendar days in any ninety (90) calendar day period during which
the Company is in a Disclosure Delay Period.

        4. OBLIGATIONS OF THE COMPANY.

        In connection with the registration of the Registrable Securities, the
Company shall have the following obligations:



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               (a) The Company shall respond promptly to any and all comments
made by the staff of the SEC to the Registration Statements required by Section
2(a), and shall submit to the SEC before the close of business on or before the
second business day immediately following the business day on which the Company
learns (either by telephone or in writing) that no review of such Registration
Statements will be made by the SEC or that the staff of the SEC has no further
comments on such Registration Statements, as the case may be, a request for
acceleration of the effectiveness of such Registration Statements to a time and
date as soon as practicable. The Company shall keep each such Registration
Statement effective pursuant to Rule 415 at all times until such date as is the
earlier of (i) the date on which all of the Registrable Securities covered
thereby have been sold and (ii) the date on which all of the Registrable
Securities covered thereby may be immediately sold to the public without
registration or restriction pursuant to Rule 144(k) under the Securities Act or
any successor provision (the "REGISTRATION PERIOD"), which Registration
Statements (including any amendments or supplements thereto and prospectuses
contained therein and all documents incorporated by reference therein) (i) shall
comply in all material respects with the requirements of the Securities Act and
the rules and regulations of the SEC promulgated thereunder and (ii) shall not
contain any untrue statement of a material fact or omit to state a material fact
required to be stated therein, or necessary to make the statements therein not
misleading. The financial statements of the Company included in the Registration
Statements or incorporated by reference therein will comply as to form in all
material respects with the applicable accounting requirements and the published
rules and regulations of the SEC applicable with respect thereto. Such financial
statements will be prepared in accordance with U.S. generally accepted
accounting principles, consistently applied, during the periods involved (except
(i) as may be otherwise indicated in such financial statements or the notes
thereto, or (ii) in the case of unaudited interim statements, to the extent they
may not include footnotes or may be condensed on summary statements and fairly
present in all material respects the consolidated financial position of the
Company and its consolidated subsidiaries as of the dates thereof and the
consolidated results of their operations and cash flows for the periods then
ended (subject, in the case of unaudited statements, to immaterial year-end
adjustments)).

               (b) The Company shall use its best efforts, to prepare and file
with the SEC such amendments (including post-effective amendments) and
supplements to the Registration Statements and the prospectus used in connection
with the Registration Statements as may be necessary to keep the Registration
Statements effective at all times during the applicable Registration Period,
and, during such period, comply with the provisions of the Securities Act with
respect to the disposition of all Registrable Securities of the Company covered
by the Registration Statements until such time as all of such Registrable
Securities have been disposed of in accordance with the intended methods of
disposition by the seller or sellers thereof as set forth in the Registration
Statements. In the event the number of shares available under any Registration
Statement filed pursuant to this Agreement is, for any three (3) consecutive
trading days (the last of such three (3) trading days being the "REGISTRATION
TRIGGER DATE"), insufficient to cover one hundred percent (100%) of the
Registrable Securities issued or issuable upon conversion (without giving effect
to any limitations on conversion contained in Article IV.D of the Certificate of
Designation) of the Preferred Stock and exercise of the Warrants (without giving
effect to any limitations on exercise contained in Section 7(g) of the Warrants)
and required to be included thereon, the Company shall amend the applicable
Registration Statement, or file a new Registration Statement (on the short form
available therefor, if applicable),



                                       7
<PAGE>

or both, so as to cover one hundred percent (100%) of the Registrable Securities
issued or issuable (without giving effect to any limitations on conversion or
exercise contained in the Certificate of Designation or the Warrants) as of the
Registration Trigger Date, in each case, as soon as practicable, but in any
event within fifteen (15) days after the Registration Trigger Date (based on the
market price then in effect of the Common Stock and other relevant factors on
which the Company reasonably elects to rely). The Company shall use its best
efforts to cause such amendment(s) and/or new Registration Statement to become
effective as soon as practicable following the filing thereof. In the event the
Company fails to obtain the effectiveness of any such Registration Statement
within sixty (60) days after a Registration Trigger Date, each Investor shall
thereafter have the option, exercisable in whole or in part at any time and from
time to time by delivery of a written notice to the Company (a "MANDATORY
REDEMPTION NOTICE"), to require the Company to purchase for cash, at an amount
per share equal to the Redemption Amount (as defined in Article VIII.B of the
Certificate of Designation), a portion of the Investor's Preferred Stock such
that the total number of Registrable Securities included on the Registration
Statements for resale by such Investor exceeds 100% of the Registrable
Securities issued or issuable upon conversion (without giving effect to any
limitations on conversion contained in Article IV.D of the Certificate of
Designation) of such Investor's Preferred Stock and exercise of such Investor's
Warrants. If the Corporation fails to redeem any of such shares within five (5)
business days after its receipt of a Mandatory Redemption Notice, then such
Investor shall be entitled to the remedies provided in Article VIII.D of the
Certificate of Designation.

               (c) The Company shall furnish to each Investor whose Registrable
Securities are included in a Registration Statement and its legal counsel (i)
promptly after the same is prepared and publicly distributed, filed with the
SEC, or received by the Company, one copy of the Registration Statement and any
amendment thereto, each preliminary prospectus and prospectus and each amendment
or supplement thereto, and, in the case of one of the Registration Statements
referred to in Section 2(a), each letter written by or on behalf of the Company
to the SEC or the staff of the SEC (including, without limitation, any request
to accelerate the effectiveness of the Registration Statement or amendment
thereto), and each item of correspondence from the SEC or the staff of the SEC,
in each case relating to the Registration Statement (other than any portion, if
any, thereof which contains information for which the Company has sought
confidential treatment), (ii) by the next business day after the date of
effectiveness of the Registration Statement or any amendment thereto, a notice
stating that the Registration Statement or amendment has been declared
effective, and (iii) such number of copies of a prospectus, including a
preliminary prospectus, and all amendments and supplements thereto and such
other documents as such Investor may reasonably request in order to facilitate
the disposition of the Registrable Securities owned by such Investor.

               (d) The Company shall use its best efforts to (i) register and
qualify the Registrable Securities covered by the Registration Statements under
such other securities or "blue sky" laws of such jurisdictions in the United
States as each Investor who holds Registrable Securities being offered
reasonably requests, (ii) prepare and file in those jurisdictions such
amendments (including post-effective amendments) and supplements to such
registrations and qualifications as may be necessary to maintain the
effectiveness thereof during the applicable Registration Period, (iii) take such
other actions as may be necessary to maintain such registrations and
qualifications in effect at all times during the applicable Registration Period,
and (iv) take all other actions reasonably necessary or advisable to qualify the
Registrable Securities for sale in such jurisdictions; provided, however, that
the Company shall not be required in connection therewith or as a condition
thereto to



                                       8
<PAGE>

(a) qualify to do business in any jurisdiction where it would not otherwise be
required to qualify but for this Section 4(d), (b) subject itself to general
taxation in any such jurisdiction, (c) file a general consent to service of
process in any such jurisdiction, (d) provide any undertakings that cause the
Company undue expense or burden, or (e) make any change in its charter or
bylaws, which in each case the Board of Directors of the Company determines to
be contrary to the best interests of the Company and its stockholders.

               (e) As promptly as practicable after becoming aware of such
event, the Company shall notify each Investor by telephone and facsimile of the
happening of any event, of which the Company has knowledge, as a result of which
the prospectus included in a Registration Statement, as then in effect, includes
an untrue statement of a material fact or omission to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading, and, use its best efforts promptly to prepare a supplement or
amendment to the Registration Statement to correct such untrue statement or
omission, and deliver such number of copies of such supplement or amendment to
each Investor as such Investor may reasonably request.

               (f) The Company shall use its best efforts (i) to prevent the
issuance of any stop order or other suspension of effectiveness of a
Registration Statement (other than as permitted herein), and, if such an order
is issued, to obtain the withdrawal of such order at the earliest practicable
moment (including in each case by amending or supplementing such Registration
Statement) and (ii) to notify each Investor who holds Registrable Securities
being sold (or, in the event of an underwritten offering, the managing
underwriters) of the issuance of such order and the resolution thereof (and if
such Registration Statement is supplemented or amended, deliver such number of
copies of such supplement or amendment to each Investor as such Investor may
reasonably request).

               (g) The Company shall permit a single firm of counsel designated
by the Initial Investors to review the Registration Statements and all
amendments and supplements thereto a reasonable period of time prior to its
filing with the SEC, and not file any document in a form to which such counsel
reasonably objects.

               (h) The Company shall make generally available to its security
holders as soon as practical, but not later than ninety (90) days after the
close of the period covered thereby, an earnings statement (in form complying
with the provisions of Rule 158 under the Securities Act) covering a
twelve-month period beginning not later than the first day of the Company's
fiscal quarter next following the effective date of the Registration Statement
required to be filed pursuant to Section 2(a)(i), which compliance will be met
through the Company's filing, on an appropriate form, the appropriate report of
the Company as required by the Securities Exchange Act of 1934, as amended.

               (i) The Company shall hold in confidence and not make any
disclosure of information concerning an Investor provided to the Company unless
(i) disclosure of such information is necessary to comply with federal or state
securities laws, (ii) the disclosure of such information is necessary to avoid
or correct a misstatement or omission in any Registration Statement, (iii) the
release of such information is ordered pursuant to a subpoena or other order
from a court or governmental body of competent jurisdiction, (iv) such
information has been made generally available to the public other than by
disclosure in violation of this or any other agreement,



                                       9
<PAGE>

or (v) such Investor consents to the form and content of any such disclosure.
The Company agrees that it shall, upon learning that disclosure of such
information concerning an Investor is sought in or by a court or governmental
body of competent jurisdiction or through other means, give prompt notice to
such Investor prior to making such disclosure, and allow the Investor, at its
expense, to undertake appropriate action to prevent disclosure of, or to obtain
a protective order for, such information.

               (j) The Company shall use its best efforts to promptly either (i)
cause all of the Registrable Securities covered by any Registration Statement to
be listed on the NYSE or the AMEX or another national securities exchange and on
each additional national securities exchange on which securities of the same
class or series issued by the Company are then listed, if any, if the listing of
such Registrable Securities is then permitted under the rules of such exchange,
or (ii) secure the designation and quotation of all of the Registrable
Securities covered by any Registration Statement on the NNM or SmallCap and,
without limiting the generality of the foregoing, to arrange for or maintain at
least two market makers to register with the National Association of Securities
Dealers, Inc. ("NASD") as such with respect to such Registrable Securities.

               (k) The Company shall provide a transfer agent and registrar,
which may be a single entity, for the Registrable Securities not later than the
effective date of the Registration Statement.

               (l) The Company shall cooperate with the Investors who hold
Registrable Securities being offered to facilitate the timely preparation and
delivery of certificates (not bearing any restrictive legends to the extent
permitted by the Securities Purchase Agreement or Exchange Agreement, as
applicable) representing Registrable Securities to be offered pursuant to the
Registration Statements and enable such certificates to be in such denominations
or amounts, as the case may be, as the Investors may reasonably request and
registered in such names as the Investors may request.

               (m) At the request of any Investor, the Company shall prepare and
file with the SEC such amendments (including post-effective amendments) and
supplements to a Registration Statement and the prospectus used in connection
with such Registration Statement as may be necessary in order to change the plan
of distribution set forth in such Registration Statement.

               (n) The Company shall comply with all applicable laws related to
a Registration Statement and offering and sale of securities and all applicable
rules and regulations of governmental authorities in connection therewith
(including, without limitation, the Securities Act and the Securities Exchange
Act of 1934, as amended, and the rules and regulations promulgated by the SEC).

               (o) From and after the date of this Agreement, the Company shall
not, and shall not agree to, allow the holders of any securities of the Company
to include any of their securities which are not Registrable Securities in a
Registration Statement under Section 2(a) hereof or any amendment or supplement
thereto under Section 4(b) hereof without the consent of the holders of a
majority in interest of the Registrable Securities (other than as set forth in
the Schedule of Exceptions to the Securities Purchase Agreement and the Exchange
Agreement).



                                       10
<PAGE>

        5. OBLIGATIONS OF THE INVESTORS. In connection with the registration of
the Registrable Securities, the Investors shall have the following obligations:

               (a) It shall be a condition precedent to the obligations of the
Company to complete the registration pursuant to this Agreement with respect to
the Registrable Securities of a particular Investor that such Investor shall
furnish to the Company such information regarding itself, the Registrable
Securities held by it and the intended method of disposition of the Registrable
Securities held by it as shall be reasonably required to effect the registration
of such Registrable Securities and shall execute such documents in connection
with such registration as the Company may reasonably request. At least five
trading days prior to the first anticipated filing date of a Registration
Statement, the Company shall notify each Investor of the information the Company
requires from each such Investor.

               (b) Each Investor, by such Investor's acceptance of the
Registrable Securities, agrees to cooperate with the Company as reasonably
requested by the Company in connection with the preparation and filing of the
Registration Statements hereunder, unless such Investor has notified the Company
in writing of such Investor's election to exclude all of such Investor's
Registrable Securities from such Registration Statements.

               (c) Each Investor agrees that, upon receipt of any notice from
the Company of the happening of any event of the kind described in Sections 4(e)
or 3(a), such Investor will immediately discontinue disposition of Registrable
Securities pursuant to the Registration Statement covering such Registrable
Securities until such Investor's receipt of the copies of the supplemented or
amended prospectus contemplated by Sections 4(e) or 3(a) and, if so directed by
the Company, such Investor shall deliver to the Company (at the expense of the
Company) or destroy (and deliver to the Company a certificate of destruction)
all copies in such Investor's possession, of the prospectus covering such
Registrable Securities current at the time of receipt of such notice.
Notwithstanding anything to the contrary, subject to compliance with applicable
laws, the Company shall cause the transfer agent for the Registrable Securities
to deliver unlegended shares of Common Stock to a transferee of an Investor in
accordance with the terms of the Certificate of Designation and Warrants in
connection with any sale of Registrable Securities with respect to which such
Investor has entered into a contract for sale prior to receipt of such notice
and for which such Investor has not yet settled.



                                       11
<PAGE>

        6. EXPENSES OF REGISTRATION. All reasonable expenses incurred by the
Company or the Investors (but only for reasonable attorney's fees of one counsel
for the Investors) in connection with registrations, filings or qualifications
pursuant to Sections 2 and 4 above, including, without limitation, all
registration, listing and qualifications fees, printers and accounting fees, the
fees and disbursements of counsel for the Company, the fees and disbursements of
one counsel selected by the Investors, and the underwriting discounts and
commissions, shall be borne by the Company. In addition, the Company shall pay
all of the Investors' reasonable costs and expenses (including legal fees)
incurred in connection with the enforcement of the rights of the Investors
hereunder.

        7. INDEMNIFICATION. In the event any Registrable Securities are included
in a Registration Statement under this Agreement:

               (a) To the extent permitted by law, the Company will indemnify,
hold harmless and defend (i) each Investor who holds such Registrable
Securities, and (ii) the directors, officers, partners, members, employees and
agents of such Investor and each person who controls any Investor within the
meaning of Section 15 of the Securities Act or Section 20 of the Securities
Exchange Act of 1934, as amended (the "EXCHANGE ACT"), if any, (each, an
"INDEMNIFIED PERSON"), against any joint or several losses, claims, damages,
liabilities or expenses (collectively, together with actions, proceedings or
inquiries by any regulatory or self-regulatory organization, whether commenced
or threatened, in respect thereof, "CLAIMS") to which any of them may become
subject insofar as such Claims arise out of or are based upon: (i) any untrue
statement or alleged untrue statement of a material fact in a Registration
Statement or the omission or alleged omission to state therein a material fact
required to be stated or necessary to make the statements therein not
misleading, (ii) any untrue statement or alleged untrue statement of a material
fact contained in any preliminary prospectus if used prior to the effective date
of such Registration Statement, or contained in the final prospectus (as amended
or supplemented, if the Company files any amendment thereof or supplement
thereto with the SEC) or the omission or alleged omission to state therein any
material fact necessary to make the statements made therein, in light of the
circumstances under which the statements therein were made, not misleading, or
(iii) any violation or alleged violation by the Company of the Securities Act,
the Exchange Act, any other law, including, without limitation, any state
securities law, or any rule or regulation thereunder relating to the offer or
sale of the Registrable Securities (the matters in the foregoing clauses (i)
through (iii) being, collectively, "VIOLATIONS"). Subject to the restrictions
set forth in Section 7(c) with respect to the number of legal counsel, the
Company shall reimburse the Investors and each other Indemnified Person,
promptly as such expenses are incurred and are due and payable, for any
reasonable legal fees or other reasonable expenses incurred by them in
connection with investigating or defending any such Claim. Notwithstanding
anything to the contrary contained herein, the indemnification agreement
contained in this Section 7(a): (i) shall not apply to a Claim arising out of or
based upon a Violation which occurs in reliance upon and in conformity with
information furnished in writing to the Company by such Indemnified Person
expressly for use in the Registration Statement or any such amendment thereof or
supplement thereto; (ii) shall not apply to amounts paid in settlement of any
Claim if such settlement is effected without the prior written consent of the
Company, which consent shall not be unreasonably withheld; and (iii) with
respect to any preliminary prospectus, shall not inure to the benefit of any
Indemnified Person if the untrue statement or omission of material fact
contained in the preliminary prospectus was corrected on a timely basis in the
prospectus, as then amended or



                                       12
<PAGE>

supplemented, if such corrected prospectus was timely made available by the
Company pursuant to Section 4(c) hereof, and the Indemnified Person was promptly
advised in writing not to use the incorrect prospectus prior to the use giving
rise to a Violation and such Indemnified Person, notwithstanding such advice,
used it. Such indemnity shall remain in full force and effect regardless of any
investigation made by or on behalf of the Indemnified Person and shall survive
the transfer of the Registrable Securities by the Investors pursuant to Section
10 hereof.

               (b) In connection with any Registration Statement in which an
Investor is participating, each such Investor agrees severally and not jointly
to indemnify, hold harmless and defend, to the same extent and in the same
manner set forth in Section 7(a), the Company, each of its directors, each of
its officers who signs the Registration Statement, its employees, agents and
each person, if any, who controls the Company within the meaning of Section 15
of the Securities Act or Section 20 of the Exchange Act, and any other
stockholder selling securities pursuant to the Registration Statement or any of
its directors or officers or any person who controls such stockholder within the
meaning of the Securities Act or the Exchange Act (collectively and together
with an Indemnified Person, an "INDEMNIFIED PARTY"), against any Claim to which
any of them may become subject, under the Securities Act, the Exchange Act or
otherwise, insofar as such Claim arises out of or is based upon any Violation,
in each case to the extent (and only to the extent) that such Violation occurs
in reliance upon and in conformity with written information furnished to the
Company by such Investor expressly for use in connection with such Registration
Statement; and subject to Section 7(c) such Investor will reimburse any legal or
other expenses (promptly as such expenses are incurred and are due and payable)
reasonably incurred by them in connection with investigating or defending any
such Claim; provided, however, that the indemnity agreement contained in this
Section 7(b) shall not apply to amounts paid in settlement of any Claim if such
settlement is effected without the prior written consent of such Investor, which
consent shall not be unreasonably withheld; provided, further, however, that the
Investor shall be liable under this Agreement (including this Section 7(b) and
Section 8) for only that amount as does not exceed the net proceeds actually
received by such Investor as a result of the sale of Registrable Securities
pursuant to such Registration Statement. Such indemnity shall remain in full
force and effect regardless of any investigation made by or on behalf of such
Indemnified Party and shall survive the transfer of the Registrable Securities
by the Investors pursuant to Section 10 hereof. Notwithstanding anything to the
contrary contained herein, the indemnification agreement contained in this
Section 7(b) with respect to any preliminary prospectus shall not inure to the
benefit of any Indemnified Party if the untrue statement or omission of material
fact contained in the preliminary prospectus was corrected on a timely basis in
the prospectus, as then amended or supplemented.

               (c) Promptly after receipt by an Indemnified Person or
Indemnified Party under this Section 7 of notice of the commencement of any
action (including any governmental action), such Indemnified Person or
Indemnified Party shall, if a Claim in respect thereof is to made against any
indemnifying party under this Section 7, deliver to the indemnifying party a
written notice of the commencement thereof, and the indemnifying party shall
have the right to participate in, and, to the extent the indemnifying party so
desires, jointly with any other indemnifying party similarly noticed, to assume
control of the defense thereof with counsel mutually satisfactory to the
indemnifying party and the Indemnified Person or the Indemnified Party, as the
case may be; provided, however, that such indemnifying party shall not be
entitled to assume such defense and an Indemnified Person or Indemnified Party
shall have the right to retain its own counsel with the fees and expenses to be
paid



                                       13
<PAGE>

by the indemnifying party, if, in the reasonable opinion of counsel retained by
the indemnifying party, the representation by such counsel of the Indemnified
Person or Indemnified Party and the indemnifying party would be inappropriate
due to actual or potential conflicts of interest between such Indemnified Person
or Indemnified Party and any other party represented by such counsel in such
proceeding or the actual or potential defendants in, or targets of, any such
action include both the Indemnified Person or the Indemnified Party and the
indemnifying party and any such Indemnified Person or Indemnified Party
reasonably determines that there may be legal defenses available to such
Indemnified Person or Indemnified Party which are in conflict with those
available to such indemnifying party. The indemnifying party shall pay for only
one separate legal counsel for the Indemnified Persons or the Indemnified
Parties, as applicable, and such legal counsel shall be selected by Investors
holding a majority-in-interest of the Registrable Securities included in the
Registration Statement to which the Claim relates (with the approval of the
Initial Investors if it holds Registrable Securities included in such
Registration Statement), if the Investors are entitled to indemnification
hereunder, or by the Company, if the Company is entitled to indemnification
hereunder, as applicable. The failure to deliver written notice to the
indemnifying party within a reasonable time of the commencement of any such
action shall not relieve such indemnifying party of any liability to the
Indemnified Person or Indemnified Party under this Section 7, except to the
extent that the indemnifying party is actually prejudiced in its ability to
defend such action. The indemnification required by this Section 7 shall be made
by periodic payments of the amount thereof during the course of the
investigation or defense, as such expense, loss, damage or liability is incurred
and is due and payable.

        8. CONTRIBUTION. To the extent any indemnification by an indemnifying
party is prohibited or limited by law, the indemnifying party agrees to make the
maximum contribution with respect to any amounts for which it would otherwise be
liable under Section 7 to the fullest extent permitted by law as is appropriate
to reflect the relative fault of the indemnifying party, on the one hand, and
the Indemnified Person or Indemnified Party, as the case may be, on the other
hand, with respect to the Violation giving rise to the applicable Claim;
provided, however, that (i) no contribution shall be made under circumstances
where the maker would not have been liable for indemnification under the fault
standards set forth in Section 7, (ii) no person guilty of fraudulent
misrepresentation (within the meaning of Section 12(f) of the Securities Act)
shall be entitled to contribution from any seller of Registrable Securities who
was not guilty of such fraudulent misrepresentation, and (iii) contribution
(together with any indemnification or other obligations under this Agreement) by
any seller of Registrable Securities shall be limited in amount to the net
amount of proceeds received by such seller from the sale of such Registrable
Securities.

        9. REPORTS UNDER THE EXCHANGE ACT. With a view to making available to
the Investors the benefits of Rule 144 promulgated under the Securities Act or
any other similar rule or regulation of the SEC that may at any time permit the
Investors to sell securities of the Company to the public without registration
("RULE 144"), the Company agrees to:

                      (i) file with the SEC in a timely manner and make and keep
available all reports and other documents required of the Company under the
Securities Act and the Exchange Act so long as the Company remains subject to
such requirements (it being understood that nothing herein shall limit the
Company's obligations under Section 4(c) of the Securities Purchase Agreement



                                       14
<PAGE>

or the Exchange Agreement, as applicable) and the filing and availability of
such reports and other documents is required for the applicable provisions of
Rule 144; and

                      (ii) furnish to each Investor so long as such Investor
owns shares of Preferred Stock, Warrants or Registrable Securities, promptly
upon request, (i) a written statement by the Company that it has complied with
the reporting requirements of Rule 144, the Securities Act and the Exchange Act,
(ii) a copy of the most recent annual or quarterly report of the Company and
such other reports and documents so filed by the Company, and (iii) such other
information as may be reasonably requested to permit the Investors to sell such
securities under Rule 144 without registration.

        10. ASSIGNMENT OF REGISTRATION RIGHTS. The rights of the Investors
hereunder, including the right to have the Company register Registrable
Securities pursuant to this Agreement, shall be automatically assignable by each
Investor to any transferee of all or any portion of the shares of Preferred
Stock, the Warrants or the Registrable Securities if: (i) the Investor agrees in
writing with the transferee or assignee to assign such rights, and a copy of
such agreement is furnished to the Company after such assignment, (ii) the
Company is furnished with written notice of (a) the name and address of such
transferee or assignee, and (b) the securities with respect to which such
registration rights are being transferred or assigned, (iii) following such
transfer or assignment, the further disposition of such securities by the
transferee or assignee is restricted under the Securities Act and applicable
state securities laws, (iv) the transferee or assignee agrees in writing for the
benefit of the Company to be bound by all of the provisions contained herein,
and (v) such transfer shall have been made in accordance with the applicable
requirements of the Securities Purchase Agreement, the Exchange Agreement, the
Certificate of Designation for the Preferred Stock, the Warrants and the Notes,
as applicable. In addition, and notwithstanding anything to the contrary
contained in this Agreement, the Securities Purchase Agreement, the Exchange
Agreement, the Certificate of Designation, the Warrants or the Notes, the
Securities (as defined in the Securities Purchase Agreement and the Exchange
Agreement) may be pledged, and all rights of the Investors under this Agreement
or any other agreement or document related to the transactions contemplated
hereby may be assigned, without further consent of the Company, to a bona fide
pledgee in connection with an Investor's margin or brokerage account.

        11. AMENDMENT OF REGISTRATION RIGHTS. Provisions of this Agreement may
be amended and the observance thereof may be waived (either generally or in a
particular instance and either retroactively or prospectively), only with
written consent of the Company, and Investors who hold a majority of the
Registrable Securities or, in the case of a waiver, with the written consent of
the party charged with the enforcement of any such provision; provided, however,
that no consideration shall be paid to an Investor by the Company in connection
with an amendment hereto unless each Investor similarly affected by such
amendment receives a pro-rata amount of consideration from the Company. Any
amendment or waiver effected in accordance with this Section 11 shall be binding
upon each Investor and the Company.

        12. MISCELLANEOUS.

               (a) A person or entity is deemed to be a holder of Registrable
Securities whenever such person or entity owns of record such Registrable
Securities. If the Company receives



                                       15
<PAGE>

conflicting instructions, notices or elections from two or more persons or
entities with respect to the same Registrable Securities, the Company shall act
upon the basis of instructions, notice or election received from the registered
owner of such Registrable Securities.

               (b) Any notices required or permitted to be given under the terms
of this Agreement shall be sent by certified or registered mail (return receipt
requested), or by a nationally recognized overnight delivery service, or
delivered personally or by courier or by confirmed telecopy, and shall be
effective five (5) days after being placed in the mail, if mailed certified or
registered mailed, or one (1) day after being delivered to the nationally
recognized overnight delivery service, if delivered in such manner, or upon
receipt or refusal of receipt, if delivered personally or by courier or
confirmed telecopy, in each case addressed to a party. The addresses for such
communications shall be:

                      If to the Company:

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

                      with a copy simultaneously transmitted by like means to:

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

and if to any Investor, at such address as such Investor shall have provided in
writing to the Company, or at such other address as each such party furnishes by
notice given in accordance with this Section 12(b).

               (c) Failure of any party to exercise any right or remedy under
this Agreement or otherwise, or delay by a party in exercising such right or
remedy, shall not operate as a waiver thereof.

               (d) This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware applicable to contracts made
and to be performed in the State of Delaware. The Company irrevocably consents
to the jurisdiction of the United States federal courts and the state courts
located in the State of Delaware in any suit or proceeding based on or arising
under this Agreement and irrevocably agrees that all claims in respect of such
suit or proceeding may be determined in such courts. The Company irrevocably
waives the defense of an inconvenient forum to the maintenance of such suit or
proceeding. The Company further agrees that service of process upon the Company,
mailed by first class mail shall be deemed in every respect effective service of
process upon the Company in any such suit or proceeding. Nothing herein shall
affect the Investors' right to serve process in any other manner permitted by
law. The Company agrees that a



                                       16
<PAGE>

final non-appealable judgment in any such suit or proceeding shall be conclusive
and may be enforced in other jurisdictions by suit on such judgment or in any
other lawful manner.

               (e) This Agreement, the Securities Purchase Agreement (including
all schedules and exhibits thereto), the Exchange Agreement (including all
schedules and exhibits thereto), the Warrants, the Notes and the Security
Documents (as defined in the Exchange Agreement) constitute the entire agreement
among the parties hereto with respect to the subject matter hereof and thereof.
There are no restrictions, promises, warranties or undertakings, other than
those set forth or referred to herein and therein. This Agreement, the
Securities Purchase Agreement, the Exchange Agreement, the Warrants, the Notes
and the Security Documents supersede all prior agreements and understandings
among the parties hereto with respect to the subject matter hereof and thereof.

               (f) Subject to the requirements of Section 10 hereof, this
Agreement shall inure to the benefit of and be binding upon the successors and
assigns of each of the parties hereto.

               (g) The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

               (h) This Agreement may be executed in two or more counterparts,
each of which shall be deemed an original but all of which shall constitute one
and the same agreement. This Agreement, once executed by a party, may be
delivered to the other party hereto by facsimile transmission of a copy of this
Agreement bearing the signature of the party so delivering this Agreement.

               (i) Each party shall do and perform, or cause to be done and
performed, all such further acts and things, and shall execute and deliver all
such other agreements, certificates, instruments and documents, as the other
party may reasonably request in order to carry out the intent and accomplish the
purposes of this Agreement and the consummation of the transactions contemplated
hereby.

               (j) All consents, approvals and other determinations to be made
by the Investors pursuant to this Agreement shall be made by the Investors
holding a majority in interest of the Registrable Securities (determined as if
all shares of Preferred Stock and Warrants then outstanding had been converted
into or exercised for Registrable Securities) held by all Investors.

               (k) The initial number of Registrable Securities included on any
Registration Statement and each increase to the number of Registrable Securities
included thereon shall be allocated pro rata among the Investors based on the
number of Registrable Securities held by each Investor at the time of such
establishment or increase, as the case may be, and required to be included on
such Registration Statement. In the event an Investor shall sell or otherwise
transfer any of such holder's Registrable Securities, each transferee shall be
allocated a pro rata portion of the number of Registrable Securities included on
a Registration Statement for such transferor. Any shares of Common Stock
included on a Registration Statement and which remain allocated to any person or
entity which does not hold any Registrable Securities shall be allocated to the
remaining Investors, pro rata based on the number of shares of Registrable
Securities then held by such Investors. For the avoidance of doubt, the number
of Registrable Securities held by any Investor



                                       17
<PAGE>

shall be determined as if all shares of Preferred Stock and Warrants then
outstanding were converted into or exercised for Registrable Securities.

               (l) Each party to this Agreement has participated in the
negotiation and drafting of this Agreement. As such, the language used herein
shall be deemed to be the language chosen by the parties hereto to express their
mutual intent, and no rule of strict construction will be applied against any
party to this Agreement.

               (m) For purposes of this Agreement, the term "business day" means
any day other than a Saturday or Sunday or a day on which banking institutions
in the State of New York are authorized or obligated by law, regulation or
executive order to close, and the term "trading day" means any day on which NNM,
or if the Common Stock is not then traded on NNM the principal securities
exchange or trading market where the Common Stock is then listed or traded, is
open for trading.



                                       18
<PAGE>

        IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed as of the date first above written.


VIROLOGIC, INC.

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

INITIAL INVESTORS:

[PURCHASER]


By:
   --------------------------------
   Name:
   Title:



                                       19