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                                                                     EXHIBIT 4.3



                                VIROLOGIC, INC.
                           SECOND AMENDED AND RESTATED
                           INVESTORS' RIGHTS AGREEMENT

        THIS INVESTORS' RIGHTS AGREEMENT (the "AGREEMENT") is made and entered
into as of the 23rd day of August, 1999 by and among VIROLOGIC, INC., a Delaware
corporation (the "Company"), and the persons and entities identified on Schedule
1 attached hereto (the "HOLDERS"). This Agreement supersedes and replaces the
Company's Amended and Restated Investors' Rights Agreement dated August 25, 1998
(the "PRIOR INVESTORS' RIGHTS AGREEMENT").

                                    RECITALS

        WHEREAS, on May 23, 1996, the Company entered into a Series A Preferred
Stock Purchase Agreement (the "SERIES A AGREEMENT") and issued shares of Series
A Preferred Stock to the persons and entities on Exhibit A thereto;

        WHEREAS, simultaneously with the Series A Agreement, the Company entered
into an Investors' Rights Agreement with the persons and entities listed on
Exhibit A to the Investors' Rights Agreement;

        WHEREAS, on November 13, 1997, the holders of the Company's Series A
Preferred Stock elected to convert their Series A Preferred Stock to Common
Stock;

        WHEREAS, on August 25, 1998, the Company entered into a Series B
Preferred Stock Purchase Agreement (the "SERIES B AGREEMENT") and issued shares
of Series B Preferred Stock to the persons and entities on Exhibit A thereto;

        WHEREAS, simultaneously with the Series B Agreement, the Company entered
into an the Prior Investors' Rights Agreement with the persons and entities
listed on Exhibit A to the Prior Investors' Rights Agreement;

        WHEREAS, simultaneously herewith, the Company is entering into a Series
C Preferred Stock Purchase Agreement (the "SERIES C AGREEMENT") and issuing
shares of Series C Preferred Stock to the Investors named in Exhibit A to the
Series C Agreement; and

        WHEREAS, the Holders intend to waive the rights set forth in Section 3.4
of the Prior Investors' Rights Agreement in connection with the issuance of
shares of Series C Preferred Stock pursuant to the Series C Agreement.

        NOW, THEREFORE, it is hereby agreed as follows:

SECTION 1.

        1.1 CERTAIN DEFINITIONS. As used in this Agreement, the following terms
shall have the meanings set forth below:



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               (a) "COMMISSION" shall mean the Securities and Exchange
Commission or any other federal agency at the time administering the Securities
Act.

               (b) "EXCHANGE ACT" shall mean the Securities Exchange Act of
1934, as amended, or any similar successor federal statute and the rules and
regulations thereunder, all as the same shall be in effect from time to time.

               (c) "HOLDER" shall mean any Investor who holds Registrable
Securities and any holder of Registrable Securities to whom the registration
rights conferred by this Agreement have been transferred in compliance with
Section 2.11 hereof.

               (d) "INITIATING HOLDERS" shall mean any Holder or Holders who in
the aggregate hold not less than (i) thirty percent (30%) of the outstanding
Registrable Securities or (ii) any lesser number of Registrable Securities if
the anticipated aggregate offering price thereof would exceed ten million
dollars ($10,000,000).

               (e) "INVESTORS" shall mean persons who purchased Shares pursuant
to the Series A Agreement, the Series B Agreement or the Series C Agreement.

               (f) "OTHER STOCKHOLDERS" shall mean persons other than Holders
who, by virtue of agreements with the Company, are entitled to include their
securities in certain registrations hereunder.

               (g) "PREFERRED STOCK" shall mean the Company's Series B Preferred
Stock and the Company's Series C Preferred Stock.

               (h) "REGISTRABLE SECURITIES" shall mean (i) shares of Common
Stock issued or issuable pursuant to the conversion of the Shares and (ii) any
Common Stock issued as a dividend or other distribution with respect to or in
exchange for or in replacement of the shares referenced in (i) above, provided,
however, that Registrable Securities shall not include any shares of Common
Stock which have previously been registered or which have been sold to the
public.

               (i) The terms "REGISTER," "REGISTERED" and "REGISTRATION" shall
refer to a registration effected by preparing and filing a registration
statement in compliance with the Securities Act and applicable rules and
regulations thereunder, and the declaration or ordering of the effectiveness of
such registration statement.

               (j) "REGISTRATION EXPENSES" shall mean all expenses incurred in
effecting any registration pursuant to this Agreement, including, without
limitation, all registration, qualification, and filing fees, printing expenses,
escrow fees, fees and disbursements of counsel for the Company, blue sky fees
and expenses, and expenses of any regular or special audits incident to or
required by any such registration, but shall not include Selling Expenses and
fees and disbursements of counsel for the Holders (but excluding the
compensation of regular employees of the Company, which shall be paid in any
event by the Company).




                                       2.
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               (k) "RULE 144" shall mean Rule 144 as promulgated by the
Commission under the Securities Act, as such Rule may be amended from time to
time, or any similar successor rule that may be promulgated by the Commission.

               (l) "RULE 145" shall mean Rule 145 as promulgated by the
Commission under the Securities Act, as such Rule may be amended from time to
time, or any similar successor rule that may be promulgated by the Commission.

               (m) "SECURITIES ACT" shall mean the Securities Act of 1933, as
amended, or any similar successor federal statute and the rules and regulations
thereunder, all as the same shall be in effect from time to time.

               (n) "SELLING EXPENSES" shall mean all underwriting discounts and
selling commissions applicable to the sale of Registrable Securities and fees
and disbursements of counsel for any Holder (other than the fees and
disbursements of counsel included in Registration Expenses).

               (o) "SERIES A AGREEMENT" shall mean the Series A Preferred Stock
Purchase Agreement, dated May 23, 1996 between the Company and the investors
listed on Exhibit A thereto.

               (p) "SERIES B AGREEMENT" shall mean the Series B Preferred Stock
Purchase Agreement dated August 25, 1999 between the Company and the investors
listed on Exhibit A thereto.

               (q) "SERIES C AGREEMENT" shall mean the Series C Preferred Stock
Purchase Agreement dated the date hereof between the Company and the investors
listed on Exhibit A thereto.

               (r) "SHARES" shall mean the Company's Series A Preferred Stock,
Series B Preferred Stock and Series C Preferred Stock.

SECTION 2. REQUESTED REGISTRATION.

        2.1 REQUEST FOR REGISTRATION. If the Company shall receive from
Initiating Holders at any time or times not earlier than the earlier of (i)
December 31, 2000 or (ii) six months after the effective date of the first
registration statement filed by the Company covering an underwritten offering of
any of its securities to the general public, a written request that the Company
effect any registration with respect to all or a part of the Registrable
Securities, the Company will (X) promptly give written notice of the proposed
registration to all other Holders and (Y) as soon as practicable, use its best
efforts to effect such registration (including, without limitation, filing
post-effective amendments, appropriate qualifications under applicable blue sky
or other state securities laws, and appropriate compliance with the Securities
Act) and as would permit or facilitate the sale and distribution of all or such
portion of such Registrable Securities as are specified in such request,
together with all or such portion of the Registrable Securities of any Holder or
Holders joining in such request as are specified in a written request received
by the Company within twenty (20) days after such written notice from the
Company is mailed or



                                       3.
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delivered. Notwithstanding the foregoing, the Company shall not be obligated to
effect, or to take any action to effect, any such registration pursuant to this
Section 2.1:

                      (i) In any particular jurisdiction in which the Company
would be required to execute a general consent to service of process in
effecting such registration, qualification, or compliance, unless the Company is
already subject to service in such jurisdiction and except as may be required by
the Securities Act;

                      (ii) After the Company has either (x) in the event that
the Company is eligible for registration of Registrable Securities on Form S-3,
initiated two such registrations pursuant to this Section 2.1(a) (counting for
these purposes only registrations which have been declared or ordered effective
and pursuant to which securities have been sold and registrations which have
been withdrawn by the Holders as to which the Holders have not elected to bear
the Registration Expenses pursuant to Section 2.3 hereof and would, absent such
election, have been required to bear such expenses) or (y) in the event that the
Company is not eligible for registration of Registrable Securities on Form S-3,
initiated four such registrations pursuant to this Section 2.1(a) (counting for
these purposes only registrations which have been declared or ordered effective
and pursuant to which securities have been sold and registrations which have
been withdrawn by Holders as to which Holders have not elected to bear the
Registration Expenses pursuant to Section 2.3 hereof and would, absent such
election, have been required to bear such expenses), provided, however, that the
third and fourth registration pursuant to this Section 2.1(a) may not be made
within twelve months of each other; or

                      (iii) During the period starting with the date thirty (30)
days prior to the Company's good faith estimate of the date of filing of, and
ending on a date one hundred eighty (180) days after the effective date of, a
Company-initiated registration; provided that the Company is actively employing
in good faith all reasonable efforts to cause such registration statement to
become effective.

               (b) Subject to the foregoing clauses (i) through (iii), the
Company shall file a registration statement covering the Registrable Securities
so requested to be registered as soon as practicable after receipt of the
request or requests of the Initiating Holders; provided, however, that if (i) in
the good faith judgment of the Board of Directors of the Company, such
registration would be seriously detrimental (excluding any consideration of
market price fluctuation due to the sale of the Registrable Securities) to the
Company and the Board of Directors of the Company concludes, as a result, that
it is essential to defer the filing of such registration statement at such time,
and (ii) the Company shall furnish to such Holders a certificate signed by the
President of the Company stating that in the good faith judgment of the Board of
Directors of the Company, it would be seriously detrimental (excluding any
consideration of market price fluctuation due to the sale of the Registrable
Securities) to the Company for such registration statement to be filed in the
near future and that it is, therefore, essential to defer the filing of such
registration statement, then the Company shall have the right to defer such
filing for the period during which such disclosure would be seriously
detrimental (excluding any consideration of market price fluctuation due to the
sale of the Registrable Securities), provided that (except as provided in clause
(iii) above) the Company may not defer the filing for a period of more than
ninety (90) days after receipt of the request of the Initiating Holders, and,
provided further, that



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the Company shall not defer its obligation in this manner more than once in any
twelve-month period.

               (c) UNDERWRITING. The right of any Holder to registration
pursuant to Section 2.1 shall be conditioned upon such Holder's participation in
such underwriting and the inclusion of such Holder's Registrable Securities in
the underwriting (unless otherwise mutually agreed by a majority in interest of
the Initiating Holders and such Holder with respect to such participation and
inclusion) to the extent provided herein. A Holder may elect to include in such
underwriting all or a part of the Registrable Securities he holds.

               (d) PROCEDURES. The Company shall (together with all Holders and
other persons proposing to distribute their securities through such
underwriting) enter into an underwriting agreement in customary form with the
representative of the underwriter or underwriters selected for such underwriting
by a majority in interest of the Initiating Holders, which underwriters are
reasonably acceptable to the Company. Notwithstanding any other provision of
this Section 2.1, if the representative of the underwriters advises the
Initiating Holders in writing that marketing factors require a limitation on the
number of shares to be underwritten, the number of shares to be included in the
underwriting or registration shall be allocated as set forth in Section 2.12
hereof. If a person who has requested inclusion in such registration as provided
above does not agree to the terms of any such underwriting, such person shall be
excluded therefrom by written notice from the Company, the underwriter or the
Initiating Holders. The securities so excluded shall also be withdrawn from
registration. Any Registrable Securities or other securities excluded shall also
be withdrawn from such registration. If shares are so withdrawn from the
registration and if the number of shares to be included in such registration was
previously reduced as a result of marketing factors pursuant to this Section
2.1(d), then the Company shall offer to all Holders who have retained rights to
include securities in the registration the right to include additional
securities in the registration in an aggregate amount equal to the number of
shares so withdrawn, with such shares to be allocated among such Holders
requesting additional inclusion in accordance with Section 2.12.

        2.2 COMPANY REGISTRATION.

               (a) If the Company shall determine to register any of its
securities either for its own account or the account of a security holder or
holders exercising their respective demand registration rights (other than
pursuant to Section 2.1 or 2.4 hereof), other than a registration relating
solely to employee benefit plans, or a registration relating solely to a Rule
145 transaction, or a registration on any registration form that does not permit
secondary sales, the Company will (X) promptly give to each Holder written
notice thereof and (Y) use its best efforts to include in such registration (and
any related qualification under blue sky laws or other compliance), except as
set forth in Section 2.2(b) below, and in any underwriting involved therein, all
the Registrable Securities specified in a written request or requests, made by
any Holder and received by the Company within twenty (20) days after the written
notice from the Company described in clause (i) above is mailed or delivered by
the Company. Such written request may specify all or a part of a Holder's
Registrable Securities.

               (b) UNDERWRITING. If the registration of which the Company gives
notice is for a registered public offering involving an underwriting, the
Company shall so advise the Holders as



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a part of the written notice given pursuant to Section 2.2(a)(i). In such event,
the right of any Holder to registration pursuant to this Section 2.2 shall be
conditioned upon such Holder's participation in such underwriting and the
inclusion of such Holder's Registrable Securities in the underwriting to the
extent provided herein. All Holders proposing to distribute their securities
through such underwriting shall (together with the Company and the other holders
of securities of the Company with registration rights to participate therein
distributing their securities through such underwriting) enter into an
underwriting agreement in customary form with the representative of the
underwriter or underwriters selected by the Company.

        Notwithstanding any other provision of this Section 2.2, if the
representative of the underwriters advises the Company in writing that marketing
factors require a limitation on the number of shares to be underwritten, the
representative may (subject to the limitations set forth below) exclude all
Registrable Securities (other than pursuant to Section 2.1 or 2.4 hereof) from,
or limit the number of Registrable Securities to be included in, the
registration and underwriting. If the registration is the first
Company-initiated registered offering of the Company's securities to the general
public, the Company may limit, to the extent so advised by the underwriters, the
amount of securities (including Registrable Securities) to be included in the
registration by the Company's stockholders (including the Holders), or may
exclude, to the extent so advised by the underwriters, such underwritten
securities entirely from such registration; provided, however, that any such
limitation or cut back shall be first applied to all shares proposed to be sold
in such offering other than for the account of the Company which are not
Registrable Securities. If such registration is the second or any subsequent
Company-initiated registered offering of the Company's securities to the general
public, the Company may limit, to the extent so advised by the underwriters, the
amount of securities to be included in the registration by the Company's
stockholders (including the Holders); provided, however, that any such
limitation or cutback shall first be applied to all shares proposed to be sold
in such offering other than for the account of the Company which are not
Registrable Securities; provided, further, that the aggregate value of
Registrable Securities to be included in such registration by the Holders may
not be so reduced to less than twenty-five percent (25%) of the total value of
all securities included in such registration. The Company shall so advise all
holders of securities requesting registration, and the number of shares of
securities that are entitled to be included in the registration and underwriting
shall be allocated first to the Company for securities being sold for its own
account and thereafter as set forth in Section 2.12. If any person does not
agree to the terms of any such underwriting, he shall be excluded therefrom by
written notice from the Company or the underwriter. Any Registrable Securities
or other securities excluded or withdrawn from such underwriting shall be
withdrawn from such registration.

        If shares are so withdrawn from the registration and if the number of
shares of Registrable Securities to be included in such registration was
previously reduced as a result of marketing factors, the Company shall then
offer to all persons who have retained the right to include securities in the
registration the right to include additional securities in the registration in
an aggregate amount equal to the number of shares so withdrawn, with such shares
to be allocated among the persons requesting additional inclusion in accordance
with Section 2.12 hereof.

        2.3 EXPENSES OF REGISTRATION. All Registration Expenses incurred in
connection with any registration, qualification or compliance pursuant to
Sections 2.2 and 2.4 hereof, and the first



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two registrations pursuant to Section 2.1 hereof and reasonable fees of one
counsel for the Holders in the case of registrations pursuant to Section 2.1
shall be borne by the Company; provided, however, that if the Holders bear the
Registration Expenses for any registration proceeding begun pursuant to Section
2.1 and subsequently withdrawn by the Holders registering shares therein, such
registration proceeding shall not be counted as a requested registration
pursuant to Section 2.1 hereof, except in the event that such withdrawal is
based upon material adverse information relating to the Company that is
different from the information known or available (upon request from the Company
or otherwise) to the Holders requesting registration at the time of their
request for registration under Section 2.1, in which event such registration
shall not be treated as a counted registration for purposes of Section 2.1
hereof, even though the Holders do not bear the Registration Expenses for such
registration. All Selling Expenses relating to securities so registered shall be
borne by the holders of such securities pro rata on the basis of the number of
shares of securities so registered on their behalf.

        2.4 REGISTRATION ON FORM S-3.

               (a) After its initial public offering, the Company shall use its
best efforts to qualify for registration on Form S-3 or any comparable or
successor form or forms. After the Company has qualified for the use of Form
S-3, the Holders of Registrable Securities shall have the right to request
registrations on Form S-3 (such requests shall be in writing and shall state the
number of shares of Registrable Securities to be disposed of and the intended
methods of disposition of such shares by such Holder or Holders), provided,
however, that the Company shall not be obligated to effect any such registration
if (i) the Holders, together with the holders of any other securities of the
Company entitled to inclusion in such registration, propose to sell Registrable
Securities and such other securities (if any) on Form S-3 at an aggregate price
to the public of less than $1,000,000, (ii) in the event that the Company shall
furnish the certification described in Section 2.1(b) (but subject to the
limitations set forth therein), (iii) in a given twelve-month period, after the
Company has effected one (1) such registration in any such period or (iv) it is
to be effected more than five (5) years after the Company's initial public
offering.

               (b) If a request complying with the requirements of Section
2.4(a) hereof is delivered to the Company, the provisions of Sections 2.1(a) and
(b) shall apply to such registration. If the registration is for an underwritten
offering, the provisions of Sections 2.1(c) and (d) shall apply to such
registration.

        2.5 REGISTRATION PROCEDURES. In the case of each registration effected
by the Company pursuant to Section 2, the Company will keep each Holder advised
in writing as to the initiation of each registration and as to the completion
thereof. At its expense, the Company will use its best efforts to:

               (a) Keep (i) a registration on Form S-1 effective for a period of
ninety (90) days or until the Holder or Holders have completed the distribution
described in the registration statement relating thereto, whichever first occurs
and (ii) a registration on Form S-3 effective for a period of 180 days or until
the Holder or Holders have completed the distribution described in the
registration statement related thereto, whichever first occurs (each an
"EFFECTIVENESS PERIOD"); provided, however, that the Effectiveness Period shall
be extended for a period of time equal to the period the Holder refrains from
selling any securities included in such registration at



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the request of the Company or of an underwriter of Common Stock (or other
securities) of the Company.

               (b) Prepare and file with the Commission such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement;

               (c) Furnish such number of prospectuses and other documents
incident thereto, including any amendment of or supplement to the prospectus, as
a Holder from time to time may reasonably request;

               (d) Notify each seller of Registrable Securities covered by such
registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading or incomplete in the light of the
circumstances then existing, and at the request of any such seller, prepare and
furnish to such seller a reasonable number of copies of a supplement to or an
amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such shares, such prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading or
incomplete in the light of the circumstances then existing;

               (e) Cause all such Registrable Securities registered pursuant
hereunder to be listed on each securities exchange on which similar securities
issued by the Company are then listed;

               (f) Provide a transfer agent and registrar for all Registrable
Securities registered pursuant to such registration statement and a CUSIP number
for all such Registrable Securities, in each case not later than the effective
date of such registration;

               (g) Otherwise use its best efforts to comply with all applicable
rules and regulations of the Commission, and make available to its security
holders, as soon as reasonably practicable, an earnings statement covering the
period of at least twelve months, but not more than eighteen months, beginning
with the first month after the effective date of the Registration Statement,
which earnings statement shall satisfy the provisions of Section 11(a) of the
Securities Act; and

               (h) In connection with any underwritten offering pursuant to a
registration statement filed pursuant to Section 2.1 hereof, the Company will
enter into an underwriting agreement reasonably necessary to effect the offer
and sale of Common Stock, provided such underwriting agreement contains
customary underwriting provisions and provided further that if the underwriter
so requests the underwriting agreement will contain customary contribution
provisions.



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        2.6 INDEMNIFICATION.

               (a) The Company will indemnify each Holder, each of its officers,
directors and partners, legal counsel, and accountants and each person
controlling such Holder within the meaning of Section 15 of the Securities Act,
with respect to which registration, qualification, or compliance has been
effected pursuant to this Section 2, and each underwriter, if any, and each
person who controls within the meaning of Section 15 of the Securities Act any
underwriter, against all expenses, claims, losses, damages, and liabilities (or
actions, proceedings, or settlements in respect thereof) arising out of or based
on any untrue statement (or alleged untrue statement) of a material fact
contained in any prospectus, offering circular, or other document (including any
related registration statement, notification, or the like) incident to any such
registration, qualification, or compliance with this Section 2, or based on any
omission (or alleged omission) to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, or
any violation by the Company of the Securities Act or any rule or regulation
thereunder applicable to the Company and relating to action or inaction required
of the Company in connection with any such registration, qualification, or
compliance, and will reimburse each such Holder, each of its officers,
directors, partners, legal counsel, and accountants and each person controlling
such Holder, each such underwriter, and each person who controls any such
underwriter, for any legal and any other expenses reasonably incurred in
connection with investigating and defending or settling any such claim, loss,
damage, liability, or action, provided that the Company will not be liable in
any such case to the extent that any such claim, loss, damage, liability, or
expense arises out of or is based on any untrue statement or omission based upon
written information furnished to the Company by such Holder or underwriter and
stated to be specifically for use therein; unless such information was
subsequently corrected in a writing specifically noting the correction furnished
to the Company prior to the filing of the registration statement. It is agreed
that the indemnity agreement contained in this Section 2.6(a) shall not apply to
amounts paid in settlement of any such loss, claim, damage, liability, or action
if such settlement is effected without the consent of the Company (which consent
has not been unreasonably withheld).

               (b) Each Holder will, if Registrable Securities held by him are
included in the securities as to which such registration, qualification, or
compliance is being effected, indemnify the Company, each of its directors,
officers, partners, legal counsel, and accountants and each underwriter, if any,
of the Company's securities covered by such a registration statement, each
person who controls the Company or such underwriter within the meaning of
Section 15 of the Securities Act, each other such Holder and Other Stockholder,
and each of their officers, directors, and partners, and each person controlling
such Holder or Other Stockholder, against all claims, losses, damages and
liabilities (or actions in respect thereof) arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any such registration statement, prospectus, offering circular, or other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, and will reimburse the Company and such Holders, Other Stockholders,
directors, officers, partners, legal counsel, and accountants, persons,
underwriters, or control persons for any legal or any other expenses reasonably
incurred in connection with investigating or defending any such claim, loss,
damage, liability, or action, in each case to the extent, but only to the
extent, that such untrue statement (or alleged untrue statement) or omission (or
alleged omission) is made in such registration statement, prospectus,



                                       9.
<PAGE>   10
offering circular, or other document in reliance upon and in conformity with
written information furnished to the Company by such Holder and stated to be
specifically for use therein provided, however, that the obligations of such
Holder hereunder shall not apply to amounts paid in settlement of any such
claims, losses, damages, or liabilities (or actions in respect thereof) if such
settlement is effected without the consent of such Holder (which consent shall
not be unreasonably withheld).

               (c) Each party entitled to indemnification under this Section 2.6
(the "INDEMNIFIED PARTY") shall give notice to the party required to provide
indemnification (the "INDEMNIFYING PARTY") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or any litigation resulting
therefrom, shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld), and the Indemnified Party may participate in such
defense at such party's expense, and provided further that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Section 1, to the extent such
failure is not prejudicial. No Indemnifying Party, in the defense of any such
claim or litigation, shall, except with the consent of each Indemnified Party,
consent to entry of any judgment or enter into any settlement that does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such Indemnified Party of a release from all liability in respect to such
claim or litigation. Each Indemnified Party shall furnish such information
regarding itself or the claim in question as an Indemnifying Party may
reasonably request in writing and as shall be reasonably required in connection
with defense of such claim and litigation resulting therefrom.

               (d) If the indemnification provided for in this Section 2.6 is
held by a court of competent jurisdiction to be unavailable to an Indemnified
Party with respect to any loss, liability, claim, damage, or expense referred to
therein, then the Indemnifying Party, in lieu of indemnifying such Indemnified
Party hereunder, shall contribute to the amount paid or payable by such
Indemnified Party as a result of such loss, liability, claim, damage, or expense
in such proportion as is appropriate to reflect the relative fault of the
Indemnifying Party on the one hand and of the Indemnified Party on the other in
connection with the statements or omissions that resulted in such loss,
liability, claim, damage, or expense as well as any other relevant equitable
considerations. The relative fault of the Indemnifying Party and of the
Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission to state a material fact relates to information supplied by the
Indemnifying Party or by the Indemnified Party and the parties' relative intent,
knowledge, access to information, and opportunity to correct or prevent such
statement or omission.

               (e) Notwithstanding the foregoing, to the extent that the
provisions on indemnification and contribution contained in the underwriting
agreement entered into in connection with the underwritten public offering are
in conflict with the foregoing provisions, the provisions in the underwriting
agreement shall control.

        2.7 INFORMATION BY HOLDER. Each Holder of Registrable Securities shall
furnish to the Company such information regarding such Holder and the
distribution proposed by such Holder



                                      10.
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as the Company may reasonably request in writing and as shall be reasonably
required in connection with any registration, qualification, or compliance
referred to in this Section 2.

        2.8 LIMITATIONS ON REGISTRATION OF ISSUES OF SECURITIES. From and after
the date of this Agreement, the Company shall not, without the prior written
consent of a majority in interest of the Holders, enter into any agreement with
any holder or prospective holder of any securities of the Company giving such
holder or prospective holder any registration rights the terms of which are more
favorable than the registration rights granted to the Holders hereunder.

        2.9 RULE 144 REPORTING. With a view to making available the benefits of
certain rules and regulations of the Commission that may permit the sale of the
Restricted Securities to the public without registration, the Company agrees to
use its best efforts to:

               (a) Make and keep public information regarding the Company
available as those terms are understood and defined in Rule 144 under the
Securities Act, at all times from and after ninety (90) days following the
effective date of the first registration under the Securities Act filed by the
Company for an offering of its securities to the general public;

               (b) File with the Commission in a timely manner all reports and
other documents required of the Company under the Securities Act and the
Exchange Act at any time after it has become subject to such reporting
requirements;

               (c) So long as a Holder owns any Restricted Securities, furnish
to the Holder forthwith upon written request a written statement by the Company
as to its compliance with the reporting requirements of Rule 144 (at any time
from and after ninety (90) days following the effective date of the first
registration statement filed by the Company for an offering of its securities to
the general public), and of the Securities Act and the Exchange Act (at any time
after it has become subject to such reporting requirements), a copy of the most
recent annual or quarterly report of the Company, and such other reports and
documents so filed as a Holder may reasonably request in availing itself of any
rule or regulation of the Commission allowing a Holder to sell any such
securities without registration.

        2.10 TRANSFER OR ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause
the Company to register securities granted to a Holder by the Company under this
Section 1 may be transferred or assigned by a Holder only to a transferee or
assignee of not less than 100,000 shares of Registrable Securities (as presently
constituted and subject to subsequent adjustments for stock splits, stock
dividends, reverse stock splits, and the like), provided that the Company is
given written notice at the time of or within a reasonable time after such
transfer or assignment, stating the name and address of the transferee or
assignee and identifying the securities with respect to which such registration
rights are being transferred or assigned, and, provided further, that the
transferee or assignee of such rights assumes the obligations of such Holder
under this Section 2.

        2.11 "MARKET STAND-OFF" AGREEMENT. If requested by the Company and an
underwriter of Common Stock (or other securities) of the Company, an Investor
shall not sell or otherwise transfer or dispose of any Common Stock (or other
securities) of the Company held by such Investor (other than those included in
the registration) during a period of up to one hundred



                                      11.
<PAGE>   12
eighty (180) days following the effective date of a registration statement of
the Company filed under the Securities Act, provided that such agreement shall
only apply to the first such registration statement of the Company, including
securities to be sold on its behalf to the public in an underwritten offering.

        The obligations described in this Section 2.11 shall not apply to a
registration relating solely to employee benefit plans on Form S-1 or Form S-8
or similar forms that may be promulgated in the future, or a registration
relating solely to a Commission Rule 145 transaction on Form S-4 or similar
forms that may be promulgated in the future. The Company may impose
stop-transfer instructions with respect to the shares (or securities) subject to
the foregoing restriction until the end of such one hundred eighty (180) day
period.

        2.12 ALLOCATION OF REGISTRATION OPPORTUNITIES. In any circumstance in
which all of the Registrable Securities and other shares of Common Stock of the
Company (including shares of Common Stock issued or issuable upon conversion of
shares of any currently unissued series of Preferred Stock of the Company) with
registration rights (the "OTHER SHARES") requested to be included in a
registration on behalf of the Holders or other selling stockholders cannot be so
included as a result of limitations of the aggregate number of shares of
Registrable Securities and Other Shares that may be so included, the number of
shares of Registrable Securities and Other Shares that may be so included shall
be allocated among the Holders and other selling stockholders requesting
inclusion of shares pro rata on the basis of the number of shares of Registrable
Securities and Other Shares that would be held by such Holders and other selling
stockholders, assuming conversion; provided, however, so that such allocation
shall not operate to reduce the aggregate number of Registrable Securities and
Other Shares to be included in such registration, if any Holder or other selling
stockholder does not request inclusion of the maximum number of shares of
Registrable Securities and Other Shares allocated to him pursuant to the
above-described procedure, the remaining portion of his allocation shall be
reallocated among those requesting Holders and other selling stockholders whose
allocations did not satisfy their requests pro rata on the basis of the number
of shares of Registrable Securities and Other Shares which would be held by such
Holders and other selling stockholders, assuming conversion, and this procedure
shall be repeated until all of the shares of Registrable Securities and Other
Shares which may be included in the registration on behalf of the Holders and
other selling stockholders have been so allocated. The Company shall not limit
the number of Registrable Securities to be included in a registration pursuant
to this Agreement in order to include shares held by stockholders with no
registration rights existing on the date hereof or to include founder's stock or
any other shares of stock issued to employees, officers, directors, or
consultants pursuant to incentive stock plans of the Company, or, with respect
to registrations under Sections 2.1 or 2.4 hereof, in order to include in such
registration securities registered for the Company's own account.

        2.13 DELAY OF REGISTRATION. No Holder shall have any right to take any
action to restrain, enjoin, or otherwise delay any registration as the result of
any controversy that might arise with respect to the interpretation or
implementation of this Section 2.

        2.14 TERMINATION. This Section 2 shall terminate five years after the
initial public offering of the Company or earlier as to a particular Holder if
such Holder can sell all of the Holder's Registrable Securities in a 90-day
period pursuant to Rule 144.



                                      12.
<PAGE>   13
SECTION 3.

        The Company hereby covenants and agrees, so long as any Holder owns any
Registrable Securities, as follows:

        3.1 BASIC FINANCIAL INFORMATION. The Company will furnish the following
reports to each Holder, which owns at least 200,000 Shares, or such number of
shares of Common Stock issued upon conversion of 200,000 or more Shares, or any
combination thereof (as presently constituted and subject to subsequent
adjustment for stock splits, stock dividends, reverse stock splits,
recapitalizations and the like), and to each Holder which represents that it is
a "venture capital operating company" for purposes of Department of Labor
Regulation Section 2510.3-101 (a "SIGNIFICANT HOLDER"):

               (a) (As soon as practicable after the end of each fiscal year of
the Company, and in any event within ninety (90) days thereafter, a consolidated
balance sheet of the Company and its subsidiaries, if any, as at the end of such
fiscal year, and consolidated statements of income and cash flows of the Company
and its subsidiaries, if any, for such year, prepared in accordance with
generally accepted accounting principles consistently applied and setting forth
in each case in comparative form the figures for the previous fiscal year, all
in reasonable detail and certified by independent public accountants of
recognized national standing selected by the Company, and a Company prepared
comparison to the Company's operating plan for such year.

               (b) As soon as practicable after the end of the first, second,
and third quarterly accounting periods in each fiscal year of the Company, and
in any event within forty-five (45) days thereafter, a consolidated balance
sheet of the Company and its subsidiaries, if any, as of the end of each such
quarterly period, and consolidated statements of income and cash flows of the
Company and its subsidiaries for such period and for the current fiscal year to
date, prepared in accordance with generally accepted accounting principles
consistently applied and setting forth in comparative form the figures for the
corresponding periods of the previous fiscal year and to the Company's operating
plan then in effect and approved by its Board of Directors, subject to changes
resulting from normal year-end audit adjustments, all in reasonable detail and
certified by the principal financial or accounting officer of the Company,
except that such financial statements need not contain the notes required by
generally accepted accounting principles.

               (c) Annually (but in any event at least thirty (30) days prior to
the commencement of each fiscal year of the Company) the financial plan of the
Company, in such manner and form as approved by the Board of Directors of the
Company, which financial plan shall include a projection of income and a
projected cash flow statement for such fiscal year and a projected balance sheet
as of the end of such fiscal year. Any material changes in such business plan
shall be submitted as promptly as practicable after such changes have been
approved by the Board of Directors of the Company.

        3.2 OBSERVER RIGHTS. So long as two (2) million shares of Preferred
Stock remain outstanding, the Company will permit a representative of the
holders of the Preferred Stock (the "OBSERVER") to attend all meetings of the
Company's Board of Directors (the "BOARD") and all committees thereof (whether
in person, telephonic or other) in a non-voting, observer capacity



                                      13.
<PAGE>   14
and shall provide to the Observer, concurrently with the members of the Board,
and in the same manner, notice of such meeting and a copy of all materials
provided to such members; provided, however, that the Observer shall agree to
hold in confidence and trust and to act in a fiduciary manner with respect to
all information so provided; and, provided further, that the Company reserves
the rights to withhold any information and to exclude the Observer from any
meeting or portion thereof if access to such information or attendance at such
meeting could adversely affect the attorney-client privilege between the Company
and its counsel or would result in disclosure of trade secrets to the Observer.

        3.3 VISITATION AND INSPECTION RIGHTS.

               (a) The Company will permit any Holder (or a representative of
any Significant Holder) to visit and inspect any of the properties of the
Company, including its books of account and other records (and make copies
thereof and take extracts therefrom), and to discuss its affairs, finances and
accounts with the Company's officers and its independent public accountants, all
at such reasonable times and as often as any such person may reasonably request.

               (b) The provisions of Section 3.1 and this Section 3.3 shall not
be in limitation of any rights which any Holder or Significant Holder may have
with respect to the books and records of the Company and its subsidiaries, or to
inspect their properties or discuss their affairs, finances and accounts, under
the laws of the jurisdictions in which they are incorporated.

               (c) Anything in Section 3 to the contrary notwithstanding, no
Holder or Significant Holder by reason of this Agreement shall have access to
any trade secrets or classified information of the Company. Each Significant
Holder hereby agrees to hold in confidence and trust and not to misuse or
disclose any confidential information provided pursuant to this Section 2.2. A
Significant Holder may disclose confidential information to employees and
consultants provided that they are bound by confidentiality provisions and use
restrictions at least as restrictive as those imposed on the Significant Holder
pursuant to this Section 3.3(c). The Company shall not be required to comply
with this Section 3.3 in respect of any Holder whom the Company reasonably
determines to be a competitor or an officer, employee, director or greater than
5% stockholder of a competitor.

               (d) As soon as practicable after transmission or occurrence and
in any event within ten days thereof, copies of any reports or communications
delivered to any class of the Company's security holders or broadly to the
financial community.

               (e) Each Holder who represents to the Company that it is a
"venture capital operating company" for purposes of Department of Labor
Regulation Section 2510.3-101 shall in addition have the right to consult with
and advise the officers of the Company as to the management of the Company.

        3.4 RIGHT OF FIRST REFUSAL. The Company hereby grants to each Holder who
owns any Shares or any shares of Common Stock issued upon conversion of the
Shares the right of first refusal to purchase a pro rata share of New Securities
(as defined in this Section 3.4) which the Company may, from time to time,
propose to sell and issue. A Holder's pro rata share, for



                                      14.
<PAGE>   15
purposes of this right of first refusal, is the ratio of the number of shares of
Common Stock owned by such Holder immediately prior to the issuance of New
Securities, assuming full conversion of the Shares and exercise of an option or
warrant held by such Holder, to the total number of shares of Common Stock
outstanding immediately prior to the issuance of New Securities, assuming full
conversion of the Shares and exercise of all outstanding rights, options and
warrants to acquire Common Stock of the Company. Each Holder shall have a right
of over-allotment such that if any Holder fails to exercise its right hereunder
to purchase its pro rata share of New Securities, the other Holders may purchase
the non-purchasing Holder's portion on a pro rata basis within ten (10) days
from the date such non-purchasing Holder fails to exercise its right hereunder
to purchase its pro rata share of New Securities. This right of first refusal
shall be subject to the following provisions:

               (a) "NEW SECURITIES" shall mean any capital stock (including
Common Stock and/or Preferred Stock) of the Company whether now authorized or
not, and rights, options or warrants to purchase such capital stock, and
securities of any type whatsoever that are, or may become, convertible into
capital stock; provided that New Securities does not include (i) securities
purchased under the Series A Agreement, Series B Agreement or Series C
Agreement; (ii) securities issued upon conversion of the Shares; (iii)
securities issued pursuant to the acquisition of another business entity or
business segment of any such entity by the Company by merger, purchase of
substantially all the assets or other reorganization, if such acquisition is
approved by the Board of Directors; (iv) any borrowings, direct or indirect,
from financial institutions or other persons by the Company, whether or not
presently authorized, including any type of loan or payment evidenced by any
type of debt instrument, provided that if such borrowing has any equity features
including warrants, options or other rights to purchase capital stock or is not
convertible into capital stock of the Company, then such borrowing shall have
been approved by the Board of Directors; (v) securities issued to employees,
consultants, officers or directors of the Company pursuant to any stock option,
stock purchase or stock bonus plan, agreement or arrangement approved by the
Board of Directors; (vi) securities issued upon exercise of the warrants
outstanding as of the date hereof; (vii) securities issued in connection with
obtaining lease financing, whether issued to a lessor, guarantor or other
person, if such financing is approved by the Board of Directors; (viii)
securities issued in a public offering pursuant to a registration under the
Securities Act; (ix) securities issued in connection with any stock split, stock
dividend or recapitalization of the Company; and (x) any right, option or
warrant to acquire any security convertible into the securities excluded from
the definition of New Securities pursuant to subsections (i) through (ix) above.

               (b) In the event the Company proposes to undertake an issuance of
New Securities, it shall give each Holder written notice of its intention,
describing the type of New Securities, and their price and the general terms
upon which the Company proposes to issue the same. Each Holder shall have twenty
(20) days after any such notice is mailed or delivered to agree to purchase such
Holder's pro rata share of such New Securities for the price and upon the terms
specified in the notice by giving written notice to the Company and stating
therein the quantity of New Securities to be purchased.

               (c) In the event the Holders fail to exercise fully the right of
first refusal within such twenty (20) day period and after the expiration of the
ten-day period for the exercise of the over-allotment provisions of this Section
3.4, the Company shall have one hundred twenty (120)



                                      15.
<PAGE>   16
days thereafter to sell or enter into an agreement (pursuant to which the sale
of New Securities covered thereby shall be closed, if at all, within one hundred
twenty (120) days from the date of such agreement) to sell the New Securities
respecting which the Holders' right of first refusal option set forth in this
Section 3.4 was not exercised, at a price and upon terms no more favorable to
the purchasers thereof than specified in the Company's notice to Holders
pursuant to Section 3.4(b). In the event the Company has not sold within such
120-day period or entered into an agreement to sell the New Securities in
accordance with the foregoing within one hundred twenty (120) days from the date
of such agreement, the Company shall not thereafter issue or sell any New
Securities, without first again offering such securities to the Holders in the
manner provided in Section 3.4(b) above.

               (d) The right of first refusal set forth in this Section 3.4 may
not be assigned or transferred, except that (i) such right is assignable by each
Holder to any partner, wholly owned subsidiary or parent of, or to any
corporation or entity that is, within the meaning of the Securities Act,
controlling, controlled by or under common control with, any such Holder, and
(ii) such right is assignable between and among any of the Holders.

        3.5 TERMINATION OF RIGHTS. The rights granted under Section 3.1 shall
expire upon the first sale of Common Stock of the Company to the public effected
pursuant to a registration statement filed with, and declared effective by, the
Securities and Exchange Commission (the "Commission") under the Securities Act.
The rights granted under Sections 3.2, 3.3 and 3.4 shall expire upon the first
sale of Common Stock of the Company to the public effected pursuant to a
registration statement filed with, and declared effective by, the Commission
under the Securities Act.

SECTION 4.

        4.1 GOVERNING LAW. This Agreement shall be governed in all respects by
the laws of the State of California, as if entered into by and between
California residents exclusively for performance entirely within California.

        4.2 SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the
parties hereto.

        4.3 ENTIRE AGREEMENT; AMENDMENT; WAIVER. This Agreement (including the
Exhibits hereto) constitutes the full and entire understanding and agreement
between the parties with regard to the subjects hereof and thereof. Neither this
Agreement nor any term hereof may be amended, waived, discharged or terminated,
except by a written instrument signed by the Company and the holders of at least
a majority of the Registrable Securities and any such amendment, waiver,
discharge or termination shall be binding on all the Holders, but in no event
shall the obligation of any Holder hereunder be materially increased, except
upon the written consent of such Holder.

        4.4 WAIVER OF RIGHT OF FIRST REFUSAL. The Company and holders of a
majority of the Registerable Securities, as that term is defined in the Prior
Investors' Rights Agreement, hereby agree, as evidenced by their signatures
hereto, that all rights granted and covenants made under



                                      16.
<PAGE>   17
Section 3.4 of the Prior Investors' Rights Agreement are hereby waived and
released with respect to the sale and issuance by the Company of its Series C
Preferred Stock pursuant to the Series C Agreement.

        4.5 NOTICES, ETC. All notices and other communications required or
permitted hereunder shall be in writing and shall be mailed by United States
first-class mail, postage prepaid, or delivered personally by hand or nationally
recognized courier addressed (a) if to a Holder, as indicated on the list of
Holders attached hereto as Schedule 1, or at such other address as such holder
or permitted assignee shall have furnished to the Company in writing, or (b) if
to the Company, at 270 East Grand Avenue, South San Francisco, California, or at
such other address as the Company shall have furnished to each holder in
writing. All such notices and other written communications shall be effective
(i) if mailed, five (5) days after mailing and (ii) if delivered, upon delivery.

        4.6 DELAYS OR OMISSIONS. No delay or omission to exercise any right,
power or remedy accruing to any Holder, upon any breach or default of the
Company under this Agreement shall impair any such right, power or remedy of
such Holder nor shall it be construed to be a waiver of any such breach or
default, or an acquiescence therein, or of or in any similar breach or default
thereafter occurring; nor shall any waiver of any single breach or default be
deemed a waiver of any other breach or default therefore or thereafter
occurring. Any waiver, permit, consent or approval of any kind or character on
the part of any Holder of any breach or default under this Agreement or any
waiver on the part of any Holder of any provisions or conditions of this
Agreement must be made in writing and shall be effective only to the extent
specifically set forth in such writing. All remedies, either under this
Agreement or by law or otherwise afforded to any Holder, shall be cumulative and
not alternative.

        4.7 RIGHTS; SEPARABILITY. Unless otherwise expressly provided herein, a
Holder's rights hereunder are several rights, not rights jointly held with any
of the other Holders. In case any provision of the Agreement shall be invalid,
illegal or unenforceable, the validity, legality and enforceability of the
remaining provisions shall not in any way be affected or impaired thereby.

        4.8 INFORMATION CONFIDENTIAL. Each Holder acknowledges that the
information received by them pursuant hereto may be confidential and for its use
only, and it will not use such confidential information in violation of the
Exchange Act or reproduce, disclose or disseminate such information to any other
person (other than its employees or agents having a need to know the contents of
such information, and its attorneys), except in connection with the exercise of
rights under this Agreement, unless the Company has made such information
available to the public generally or such Holder is required to disclose such
information by a governmental body.

        4.9 TITLES AND SUBTITLES. The titles of the paragraphs and subparagraphs
of this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

        4.10 ADDITIONAL INVESTORS. Notwithstanding anything to the contrary
contained herein, if the Company shall issue additional shares of its Series C
Preferred Stock pursuant to the Series C Agreement, any purchaser of such shares
of Series C Preferred Stock may become a



                                      17.
<PAGE>   18
party to this Agreement by executing and delivering an additional counterpart
signature page to this Agreement and shall be deemed an "HOLDER" hereunder.

        4.11 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.





                  [Remainder of Page Intentionally Left Blank]


                                      18.
<PAGE>   19
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.


                                       COMPANY:

                                       VIROLOGIC, INC.


                                       By:
                                           -------------------------------------
                                           Martin Goldstein, President




                 [Signature Page to Investor Rights Agreement]
<PAGE>   20
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.

                                       HOLDERS:


                                       BIOTECH GROWTH S.A.



                                       By:
                                          --------------------------------------
                                       Its:  Authorized Signatory


                                       By:
                                          --------------------------------------
                                       Its:  Authorized Signatory




                  [Signature Page to Investor Rights Agreement]

<PAGE>   21
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.


                                       INVESTORS:



                                       -----------------------------------------
                                       AEOW 96, LLC
                                       By: Will K. Weinstein Revoc Trst
                                           Dtd 2/27/90
                                       Its: Member Manager
                                            By:  Will K. Weinstein
                                            Its: Trustee




                 [Signature Page to Investor Rights Agreement]

<PAGE>   22
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.


                                       INVEMED ASSOCIATES LLC


                                       By:
                                          --------------------------------------
                                       Name:  Cristina H. Kepner

                                       Title:
                                             -----------------------------------


                                       -----------------------------------------
                                       CRISTINA H. KEPNER



                  [Signature Page to Investor Rights Agreement]
<PAGE>   23
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.



                                       -----------------------------------------
                                       Richard Beleson




                  [Signature Page to Investor Rights Agreement]
<PAGE>   24
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.


                                       CAPITAL MANAGEMENT SERVICES, INC.


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


                                       -----------------------------------------
                                       STANLEY DRUCKENMILLER


                                       -----------------------------------------
                                       ARMINIO FRAGA


                                       -----------------------------------------
                                       GARY GLADSTEIN


                                       -----------------------------------------
                                       ELIZABETH LARSON


                                       -----------------------------------------
                                       PAUL McNULTY


                                       -----------------------------------------
                                       GABRIEL NECHAMKIN



                                       -----------------------------------------
                                       FILIBERTO VERTICELLI


                                       -----------------------------------------
                                       SEAN WARREN


                                       -----------------------------------------
                                       JOHN ZWAANSTRA


                  [Signature Page to Investor Rights Agreement]
<PAGE>   25
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.


                                       ZESIGER CAPITAL GROUP LLC,
                                       Attorney-In-Fact for each Investor
                                       set forth below


                                       By:
                                          --------------------------------------
                                          Lisa Hess,
                                          Principal


                                          City of Milford Pension and
                                            Retirement Plan
                                          Norwalk Employee Pension Plan
                                          City of Stamford Firemen's
                                            Pension Plan
                                          State of Oregon PERS/ZCG
                                          Dean Witter Foundation
                                          Roanoke College
                                          HBL Charitable Unitrust
                                          Jeanne Morency
                                          Murray Capital, LLC
                                          Morgan Trust Co. of the Bahamas Ltd.
                                              as Trustee U/A/D 11/30/93
                                          William B. Lazar
                                          Wells Family LLC
                                          Harold and Grace Willens JTWROS
                                          Barrie Ramsay Zesiger
                                          Wolfson Investment Partners LP
                                          Alza Corporation Retirement Plan
                                          Tab Products Co. Pension Plan
                                          Planned Parenthood Of NY
                                          Van Loben Sels Charitable Foundation
                                          Public Employee Retirement System Of
                                            Idaho
                                          Albert L. Zesiger


                  [Signature Page to Investor Rights Agreement]
<PAGE>   26
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.


                                       AURORA VENTURES LLC


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


                  [Signature Page to Investor Rights Agreement]
<PAGE>   27
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.





                                       THE RAISER MARITAL TRUST


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


                  [Signature Page to Investor Rights Agreement]
<PAGE>   28
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.



                                       NOTKIN LIVING TRUST, DTD 4/8/92


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


                  [Signature Page to Investor Rights Agreement]
<PAGE>   29
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.



                                       -----------------------------------------
                                       LEWIS C. PELL


                  [Signature Page to Investor Rights Agreement]
<PAGE>   30
        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.



                                       -----------------------------------------
                                       GEORGE SOROS

                                       -----------------------------------------
                                       MARK PEARSON


                                       -----------------------------------------
                                       ROBERT D. BROWNELL

                  [Signature Page to Investor Rights Agreement]
<PAGE>   31
                                   SCHEDULE 1

                                 LIST OF HOLDERS


The Aurora Funds, Inc.
2 Davis Drive
Research Triangle Park, NC 27709
Attn:  Mr. Scott Albert

Capital Management Services, Inc.
11100 Santa Monica Blvd., 15th Floor
Los Angeles, CA 90025

Invemed Associates, Inc.
375 Park Avenue
Suite 2205
New York, NY 10152

Cristina H. Kepner
c/o Invemed Associates, Inc.
375 Park Avenue
Suite 2205
New York, NY 10152

Notkin Living Trust
Capital Guardian Trust & Co.
Four Embarcadero Center
Suite 1800
San Francisco, CA 94111
Attn:  Shelby Notkin

Stanley Druckenmiller
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Arminio Fraga
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Gary Gladstein
c/o Soros Fund Management
888 7th Avenue,



                                       1.
<PAGE>   32
Suite 3300
New York, NY 10106

Elizabeth Larson
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Paul McNulty
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Gabriel Nechamkin
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Filiberto Verticelli
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

Sean Warren
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

John Zwaanstra
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

George Soros
c/o Soros Fund Management
888 7th Avenue,
Suite 3300
New York, NY 10106

WS Investments
c/o Wilson Sonsini Goodrich & Rosati
650 Page Mill Road



                                       2.
<PAGE>   33
Palo Alto, CA 94304

Robert D. Brownell
c/o Wilson Sonsini Goodrich & Rosati
650 Page Mill Road
Palo Alto, CA 94304

Alza Corporation Retirement Plan
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Arthur D. Little Employee Investment Plan
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

City of Milford Pension & Retirement Plan
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Norwalk Employee Pension Plan
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

City of Stamford Firemen's Pension Fund
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

State of Oregon PERS/ZCG
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Roanoke College
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Tab Products Co. Pension Plan
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Planned Parenthood of NY



                                       3.

<PAGE>   34
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Dean Witter Foundation
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Van Loben Sels Charitable Foundation
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

William B. Lazar
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Jeanne Morency
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

HBL Charitable Unitrust
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Morgan Trust Co. of the Bahamas Ltd.
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Wells Family LLC
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Harold & Grace Willens JTWROS
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Murray Capital
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022



                                       4.
<PAGE>   35
Barrie Ramsay Zesiger
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Wolfson Investment Partners
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

The Raiser Marital Trust
c/o Alex Brown Capital Advisory & Trust Co.
19 South Street
Attn: Venedia Andrews
Baltimore, MD  21202

Public Employee Retirement System of Idaho
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022

Albert L. Zesiger
c/o Zesiger Capital Group LLC
320 Park Avenue
New York, NY 10022


BioTech Growth S.A.
Swiss Bank Tower
Panama 1
Republic of Panama

Asset Management BAB N.V.
6 Plasa Smeets
Curacao
Netherlands Antilles

Mark Pearson
Catalyst Real Estate Group
2483 Bayshore Rd,
Suite 102
Palo Alto, CA  94303

Louis Pell
11 Carpentedr Way
Armonk   NY  10504



                                       5.
<PAGE>   36
AEOW 96, LLC
909 Montgomery, Suite 600
San Francisco, CA  94133
Attn:  Will K. Weinstein



                                       6.