Document:

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                                                                     EXHIBIT 4.2

                                  STENTOR, INC.

                              AMENDED AND RESTATED

                           INVESTORS' RIGHTS AGREEMENT

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                                TABLE OF CONTENTS

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1.    Covenants of the Company ........................................................         1

      1.1     Information Rights ......................................................         1
      1.2     Reservation of Common Stock .............................................         3
      1.3     Stock Vesting ...........................................................         3
      1.4     Key Person Insurance ....................................................         3
      1.5     Proprietary Information and Inventions Agreement ........................         3
      1.6     Approval ................................................................         3
      1.7     Directors' Liability and Indemnification ................................         3
      1.8     Certain Covenants Relating to Management and Board Participation ........         4

2.    Registration Rights .............................................................         4

      2.1     Certain Definitions .....................................................         4
      2.2     Demand Registration .....................................................         6
      2.3     Piggyback Registration ..................................................         7
      2.4     Registration on Form S-3 ................................................         8
      2.5     Expenses of Registration ................................................         9
      2.6     Registration Procedures ........................ ........................         9
      2.7     Delay of Registration ...................................................        11
      2.8     Indemnification .........................................................        11
      2.9     Information by Holder ...................................................        12
      2.10    Rule 144 Reporting ......................................................        13
      2.11    Transfer of Registration Rights .........................................        13
      2.12    Standoff Agreement ......................................................        13
      2.13    Termination of Registration Rights ......................................        14

3.    Preemptive Rights ...............................................................        14

      3.1     General .................................................................        14
      3.2     Right of First Refusal ..................................................        14
      3.3     Expiration of Right of First Refusal ....................................        15

4.    Voting Agreement ........ .......................................................        15

      4.1     Shares Subject to Agreement .............................................        15
      4.2     Voting of Board of Directors ............................................        15
      4.3     Successors in Interest ..................................................        16

5.    Termination of Rights ...........................................................        16

      5.1     Transfer to Competitors .................................................        16

6.    Miscellaneous ...................................................................        16

      6.1     Additional Investors ....................................................        16
      6.2     Waivers and Amendments ..................................................        16
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                                TABLE OF CONTENTS
                                   (CONTINUED)

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6.3   Notices .........................................................................        17
6.4   Descriptive Headings ............................................................        17
6.5   Governing Law ...................................................................        17
6.6   Counterparts ....................................................................        17
6.7   Expenses ........................................................................        17
6.8   Successors and Assigns ..........................................................        17
6.9   Entire Agreement ................................................................        17
6.10  Separability Severability .......................................................        17
6.11  Stock Splits ....................................................................        18
6.12  Aggregation of Stock. ...........................................................        18
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                                  STENTOR, INC.

                AMENDED AND RESTATED INVESTORS' RIGHTS AGREEMENT

      THIS AGREEMENT is made as of August 11, 2000 among Stentor, Inc., a
Delaware corporation (the "Company"), the holders of the Company's Series A
Preferred Stock listed on Exhibit A attached hereto (collectively, the "Series A
Holders"), the holders of the Company's Series B Preferred Stock listed on
Exhibit A attached hereto (collectively, the "Series B Holders"), the holders of
the Company's Common Stock listed on Exhibit A attached hereto (collectively,
the "Common Holders") and the purchasers of the Company's Series C Preferred
Stock ("Preferred Stock") listed on Exhibit B hereto (each an "Investor," and
collectively, the "Investors").

                                    RECITALS

      WHEREAS, the Investors desire to obtain certain (i) rights regarding
registration of the Company's securities under the Securities Act of 1933, as
amended ("Registration Rights"), and (ii) preemptive rights regarding the
Company's equity offerings ("Preemptive Rights"), and (iii) rights to
information ("Information Rights").

      WHEREAS, the Company, to induce the Investors to invest, desires to grant
the Investors such rights.

      WHEREAS, the Series A Holders, the Series B Holders, the Common Holders
and the Company are parties to the Investors' Rights Agreement dated April 2,
1999 (the "Original Agreement").

      WHEREAS, in accordance with Section 5.2 of the Original Agreement, the
holders of sixty-six and two thirds percent (66 2/3%) of the outstanding shares
of Series A Preferred and Series B Preferred voting as separate series have
consented to the Amendment and Restatement of the Original Agreement.

      WHEREAS, the execution of this Agreement is a condition to the closing of
the transactions contemplated by the Series C Preferred Stock Purchase Agreement
which shall be executed by and between the Series C Holders and the Company on
the date hereof.

      WHEREAS, the Shareholders and the Company desire that the transactions
contemplated by the Series C Purchase Agreement be consummated.

      NOW, THEREFORE, the parties agree as follows:

      1. Covenants of the Company.

            1.1 Information Rights.

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                  (a) Annual Financial Statements. The Company will provide to
each Investor as soon as practicable after the end of each fiscal year, and in
any event within 90 days thereafter, a consolidated balance sheet of the Company
and its subsidiaries, if any, as of the end of such fiscal year, and
consolidated statements of income, stockholders' equity and cash flows of the
Company and its subsidiaries, if any, for such year, prepared in accordance with
generally accepted accounting principles ("GAAP") and setting forth in each case
in comparative form the figures for the previous fiscal year, all in reasonable
detail and which shall be audited by a public accounting firm as may be
determined by the Board of Directors. Such annual financial statements shall be
certified by either the President, Chief Executive Officer or Chief Financial
Officer of the Company.

                  (b) Monthly Financial Statements. So long as an Investor is a
licensed Small Business Investment Company ("SBIC") or an Investor (and its
affiliates) holds at least 100,000 shares of the Company's Preferred Stock (or
Common Stock, options thereupon, or a combination thereof) or ten percent (10%)
of the Company's outstanding stock (on an as-converted basis), the Company shall
provide such Investor as soon as practicable after the end of each month and in
any event within 30 days thereafter, a consolidated balance sheet of the Company
and its subsidiaries, if any, as of the end of each such month, consolidated
statements of income, and a consolidated statement of cash flow of the Company
and its subsidiaries for such period and for the current fiscal year to date,
and setting forth in each case in comparative form the figures for corresponding
periods in the previous fiscal year, prepared in accordance with GAAP
consistently applied with prior practice for earlier periods (with the exception
of footnotes that may be required by GAAP and provided that the foregoing shall
not restrict the right of the Company to change its accounting principles
consistent with GAAP, if the Board of Directors determines that it is in the
best interest of the Company to do so), all in reasonable detail.

                  (c) Annual Budget and Business Plan. So long as an Investor is
a SBIC or an Investor (and its affiliates) holds at least 100,000 shares of the
Company's Preferred Stock (or Common Stock, options thereupon or a combination
thereof) or ten percent (10%) of the Company's outstanding stock (on an
as-converted basis), the Company shall provide, as soon as practicable, but in
any event thirty (30) days prior to the end of each fiscal year, an operating
plan for the next fiscal year.

                  (d) Additional Information. So long as an Investor is a SBIC
or an Investor (and its affiliates) holds at least 100,000 shares of the
Company's Preferred Stock (or Common Stock, options thereupon or a combination
thereof) or ten percent (10%) of the Company's outstanding stock (on an
as-converted basis), the Company will allow such Investor to visit and inspect
any of the properties of the Company (upon reasonable advance notice) and will
deliver or provide to such Investor with reasonable promptness, (i) copies of
all notices, minutes, consents and the like provided to the Board of Directors
of the Company, and (ii) such other information and data, including access to
books, records, officers and accountants, with respect to the Company and its
subsidiaries as any such Investor may from time to time reasonably request;
provided, however, that the Company shall not be obligated to provide any
information that it considers in good faith to be a trade secret or to contain
confidential or classified information unless the recipient first executes a
Nondisclosure Agreement in a form reasonably acceptable to the Company.

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                  (e) Termination of Covenants. The rights set forth in Section
1.1 shall terminate and be of no further force or effect upon the closing of a
firmly underwritten public offering of the Company's securities to the public
pursuant to an effective registration statement filed by the Company in
accordance with the provisions of this Agreement under the Securities Act of
1933, as amended at an aggregate offering price of not less than $20,000,000
(after deduction of underwriter commissions and offering expenses) which price
shall be based on a valuation of the Company of not less than $200 million
("Qualified Public Offering"), or on the date the Company otherwise becomes
subject to the reporting requirements under Section 13 or 15(d) of the
Securities Exchange Act, as amended, whichever first occurs.

            1.2 Reservation of Common Stock. The Company will at all times
reserve and keep available, solely for issuance and delivery upon the conversion
of the Preferred Stock, all Common Stock issuable from time to time upon such
conversion.

            1.3 Stock Vesting. Unless otherwise approved by the Board of
Directors, all stock options and other stock equivalents issued after the date
of .this Agreement to employees, directors, consultants and other service
providers shall be subject to vesting as follows: (i) twenty-five percent (25%)
of such stock shall vest at the end of the first year following the earlier of
the date of issuance or such person's services commencement date with the
Company, and (ii) seventy-five percent (75%) of such stock shall vest monthly in
equal installments over the remaining thirty-six (36) months. With respect to
any shares of stock purchased by any such person, the Company's repurchase
option shall provide that upon such person's termination of employment or
service with the Company, with or without cause, the Company or its assignee (to
the extent permissible under applicable securities laws and other laws) shall
have the option to purchase at cost any unvested shares of stock held by such
person.

            1.4 Key Person Insurance. Subject to the approval of the Board of
Directors, the Company will use its best efforts to obtain and maintain in full
force and effect term life insurance in the amount of one million ($1,000,000)
dollars on the Company's Chief Executive Officer; naming the Company as
beneficiary.

            1.5 Proprietary Information and Inventions Agreement. The Company
shall require all employees and consultants to execute and deliver a Proprietary
Information and Inventions Agreement in a form approved by the Company's Board
of Directors.

            1.6 Approval. The Company shall not without the unanimous consent of
the Board of Directors, authorize or enter into any material transactions
outside of the ordinary course of business with any director or management
employee, or such director's or employee's immediate family.

            1.7 Directors' Liability and Indemnification. The Company's
Certificate of Incorporation and Bylaws shall provide (i) for elimination of the
liability of each director of the Company to the maximum extent permitted by law
and (ii) for indemnification of directors for acts on behalf of the Company to
the maximum extent permitted by law. In addition, the Company shall enter into
and use its best efforts to at all times maintain indemnification contracts in a
form to be

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approved by counsel for the directors, with each of its directors to indemnify
such directors to the maximum extent permissible under Delaware law. If
determined advisable by the Board of Directors, the Company shall have in force
a directors and officers liability insurance policy in an amount and with a
carrier approved by the unanimous consent of the Board of Directors.

            1.8 Certain Covenants Relating to Management and Board
Participation.

                  (a) Consultation with Management. The Investors shall be
entitled to consult with and advise management of the Company on significant
business issues, including management's proposed annual operating plans, and
management will meet with Investors regularly during each year at the Company's
facilities at mutually agreeable times for such consultation and advise and to
review progress in achieving said plans.

                  (b) Inspection of Books and Records. The Investors may examine
the books and records of the Company and inspect its facilities and may request
information at reasonable times and intervals concerning the general status of
the Company's financial condition and operations, provided that access to highly
confidential proprietary information and facilities need not be provided unless
the recipient first executes a Nondisclosure Agreement in form reasonably
acceptable to the Company.

                  (c) Board of Directors Representative. If, at any time, either
of the Sanderling or Caduceus venture capital firms or UPMC Health System
("UPMCHS") control Investors holding an aggregate of at least 250,000 shares of
outstanding stock of the Company and there is not a representative of
Sanderling, Caduceus or UPMCHS on the Company's Board of Directors, the Company
shall invite Sanderling, Caduceus and/or UPMCHS (whichever is not already on the
Board of Directors) to attend all meetings of its Board of Directors in a
non-voting observer capacity, and in this respect shall give such representative
copies of all notices, minutes, consents and other material that it provides to
its directors; provided, however, that the Company reserves the right to exclude
such representative from access to any material or meeting or portion thereof if
the Company believes upon advice of counsel that such exclusion is reasonably
necessary (i) to preserve the attorney-client privilege or to protect against a
conflict of interest with such individual, (ii) because such portion of the
meeting is an executive session limited solely to Board members and legal
counsel, or (iii) to protect highly confidential proprietary information or for
other similar reasons unless the recipient first executes a Nondisclosure
Agreement in form reasonably acceptable to the Company. Such representative may
participate in discussions of matters brought to the Board of Directors.

      2. Registration Rights.

            2.1 Certain Definitions. As used in this Agreement, the following
terms shall have the following respective meanings:

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

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                  (b) "Holder" shall mean the Investors holding Registrable
Securities or securities convertible or exercisable into Registrable Securities
and any person holding such securities to whom the rights under this Section 2
have been transferred in accordance with Section 2.11 hereof.

                  (c) "Initiating Holders" shall mean any Holder or Holders who
in the aggregate hold at least 50% of the Registrable Securities.

                  (d) "Participating Holders" shall mean any Holder or Holders
who propose to distribute their securities through a registration pursuant to
this Section 2.

                  (e) "Registrable Securities" means the Common Stock issued or
issuable upon conversion of Preferred Stock issued by the Company pursuant to a
Preferred Stock Purchase Agreement and any Common Stock of the Company issued or
issuable in respect of the Preferred Stock, Common Stock issued to the
University of Pittsburgh-Of the Commonwealth System of Higher Education (the
"University") pursuant to a Stock Issuance Agreement dated December 21, 1998 or
issuable to the University in respect of an option to purchase shares of the
Company's Common Stock dated December 21, 1998 or other securities issuable
pursuant to the conversion of the Preferred Stock or upon any stock split, stock
dividend, recapitalization, or similar event; provided however that shares of
Common Stock or other securities shall only be treated as Registrable Securities
for purposes of Section 2.3 hereof (A) if and so long as they have not been sold
to or through a broker or dealer or underwriter in a public distribution or a
public securities transaction, or (B) prior to the date such securities have
been sold or are all available for immediate sale in the opinion of counsel to
the Company in a transaction exempt from the prospectus delivery requirements of
the Securities Act so that all transfer restrictions and legends with respect
thereto are removed upon the consummation of such sale.

                  (f) The terms "register," "registered" and "registration"
refer to a registration effected by preparing and filing a registration
statement in compliance with the Securities Act, and the declaration or ordering
of the effectiveness of such registration statement.

                  (g) "Registration Expenses" shall mean all expenses incurred
by the Company in complying with Sections 2.2, 2.3 and 2.4 hereof (but excluding
underwriting discounts and commissions), including the reasonable expenses of
one (1) special counsel selected by a majority in interest of the Participating
Holders.

                  (h) "Restricted Securities" shall mean the securities of the
Company required to bear a legend indicating that transfer is restricted in the
absence of registration.

                  (i) "Securities Act" shall mean the Securities Act of 1933, as
amended, or any similar federal statute and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.

                  (j) "Selling Expenses" shall mean all underwriting discounts,
selling commissions and stock transfer taxes, if any, applicable to the
securities registered by the Holders.

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            2.2 Demand Registration.

                  (a) Request for Registration. In case the Company shall
receive from Initiating Holders a written request that the Company effect any
registration, qualification or compliance with respect to at least fifty percent
(50%) of the Registrable Securities or Registrable Securities with an expected
aggregate offering price to the public of at least $20,000,000, net of
underwriting discounts and commissions, which price shall be based on a
valuation of the Company of not less than $200 million the Company will (1)
within ten days of the receipt by the Company of such notice, give written
notice of the proposed registration, qualification or compliance to all other
Holders and (2) as soon as practicable (but within 120 days after receipt of the
request of the Initiating Holders), use its commercially reasonable best efforts
to effect such registration, qualification or compliance (including, without
limitation, appropriate qualification under applicable blue sky or other state
securities laws and appropriate compliance with applicable regulations issued
under the Securities Act and any other governmental requirements or regulations)
as may be so requested 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 20 days after receipt of such
written notice from the Company; provided, however, that the Company shall not
be obligated to take any action to effect any such registration, qualification
or compliance pursuant to this Section 2.2(a):

                        (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) Prior to the earlier of August 10, 2003 or twelve
months after the effective date of the Company's first Qualified Public Offering
of its securities;

                        (iii) During the period starting with the date sixty
(60) days prior to the Company's good faith estimate of the date of filing of,
and ending on the date six (6) months immediately following the effective date
of, any registration statement pertaining to securities of the Company (other
than a registration of securities in a Rule 145 transaction, with respect to an
employee benefit plan or with respect to the Company's first Qualified Public
Offering of its securities), provided that the Company is actively employing in
good faith all reasonable efforts to cause such registration statement to become
effective;

                        (iv) After the Company has effected a registration
pursuant to this Section 2.2(a), which registration has been declared or ordered
effective;

                        (v) If 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 it would be detrimental to the Company
or its shareholders for a registration statement to be filed in the near future,
then the Company's obligation to use its best efforts to register, qualify or
comply under this Section 2.2 shall be deferred for a period not to exceed 90
days from the date of

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receipt of written request from the Initiating Holders; provided, however, that
the Company shall not exercise such right more than twice in any twelve-month
period.

                  (b) Underwriting. In the event that a registration pursuant to
this Section 2.2 is for a registered public offering involving an underwriting,
the Company shall so advise the Holders as part of the notice given pursuant to
Section 2.2(a). 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 the
underwriting arrangements required by this Section 2.2, and the inclusion of
such Holder's Registrable Securities in the underwriting to the extent requested
shall be limited to the extent provided herein.

            The Company shall, together with all Participating Holders, enter
into an underwriting agreement in customary form with the managing underwriter
selected for such underwriting by the Company and reasonably acceptable to a
majority of the Participating Holders. Notwithstanding any other provision of
this Section 2.2, if the managing underwriter advises the Company in writing
that marketing factors require a limitation of the number of shares to be
underwritten, then the Company shall so advise all Holders of Registrable
Securities and the number of shares of Registrable Securities that may be
included in the registration and underwriting shall be allocated among all
Holders thereof in proportion, as nearly as practicable, to the respective
amounts of Registrable Securities held by such Holders at the time of filing the
registration statement or in such other manner as shall be agreed to by the
Company and Holders of a majority of the Registrable Securities proposed to be
included in such registration; provided, however, that the number of shares of
Registrable Securities to be included in such underwriting shall not be reduced
unless all other securities are first entirely excluded from the underwriting.
No Registrable Securities excluded from the underwriting by reason of the
underwriter's marketing limitation shall be included in such registration. To
facilitate the allocation of shares in accordance with the above provisions, the
Company or the underwriters may round the number of shares allocated to any
Holder to the nearest 100 shares.

            If any Holder of Registrable Securities disapproves of the terms of
the underwriting, such Holder may elect to withdraw therefrom by written notice
to the Company, the managing underwriter and the Initiating Holders. The
Registrable Securities and/or other securities so withdrawn shall also be
withdrawn from registration, and such Registrable Securities shall not be
transferred in a public distribution prior to 90 days after the effective date
of such registration, or such other shorter period of time as the underwriters
may require.

            2.3 Piggyback Registration.

                  (a) Notice of Registration. If at any time or from time to
time the Company shall determine to register any of its securities, either for
its own account or the account of a security holder or holders, other than a
registration relating solely to employee benefit plans, a registration relating
solely to a Commission Rule 145 transaction, or a registration pursuant to
Section 2.2 hereof, the Company will (i) promptly give to each Holder written
notice thereof, and (ii) include in such registration (and any related
qualification under blue sky laws or other compliance),

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and in any underwriting involved therein, all the Registrable Securities
specified in a written request or requests, made within 15 days after receipt of
such written notice from the Company, by any Holder.

                  (b) Underwriting. If the registration of which the Company
gives notice is for a Qualified Public Offering involving an underwriting, the
Company shall so advise the Holders as a part of the written notice given
pursuant to 2.3(a). In such event the right of any Holder to registration
pursuant to 2.3 shall be conditioned upon such Holder's participation in such
underwriting and the inclusion of 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) enter into an
underwriting agreement in customary form with the managing underwriter selected
for such underwriting by the Company. Notwithstanding any other provision of
this Section 2.3, if the managing underwriter or Company determines that
marketing factors require a limitation of the number of shares to be
underwritten, the managing underwriter may limit or completely exclude the
Registrable Securities and other securities to be distributed through such
underwriting, provided that, subsequent to the Company's initial Qualified
Public Offering, the Registrable Securities to be included in such registration
may not be limited to less than 30% of the total number of securities to be
included in such registration. The Company shall so advise all Holders
distributing their securities through such underwriting of such limitation (or
exclusion, if applicable) and the number of shares of Registrable Securities
that may be included in the registration and underwriting shall be allocated (if
applicable) among all such Holders in proportion, as nearly as practicable, to
the respective amounts of Registrable Securities held by such Holders at the
time of filing the registration statement. To facilitate the allocation of
shares in accordance with the above provisions, the Company may round the number
of shares allocated to any Holder or holder to the nearest 100 shares.

            If any Participating Holder disapproves of the terms of any such
underwriting, such Participating Holder may elect to withdraw therefrom by
written notice to the Company and the managing underwriter. Any securities
excluded or withdrawn from such underwriting shall be withdrawn from such
registration, and shall not be transferred in a public distribution prior to 90
days after the effective date of the registration statement relating thereto, or
such other shorter period of time as the underwriters may require. If shares are
withdrawn from registration, the Company shall offer to all persons retaining
the right to include securities in the registration the right to include
additional securities in the registration, with such shares being allocated
among all such Participating Holders in proportion, as nearly as practicable, to
the respective amounts of Registrable Securities held by such Participating
Holders at the time of filing the registration statement.

                  (c) Right to Terminate Registration. The Company shall have
the right to terminate or withdraw any registration initiated by it under this
Section 2.3 prior to the effectiveness of such registration whether or not any
Holder has elected to include securities in such registration. The Registration
Expenses of such withdrawn registration shall be borne by the Company in
accordance with Section 2.5 hereof.

            2.4 Registration on Form S-3.

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                  (a) Request for Registration. Following the Company's initial
public offering, the Company shall use its best efforts to become eligible to
register offerings of securities on SEC Form S-3 or its successor form. After
the Company has qualified for the use of Form S-3, Holders of Registrable
Securities then outstanding shall have the right to request registration on Form
S-3 (which request shall be in writing and shall state the number of shares of
Registrable Securities to be registered and the intended method of disposition
of shares by such Holders); provided that no more than two such registrations
must be effected during any twelve month period. The Company shall not be
obligated to take any action to effect any such registration, qualification or
compliance pursuant to this Section 2.4(a)

                        (i) unless the Holders requesting registration propose
to dispose of Registrable Securities having an anticipated aggregate price to
the public (before deduction of underwriting discounts and expenses of sale) of
at least $1,000,000;

                        (ii) during the period starting with the date sixty (60)
days prior to the Company's estimated date of filing of, and ending on the date
six (6) months immediately following the effective date of, any registration
statement pertaining to securities of the Company (other than a registration of
securities in a Rule 145 transaction or with respect to an employee benefit
plan), provided that the Company is actively employing in good faith all
reasonable efforts to cause such registration statement to become effective;

                        (iii) more than twice in any twelve month period;

                        (iv) if the Company shall furnish to such Holder a
certificate signed by the President of the Company stating that in the good
faith judgment of the Board of Directors it would be detrimental to the Company
or its shareholders for registration statements to be filed in the near future,
then the Company's obligation to use its best efforts to file a registration
statement shall be deferred for a period not to exceed 90 days from the receipt
of the request to file such registration by such Holder or Holders; provided,
however, that the Company shall not exercise such right more than twice in any
twelve-month period; or

                        (v) after the Company has effected three registrations
pursuant to this Section 2.4, which registrations have been declared or ordered
effective.

            2.5 Expenses of Registration. All Registration Expenses incurred in
connection with registrations pursuant to Sections 2.2, 2.3 and 2.4 shall be
borne by the Company (including the reasonable expenses of one special counsel
of the Participating Holders to be selected by a majority in interest of the
Participating Holders). All other Selling Expenses relating to securities
registered on behalf of the Holders shall be borne by the holders of securities
included in such registration pro rata with the Company and among each other on
the basis of the number of shares so registered.

            2.6 Registration Procedures. In the case of each registration,
qualification or compliance effected by the Company pursuant to this Section 2,
the Company will keep each Holder advised in writing as to the initiation of
each registration, qualification and compliance and as to the completion
thereof. At its expense the Company will:

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                  (a) Prepare and file with the Commission a registration
statement with respect to such securities and use its best efforts to cause such
registration statement to become and remain effective until the distribution
described in the Registration Statement has been completed (up to a maximum of
120 days);

                  (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 to the Participating Holders and to the
underwriters of the securities being registered such reasonable number of copies
of the registration statement, preliminary prospectus, final prospectus and such
other documents as such underwriters may reasonably request in order to
facilitate the public offering of such securities.

                  (d) Use its commercially reasonable best efforts to register
and qualify the securities covered by such registration statement under such
other securities or blue sky laws of such jurisdictions as shall be reasonably
requested by the Participating Holders, provided that the Company shall not be
required in connection therewith or as a condition thereto to qualify to do
business or to file a general consent to service of process in any such states
or jurisdictions, unless the Company is already subject to service in such
jurisdiction and except as may be required by the Securities Act.

                  (e) In the event of any underwritten public offering, enter
into and perform its obligations under an underwriting agreement, in usual and
customary form, with the managing underwriter of such offering. Each Holder
shall also enter into and perform its obligations under such an agreement.

                  (f) Notify each Participating Holder at any time when a
prospectus relating thereto is required to be delivered under the Securities Act
or upon 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 in the light
of the circumstances then existing.

                  (g) Cause all securities covered by such registration
statement to be listed on each securities exchange or authorized for quotation
on each automated quotation system on which similar securities issued by the
Company are then listed or authorized for quotation.

                  (h) Provide a transfer agent and registrar for all securities
covered by such registration statement and a CUSIP number for all such
Registrable Securities, in each case not later than the effective date of such
registration.

                  (i) Furnish, at the request of any Participating Holder, on
the date that the securities are delivered to the underwriters for sale in
connection with a registration being sold

                                      -10-
<PAGE>

through underwriters, (i) an opinion, dated such date, of the counsel
representing the Company for the purposes of such registration, in form and
substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, if any, and to the Participating
Holders and (ii) a letter dated such date, from the independent certified public
accountants of the Company, in form and substance as is customarily given by
independent certified public accountants to underwriters in an underwritten
public offering, addressed to the underwriters, if any, and to the Holders
requesting registration of Registrable Securities.

            2.7 Delay of Registration. No Holder shall have any right to obtain
or seek an injunction restraining or otherwise delaying any such registration as
the result of any controversy that might arise with respect to the
interpretation or implementation of this Section 2.

            2.8 Indemnification. In the event any Registrable Securities are
included in a registration statement under this Section 2:

                  (a) To the extent permitted by law, the Company will indemnify
each Participating Holder, each of its officers, directors, partners and legal
counsel, and each person controlling such Participating 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 3, and
each underwriter, if any, and each person who controls any underwriter within
the meaning of Section 15 of the Securities Act, against all expenses, claims,
losses, damages or liabilities (or actions in respect thereof), including any of
the foregoing incurred in settlement of any litigation, commenced or threatened,
arising out of or based on any untrue statement (or alleged untrue statement) of
a material fact contained in any registration statement, prospectus, offering
circular or other document, or any amendment or supplement thereto, incident to
any such registration, qualification or compliance, 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, in light of the circumstances in
which they were made, not misleading, or any violation by the Company of the
Securities Act or any rule or regulation promulgated under the Securities Act
applicable to the Company in connection with any such registration,
qualification or compliance, and the Company will pay to each such Participating
Holder, each of its officers, directors, partners, and legal counsel and each
person controlling such Participating Holder, each such underwriter and each
person who controls any such underwriter, as incurred, any legal and any other
expenses reasonably incurred in connection with investigating, preparing or
defending 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 or alleged untrue statement or omission, made in reliance
upon and in conformity with written information furnished to the Company by an
instrument duly executed by such Participating Holder, controlling person or
underwriter and stated to be specifically for use therein.

                  (b) To the extent permitted by law, each Participating Holder
will, if Registrable Securities held by such Participating Holder are included
in the securities as to which such registration, qualification or compliance is
being effected, indemnify the Company, each of its directors, officers, and
legal counsel, each underwriter, if any, of the Company's securities covered

                                      -11-
<PAGE>

by such a registration statement, each person who controls the Company or such
underwriter within the meaning of Section 15 of the Securities Act, and each
other Participating Holder, each of its officers, directors, partners and legal
counsel and each person controlling such Participating Holder within the meaning
of Section 15 of the Securities Act, 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 pay the Company, such Participating Holders, such
directors, officers, persons, underwriters or control persons, as incurred 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, offering circular or other document in reliance upon and
in conformity with written information furnished to the Company by an instrument
duly executed by such Holder and stated to be specifically for use therein.
Notwithstanding the foregoing, the liability of each Holder under this
subsection (b) shall be limited in an amount equal to the proceeds to each such
Holder of Registrable Securities sold as contemplated herein, unless such
liability resulted from willful misconduct by such Holder. A Holder will not be
required to enter into any agreement or undertaking in connection with any
registration under this Section 2 providing for any indemnification or
contribution on the part of such Holder greater than the Holder's obligations
under this Section 2.8(b).

                  (c) Each party entitled to indemnification under this Section
2.8 (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 any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, 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 2 unless the failure to give such notice is
materially prejudicial to an Indemnifying Party's ability to defend such action
and provided further, that the Indemnifying Party shall not assume the defense
for matters as to which there is a conflict of interest or separate and
different defenses but shall bear the expense of such defense nevertheless. 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 which 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.

            2.9 Information by Holder. It shall be a condition precedent to the
obligations of the Company to take any action pursuant to this Section 2 with
respect to the Registrable Securities of any selling Holder that such holder
shall furnish to the Company such information regarding

                                      -12-
<PAGE>

itself, the Registrable Securities held by it, and the intended method of
disposition of such securities as shall be required to effect the registration
of such Holder's Registrable Securities.

            2.10 Rule 144 Reporting. With a view to making available the
benefits of certain rules and regulations of the Commission which may at any
time permit the sale of the Restricted Securities to the public without
registration, after such time as a public market exists for the Common Stock of
the Company, the Company agrees to use its commercially reasonable best efforts
to:

                  (a) Make and keep public information available, as those terms
are defined in Rule 144 under the Securities Act, at all times after the
effective date that the Company becomes subject to the reporting requirements of
the Securities Act or the Securities Exchange Act of 1934, as amended (the
"Exchange Act").

                  (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 an Investor owns any Restricted Securities,
upon request, (i) a written statement by the Company as to its compliance with
the reporting requirements of said Rule 144 (at any time after 90 days after 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), (ii) a copy of the most recent annual or quarterly report of the
Company and (iii) such other reports and documents of the Company and other
information in the possession of or reasonably obtainable by the Company as an
Investor may reasonably request in availing itself of any rule or regulation of
the Commission allowing an Investor to sell any such securities without
registration.

            2.11 Transfer of Registration Rights. Except as otherwise provided
in Section 4, the rights to cause the Company to register securities granted
Holders under Sections 2.2, 2.3 and 2.4 may be assigned (i) to a transferee or
assignee in connection with any transfer or assignment of Registrable Securities
by a Holder of not less than 100,000 shares of Registrable Securities, or (ii)
to any transferee or assignee who is a constituent partner of a Holder or the
estate of such constituent partner, or to any transferee or assignee who is a
family member of the Holder or a trust for the benefit of the Holder or any
family member of the Holder, provided that, with respect to each such transfer
or assignment, the Company be give a prior written notice of the transfer, the
transferee or assignee agree in writing to all provisions contained in this
Section 2 and that such transfer otherwise be effected in accordance with
applicable securities laws.

            2.12 Standoff Agreement. Each Holder agrees in connection with the
Company's initial Qualified Public Offering of the Company's securities, upon
request of the Company or the underwriters managing any underwritten offering of
the Company's securities, not to sell, make any short sale of, loan, grant any
option for the purchase of, or otherwise dispose of any Registrable Securities
(other than those included in the registration) without the prior written
consent of the Company or such underwriters, as the case may be, for such period
of time (not to exceed one

                                      -13-
<PAGE>

hundred eighty (180) days) from the effective date of such registration as may
be requested by the underwriters, provided that the Company shall use its best
efforts to obtain similar agreements from each of the Company's officers,
directors and holders of one percent (1%) or more of the Company's stock (on an
as-converted basis).

            2.13 Termination of Registration Rights. The rights granted under
this Section 2 shall terminate on the first to occur of (i) the fifth
anniversary of the consummation of the initial Qualified Public Offering of the
Company's securities, (ii) as to any Holder, at such time as such Holder owns
Securities consistently less than 1% of the outstanding voting stock of the
Company and such Holder is able to offer for sale all of its Registrable
Securities within a given three-month period pursuant to Rule 144 of the
Securities Act.

      3. Preemptive Rights.

            3.1 General. Except for (i) conversion rights applicable to the
Company's Preferred Stock, (ii) securities issued pursuant to a Qualified Public
Offering, (iii) securities issued pursuant to the Company's acquisition of
another corporation by merger, purchase of substantially all the assets or other
corporate reorganization, (iv) securities issued in connection with any stock
split or stock dividend of the Company, recapitalizations or the like, (v)
securities issued after the date hereof to employees, officers, or directors of,
or contractors, consultants or advisors to, the Company pursuant to stock
purchase or stock option plans, stock bonuses or awards, contracts or other
arrangements that are approved by the Company's Board of Directors or (vi)
securities issued to independent non-Shareholder third parties in connection
with equipment lease financing transactions approved by the Company's Board of
Directors, the Company will not, nor will it permit any subsidiary to, authorize
or issue any shares of stock of the Company of any class and will not authorize,
issue or grant any options, warrants, conversion rights or other rights to
purchase or acquire any shares of stock of the Company of any class without
offering the Investors the right of first refusal described below.

            3.2 Right of First Refusal. Each Investor which holds at least 2,000
shares of Preferred and/or Common Stock of the Company shall have a right of
first refusal to purchase an amount of securities of the Company of any class or
kind which the Company proposes to sell in a nonregistered private placement
(other than the issuance of shares contemplated by Section 3.1 above)
("Preemptive Securities") sufficient to maintain such Investor's proportionate
beneficial ownership interest in the Company (on an as-converted, fully diluted
basis). If the Company wishes to make any such sale of Preemptive Securities, it
shall give the Investors written notice of the proposed sale. The notice shall
set forth (i) the Company's bona fide intention to offer Preemptive Securities
and (ii) the material terms and conditions of the proposed sale (including the
number of shares to be offered and the price, if any, for which the Company
proposes to offer such shares), and shall constitute an offer to sell Preemptive
Securities to the Investors on such terms and conditions. Any Investor may
accept such offer by delivering a written notice of acceptance (an "Acceptance
Notice") to the Company within thirty (30) days after receipt of the Company's
notice of the proposed sale. Any Investor exercising its right of first refusal
shall be entitled to participate in the purchase of Preemptive Securities on a
pro rata basis to the extent necessary to maintain such

                                      -14-
<PAGE>

Investor's proportionate beneficial ownership interest in the Company (such
Investor's "Pro Rata Portion") (for purposes of determining such Investor's Pro
Rata Portion, any Investor or other security holder shall be treated as owning
that number of shares of Common Stock into which any outstanding convertible
securities may be converted and for which any outstanding options may be
exercised). The Company shall, in writing, inform each Investor which elects to
purchase its Pro Rata Portion of Preemptive Securities of any other Investor's
failure to do so, in which case the Investors electing to purchase such shares
of Preemptive Securities shall have the right to purchase all of such shares on
a pro rata basis. If any Investor who elects to exercise its right of first
refusal does not complete the purchase of such Preemptive Securities within
thirty (30) days after delivery of its Acceptance Notice to the Company, the
Company may complete the sale of Preemptive Securities on the terms and
conditions specified in the Company's notice within the ninety (90) day period
following the expiration of such thirty (30) day period. If the Company does not
enter into an agreement for the sale of such shares within such thirty (30) day
period, or if such agreement is not consummated within such ninety (90) day
period, the right provided hereunder shall be deemed to be revived and all
future shares of Preemptive Securities shall not be offered unless first
reoffered to the Investors in accordance with this Section 3. An Investor shall
be entitled to apportion the right of first refusal hereby granted among itself
and its partners and affiliates in such proportions it deems appropriate.

            3.3 Expiration of Right of First Refusal. The right of first refusal
granted under this Agreement shall expire when the Company consummates a
Qualified Public Offering.

      4. Voting Agreement.

            4.1 Shares Subject to Agreement. Each Investor hereby agrees to hold
all of its shares of Common Stock, Preferred Stock and Common Stock issuable
upon conversion of Preferred Stock held or acquired in the future (collectively,
the "Voting Shares") subject to, and to vote the Voting Shares in accordance
with, the provisions of this Agreement.

            4.2 Voting of Board of Directors. The Investors hereby agree to vote
the Voting Shares as to which they have beneficial ownership to elect to the
Board of Directors:

                  (i) two nominees by the holders of Common Stock;

                  (ii) one nominee by the holders of Series A Preferred (for as
long they hold at least five percent (5%) of the outstanding common stock of the
Company on an as converted basis);

                  (iii) one nominee by the holders of Series B Preferred (for as
long they hold at least five percent (5%) of the outstanding common stock of the
Company on an as converted basis), which person shall be nominated by the
Sanderling entities; and

                  (iv) one nominee by the holders of Series C Preferred (for as
long they hold at least five percent (5%) of the outstanding common stock of the
Company on an as converted basis), which person shall be nominated by Gilo
Ventures.

                                      -15-
<PAGE>

      An additional independent director shall be appointed by the unanimous
vote of the Board of Directors. In the event that any director elected pursuant
to the terms hereof ceases to serve as a member of the Board, the Company and
the Investors agree to take all such action as is reasonable and necessary,
including the voting of Voting Shares by the Investors as to which they have
beneficial ownership, to cause the election or appointment of such other
substitute person to the Board as may be designated on the terms as provided
herein. Directors will be elected annually and will serve until their successors
are elected or the next annual meeting of shareholders or until their earlier
removal or resignation.

            4.3 Successors in Interest. The provisions of this Section 4 shall
be binding upon all transferees or assignees of the Voting Shares. The Company
shall not permit the transfer of any of the Voting Shares on its books or issue
a new certificate representing any of the Voting Shares unless and until the
person to whom such security is to be transferred shall have executed a written
agreement, substantially in the form of this Agreement, pursuant to which such
person becomes a party to this Agreement and agrees to be bound by all the
provisions hereof as if such person were an Investor on the date hereof.

      5. Termination of Rights.

            5.1 Transfer to Competitors. Upon the transfer of any shares of the
Company's Preferred Stock to a Competitor of the Company (as defined below) the
Information Rights, the Registration Rights and the Preemptive Rights set forth
in this Investors' Rights Agreement shall immediately terminate as to the
transferred shares and be of no further force or effect. A Competitor of the
Company shall be as determined by resolution of the Board of Directors in its
sole and absolute discretion.

      6. Miscellaneous.

            6.1 Additional Investors. Such number of Additional Investors may be
added to this Agreement as may be required to purchase an additional 768,820
shares of Series C Preferred Stock of the Company. Such Investors may become
party to this Agreement, upon execution and delivery to the Company of signature
pages hereto.

            6.2 Waivers and Amendments. With the written consent of the record
or beneficial holders of sixty-six and two thirds percent (66 2/3%) of (i) the
outstanding shares of Series A Preferred, (ii) the Series B Preferred, and (iii)
the Series C Preferred, each voting as a separate series, the rights and
obligations of the Company and the holders of Registrable Securities under this
Agreement may be waived (either generally or in a particular instance, either
retroactively or prospectively, and either for a specified period of time or
indefinitely). With the same consent, the Company, when authorized by resolution
of its Board of Directors, may enter into a supplementary agreement for the
purpose of adding any provisions to or changing in any manner or eliminating any
of the provisions of this Agreement; provided, however, that no such consent
shall be required for the purpose of adding to this Agreement an Investor
pursuant to Section 6.1, or an equipment lessor. No modification, amendment or
waiver shall reduce the sixty-six and two-thirds percentage (66 2/3%) required
pursuant to this Section 6.2 without the consent of all of the

                                      -16-
<PAGE>

Purchasers of the Registrable Securities. If the holders of any class or series
of stock will be adversely affected by any modification, amendment or waiver in
a manner different from the holders of any other class or series of stock, such
adversely affected holders shall be required to approve the modification,
amendment or waiver by a sixty-six and two-thirds percent (66 2/3%) vote of that
class or series, as appropriate. Upon the effectuation of each such waiver,
consent, agreement of amendment or modification, the Company shall promptly give
written notice thereof to the record holders of the Registrable Securities who
have not previously consented thereto in writing. This Agreement or any
provision hereof may be changed, waived, discharged or terminated only by a
statement in writing signed by the party against which enforcement of the
change, waiver, discharge or termination is sought, except to the extent
provided in this Section 6.2 (Waivers and Amendments).

            6.3 Notices. All notices and other communications required or
permitted hereunder shall be in writing and, except as otherwise noted herein,
shall be deemed effectively given upon personal delivery, delivery by nationally
recognized courier or forty-eight (48) hours after being deposited with the
United States Post Office, (by registered mail, postage prepaid) addressed: (a)
if to the Company, at 385 Oyster Point Boulevard, Suite 8B, South San Francisco,
CA 94080 (or at such other address as the Company shall have furnished to the
Holders in writing) and (b) if to a Holder, at the latest address of such person
shown on the Company's records.

            6.4 Descriptive Headings. The descriptive headings herein have been
inserted for convenience only and shall not be deemed to limit or otherwise
affect the construction of any provisions hereof.

            6.5 Governing Law. This Agreement shall be governed by and
Interpreted under the laws of the State of Delaware.

            6.6 Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall for all purposes be deemed to be an original
and all of which shall constitute the same instrument, but only one of which
need be produced.

            6.7 Expenses. If any action at law or in equity is necessary to
enforce or interpret the terms of this Agreement, the prevailing party shall be
entitled to reasonable attorney's fees, costs and necessary disbursements in
addition to any other relief to which such party may be entitled.

            6.8 Successors and Assigns. Except as otherwise expressly provided
in this Agreement, this Agreement shall benefit and bind the successors,
assigns, heirs, executors and administrators of the parties to this Agreement.

            6.9 Entire Agreement. This Agreement constitutes the full and entire
understanding and agreement between the parties with regard to the subject
matter of this Agreement.

            6.10 Separability; Severability. Unless expressly provided in this
Agreement, the rights of each Investor under this Agreement are several rights,
not rights jointly held with any other

                                      -17-
<PAGE>

Investors. Any invalidity, illegality or limitation on the enforceability of
this Agreement with respect to any Investor shall not affect the validity,
legality or enforceability of this Agreement with respect to the other
Investors. If any provision of this Agreement is judicially determined to be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not be affected or impaired.

            6.11 Stock Splits. All references to numbers of shares in this
Agreement shall be appropriately adjusted to reflect any stock dividend, split,
combination or other recapitalization of shares by the Company occurring after
the date of this Agreement.

            6.12 Aggregation of Stock. All shares of Preferred Stock held or
acquired by affiliated entities or persons shall be aggregated together for the
purpose of determining the availability of any rights under this Agreement.

                      [This space intentionally left blank]

                                      -18-
<PAGE>

      IN WITNESS WHEREOF, the parties have executed this Investors' Rights
Agreement on the day and year first set forth above.

THE COMPANY:                           STENTOR,INC.

                                       By: /s/ Oran Muduroglu
                                           ------------------
                                           Oran Muduroglu
                                           Chief Executive Officer and President

          [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

EXISTING HOLDERS

UNIVERSITY OF PITTSBURGH -
OF THE COMMONWEALTH SYSTEM OF
HIGHER EDUCATION

/s/ Amy K. Marsh
------------------------
Amy K. Marsh
Treasurer

/s/ Oran Muduroglu
------------------------
Oran Muduroglu

/s/ John Huffman
------------------------
John Huffman

/s/ Paul Chang
------------------------
Paul Chang

CADUCEUS CAPITAL HEALTH VENTURES, L.P.
BY: CADUCEUS CAPITAL HEALTH VENTURES GP, L.L.C.

/s/ William Golden
------------------------
William Golden
Managing Director

          [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]
<PAGE>

SANDERLING VENTURE PARTNERS IV, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
----------------------------------    ---------------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING IV LIMITED, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
----------------------------------    ---------------------------------------
Fred A. Middleton,                    Robert G. McNeil
General Partner                       General Partner

SANDERLING IV BIOMEDICAL, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
----------------------------------    ---------------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING [FERI TRUST] VENTURE PARTNERS IV, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
----------------------------------    ---------------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

         [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

SANDERLING IV VENTURE MANAGEMENT

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
----------------------------------    ---------------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

/s/ Mark Maletz
----------------------------------
Mark Maletz

THE INVESTORS:

GILO VENTURES

/s/ Stephen Pezzola
----------------------------------
By: Stephen Pezzola
Title: Member

 UPMC HEALTH SYSTEM

/s/ Karen L Hartley
----------------------------------
By: KAREN L HARTLEY
Title: NICE PRESIDENT OF FINANCE
       ASSISTANT TREASURER

CADUCEUS CAPITAL HEALTH VENTURES, L.P.
BY:CADUCEUS CAPITAL HEALTH VENTURES GP, L.L.C.

/s/ William Golden
----------------------------------
William Golden
Managing Director

         [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

SANDERLING VENTURE PARTNERS IV, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
-----------------------------------   --------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING IV LIMITED, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
-----------------------------------   --------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING IV BIOMEDICAL, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
-----------------------------------   --------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING [FERI TRUST] VENTURE PARTNERS IV, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
-----------------------------------   --------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

SANDERLING IV VENTURE MANAGEMENT

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
-----------------------------------   --------------------------------
Fred A. Middleton                     Robert G. McNeil
General Partner                       General Partner

----------------------------------
Mark Maletz

          [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

UNIVERSITY OF PITTSBURGH -
OF THE COMMONWEALTH SYSTEM OF
HIGHER EDUCATION

/s/ Amy K. Marsh
----------------------------------
Amy K. Marsh
Treasurer

          [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

SANDERLING VENTURE PARTNERSHIP IV
CO-INVESTMENT FUND, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
---------------------------------     ----------------------------------
Name: Fred A. Middleton               Name: Robert G. McNeil
Title: General Partner                Title: General Partner

SANDERLING IV BIOMEDICAL
CO-INVESTMENT FUND, L.P.

/s/ Fred A. Middleton                 /s/ Robert G. McNeil
---------------------------------     ----------------------------------
Name: Fred A. Middleton               Name: Robert G. McNeil
Title: General Partner                Title: General Partner

          [SIGNATURE PAGE TO STENTOR, INC. INVESTORS' RIGHTS AGREEMENT]

<PAGE>

EMC INVESTMENT CORPORATION

/s/ Michael Cody
--------------------------------------------
By: Michael Cody
Title: Vice President, Corporate Development
<PAGE>

                                    EXHIBIT A

                         SCHEDULE OF EXISTING INVESTORS

SERIES A HOLDERS

Caduceus Capital Health Ventures, L.P.

SERIES B HOLDERS

Caduceus Capital Health Ventures, L.P.

Sanderling Venture Partners IV, L.P.

Sanderling IV Limited Partnership, L.P.

Sanderling IV Biomedical, L.P.

Sanderling [Feri Trust] Venture Partners IV, G.P.

Sanderling IV Venture Management

Mark Maletz

COMMON HOLDERS

Oran Muduroglu

Paul Chang

John Huffman

University of Pittsburgh

<PAGE>

                                    EXHIBIT B

                             SCHEDULE OF INVESTORS

Gilo Ventures

UPMC Health System

Caduceus Capital Health Ventures, L.P.

Sanderling Venture Partners IV, L.P.

Sanderling IV Limited Partnership, L.P.

Sanderling IV Biomedical, L.P.

Sanderling [Feri Trust] Venture Partners IV, G.P.

Sanderling IV Venture Management

Sanderling Venture Partners IV Co-Investment Fund, L.P.

Sanderling IV Biomedical Co-Investment Fund, L.P.

Mark Maletz

University of Pittsburgh

<PAGE>

                                    EXHIBIT B

                      SCHEDULE OF INVESTORS - SECOND CLOSE

Caduceus Capital Health Ventures, L.P

EMC Investment Corporation<PAGE>

                                                                     Exhibit 4.3

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED OR ANY APPLICABLE STATE SECURITIES LAW,
AND MAY NOT BE SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE
REGISTRATION THEREOF UNDER SUCH ACT OR PURSUANT TO RULE 144 AND AN EXEMPTION
UNDER APPLICABLE STATE LAW OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO
THE CORPORATION AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.

                            WARRANT TO PURCHASE STOCK

Corporation: STENTOR, INC., a Delaware corporation
Number of Shares: 14,243
Class of Stock: Series C Preferred
Initial Exercise Price: $6.67 per share
Issue Date: January 10, 2001
Expiration Date: January 10, 2008

      THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for
other good and valuable consideration, SILICON VALLEY BANK ("Holder") is
entitled to purchase the number of fully paid and nonassessable shares of the
class of securities (the "Shares") of the corporation (the "Company") at the
initial exercise price per Share (the "Warrant Price") all as set forth above
and as adjusted pursuant to Article 2 of this Warrant, subject to the provisions
and upon the terms and conditions set forth in this Warrant.

ARTICLE 1. EXERCISE.

            1.1 Method of Exercise. Holder may exercise this Warrant by
delivering a duly executed Notice of Exercise in substantially the form attached
as Appendix 1 to the principal office of the Company. Unless Holder is
exercising the conversion right set forth in Section 1.2, Holder shall also
deliver to the Company a check for the aggregate Warrant Price for the Shares
being purchased.

            1.2 Conversion Right. In lieu of exercising this Warrant as
specified in Section 1.1, Holder may from time to time convert this Warrant, in
whole or in part, into a number of Shares determined by dividing (a) the
aggregate fair market value of the Shares or other securities otherwise issuable
upon exercise of this Warrant minus the aggregate Warrant Price of such Shares
by (b) the fair market value of one Share. The fair market value of the Shares
shall be determined pursuant to Section 1.3.

            1.3 Fair Market Value. If the Shares are traded in a public market,
the fair market value of the Shares shall be the closing price of the Shares (or
the closing price of the Company's stock into which the Shares are convertible)
reported for the business day immediately before Holder delivers its Notice of
Exercise to the Company. If the Shares are not traded in a public market, the
Board of Directors of the Company shall determine fair market value in its
reasonable good faith judgment.

            1.4 Delivery of Certificate and New Warrant. Promptly after Holder
exercises or converts this Warrant, the Company shall deliver to Holder
certificates for the Shares acquired and, if this Warrant has not been fully
exercised or converted and has not expired, a new Warrant representing the
Shares not so acquired.

            1.5 Replacement of Warrants. On receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and, in the case of loss, theft or destruction, on delivery of an
indemnity agreement reasonably satisfactory in form and amount to the Company
or, in the case of mutilation, or surrender and cancellation of this Warrant,
the Company shall execute and deliver, in lieu of this Warrant, a new warrant of
like tenor.

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            1.6 Assumption on Sale, Merger, or Consolidation of the Company.

                  1.6.1 "Acquisition". For the purpose of this Warrant,
"Acquisition" means any sale, license, or other disposition of all or
substantially all of the assets of the Company, or any reorganization,
consolidation, or merger of the Company where the holders of the Company's
securities before the transaction beneficially own less than 50% of the
outstanding voting securities of the surviving entity after the transaction.

                  1.6.2 Assumption of Warrant. Upon the closing of any
Acquisition, the successor entity shall assume the obligations of this Warrant,
and this Warrant shall be exercisable for the same securities, cash, and
property as would be payable for the Shares issuable upon exercise of the
unexercised portion of this Warrant as if such Shares were outstanding on the
record date for the Acquisition and subsequent closing. The Initial Exercise
Price and/or number of Shares shall be adjusted accordingly.

ARTICLE 2. ADJUSTMENTS TO THE SHARES.

            2.1 Stock Dividends, Splits, Etc. If the Company declares or pays a
dividend on its common stock (or the Shares if the Shares are securities other
than common stock) payable in common stock, or other securities, subdivides the
outstanding common stock into a greater amount of common stock, or, if the
Shares are securities other than common stock, subdivides the Shares in a
transaction that increases the amount of common stock into which the Shares are
convertible, then upon exercise of this Warrant, for each Share acquired, Holder
shall receive, without cost to Holder, the total number and kind of securities
to which Holder would have been entitled had Holder owned the Shares of record
as of the date the dividend or subdivision occurred. If the outstanding shares
are combined or consolidated, by reclassification or otherwise, into a lesser
number of shares, the Initial Exercise Price shall be proportionately increased.

            2.2 Reclassification, Exchange, Combinations or Substitution. Upon
any reclassification, exchange, substitution, or other event that results in a
change of the number and/or class of the securities issuable upon exercise or
conversion of this Warrant, Holder shall be entitled to receive, upon exercise
or conversion of this Warrant, the number and kind of securities and property
that Holder would have received for the Shares if this Warrant had been
exercised immediately before such reclassification, exchange, substitution, or
other event. Such an event shall include any automatic conversion of the
outstanding or issuable securities of the Company of the same class or series as
the Shares to common stock pursuant to the terms of the Company's Articles of
Incorporation upon the closing of a registered public offering of the Company's
common stock. The Company or its successor shall promptly issue to Holder a new
Warrant for such new securities or other property. The new Warrant shall provide
for adjustments which shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Article 2 including, without limitation,
adjustments to the Initial Exercise Price and to the number of securities or
property issuable upon exercise of the new Warrant. The provisions of this
Section 2.2 shall similarly apply to successive reclassifications, exchanges,
substitutions, or other events.

            2.3 Adjustments for Diluting Issuances. The Warrant Price and the
number of Shares issuable upon exercise of this Warrant or, if the Shares are
Preferred Stock, the number of shares of common stock issuable upon conversion
of the Shares, shall be subject to adjustment, from time to time in the manner
set forth in the Company's Articles (Certificate) of Incorporation. The
provisions set forth for the Shares in the Company's Articles (Certificate) of
Incorporation relating to the above in effect as of the Issue Date may not be
amended, modified or waived, without the prior written consent of Holder unless
such amendment, modification or waiver affects Holder in the same manner as they
affect all other shareholders of the same series of shares granted to the
Holder.

            2.4 No Impairment. The Company shall not, by amendment of its
Articles of Incorporation or through a reorganization, transfer of assets,
consolidation, merger, dissolution, issue, or

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sale of securities or any other voluntary action, avoid or seek to avoid the
observance or performance of any of the terms to be observed or performed under
this Warrant by the Company, but shall at all times in good faith assist in
carrying out of all the provisions of this Article 2 and in taking all such
action as may be necessary or appropriate to protect Holder's rights under this
Article against impairment.

            2.5 Fractional Shares. No fractional Shares shall be issuable upon
exercise or conversion of the Warrant and the number of Shares to be issued
shall be rounded down to the nearest whole Share. If a fractional share interest
arises upon any exercise or conversion of the Warrant, the Company shall
eliminate such fractional share interest by paying Holder the amount computed by
multiplying the fractional interest by the fair market value of a full Share.

            2.6 Certificate as to Adjustments. Upon each adjustment of the
Warrant Price, the Company shall promptly notify Holder in writing, and, at the
Company's expense, promptly compute such adjustment, and furnish Holder with a
certificate of its Chief Financial Officer setting forth such adjustment and the
facts upon which such adjustment is based. The Company shall, upon written
request, furnish Holder a certificate setting forth the Warrant Price in effect
upon the date thereof and the series of adjustments leading to such Warrant
Price.

ARTICLE 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

            3.1 Representations and Warranties. The Company represents and
warrants to the Holder as follows:

                  (a) The initial Warrant Price referenced on the first page of
this Warrant is not greater than (i) the price per share at which the Shares
were last issued in an arms-length transaction in which at least $500,000 of the
Shares were sold and (ii) the fair market value of the Shares as of the date of
this Warrant.

                  (b) All Shares which may be issued upon the exercise of the
purchase right represented by this Warrant, and all securities, if any, issuable
upon conversion of the Shares, shall, upon issuance, be duly authorized, validly
issued, fully paid and nonassessable, and free of any liens and encumbrances
except for restrictions on transfer provided for herein or under applicable
federal and state securities laws.

                  (c) The Capitalization Table previously provided to Holder
remains true and complete as of the Issue Date.

            3.2 Notice of Certain Events. If the Company proposes at any time
(a) to declare any dividend or distribution upon its common stock, whether in
cash, property, stock, or other securities and whether or not a regular cash
dividend; (b) to offer for subscription pro rata to the holders of any class or
series of its stock any additional shares of stock of any class or series or
other rights; (c) to effect any reclassification or recapitalization of common
stock; (d) to merge or consolidate with or into any other corporation, or sell,
lease, license, or convey all or substantially all of its assets, or to
liquidate, dissolve or wind up; or (e) offer holders of registration rights the
opportunity to participate in an underwritten public offering of the company's
securities for cash, then, in connection with each such event, the Company shall
give Holder (1) at least 10 days prior written notice of the date on which a
record will be taken for such dividend, distribution, or subscription rights
(and specifying the date on which the holders of common stock will be entitled
thereto) or for determining rights to vote, if any, in respect of the matters
referred to in (c) and (d) above; (2) in the case of the matters referred to in
(c) and (d) above at least 10 days prior written notice of the date when the
same will take place (and specifying the date on which the holders of common
stock will be entitled to exchange their common stock for securities or other
property deliverable upon the occurrence of such event); and (3) in the case of
the matter referred to in (e) above, the same notice as is given to the holders
of such registration rights.

            3.3 Registration Under Securities Act of 1933, as amended. The
Company agrees that the Shares or, if the Shares are convertible into common
stock of the Company, such common stock,

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shall be subject to the registration rights set forth in the Company's Investor
Rights Agreement or similar agreement. The provisions set forth in the Company's
Investors' Right Agreement or similar agreement relating to the above in effect
as of the Issue Date may not be amended, modified or waived without the prior
written consent of Holder unless such amendment, modification or waiver affects
Holder in the same manner as they affect all other shareholders of the same
series of shares granted to the Holder.

ARTICLE 4. REPRESENTATIONS, WARRANTIES OF THE HOLDER. The Holder represents and
warrants to the Company as follows:

            4.1 Purchase for Own Account. Except for transfers to Holder's
affiliates, this Warrant and the securities to be acquired upon exercise of this
Warrant by the Holder will be acquired for investment for the Holder's account,
not as a nominee or agent, and not with a view to the public resale or
distribution within the meaning of the 1933 Act, and the Holder has no present
intention of selling, granting any participation in, or otherwise distributing
the same. If not an individual, the Holder also represents that the Holder has
not been formed for the specific purpose of acquiring this Warrant or the
Shares.

            4.2 Disclosure of Information. The Holder has received or has had
full access to all the information it considers necessary or appropriate to make
an informed investment decision with respect to the acquisition of this Warrant
and its underlying securities. The Holder further has had an opportunity to ask
questions and receive answers from the Company regarding the terms and
conditions of the offering of this Warrant and its underlying securities and to
obtain additional information (to the extent the Company possessed such
information or could acquire it without unreasonable effort or expense)
necessary to verify any information furnished to the Holder or to which the
Holder has access.

            4.3 Investment Experience. The Holder understands that the purchase
of this Warrant and its underlying securities involves substantial risk. The
Holder: (i) has experience as an investor in securities of companies in the
development stage and acknowledges that the Holder is able to fend for itself,
can bear the economic risk of such Holder's investment in this Warrant and its
underlying securities and has such knowledge and experience in financial or
business matters that the Holder is capable of evaluating the merits and risks
of its investment in this Warrant and its underlying securities and/or (ii) has
a preexisting personal or business relationship with the Company and certain of
its officers, directors or controlling persons of a nature and duration that
enables the Holder to be aware of the character, business acumen and financial
circumstances of such persons.

            4.4 Accredited Investor Status. The Holder is an "accredited
investor" within the meaning of Regulation D promulgated under the 1933 Act.

ARTICLE 5. MISCELLANEOUS.

            5.1 Term: This Warrant is exercisable in whole or in part at any
time and from time to time on or before the Expiration Date.

            5.2 Legends. This Warrant and the Shares (and the securities
issuable, directly or indirectly, upon conversion of the Shares, if any) shall
be imprinted with a legend in substantially the following form:

            THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
            1933, AS AMENDED OR UNDER ANY APPLICABLE STATE LAWS, AND MAY NOT BE
            SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE
            REGISTRATION THERE OF UNDER SUCH ACT AND AN EXEMPTION UNDER
            APPLICABLE STATE LAW OR PURSUANT TO RULE 144 OR AN OPINION OF
            COUNSEL REASONABLY SATISFACTORY TO THE CORPORATION AND ITS COUNSEL
            THAT SUCH REGISTRATION IS NOT REQUIRED.

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            5.3 Compliance with Securities Laws on Transfer. This Warrant and
the Shares issuable upon exercise of this Warrant (and the securities issuable,
directly or indirectly, upon conversion of the Shares, if any) may not be
transferred or assigned in whole or in part without compliance with applicable
federal and state securities laws by the transferor and the transferee
(including, without limitation, the delivery of investment representation
letters and legal opinions reasonably satisfactory to the Company, as reasonably
requested by the Company). The Company shall not require Holder to provide an
opinion of counsel if the transfer is to an affiliate of Holder or if there is
no material question as to the availability of current information as referenced
in Rule 144(c), Holder represents that it has complied with Rule 144(d) and (e)
in reasonable detail, the selling broker represents that it has complied with
Rule 144(f), and the Company is provided with a copy of Holder's notice of
proposed sale.

            5.4 Transfer Procedure. Subject to the provisions of Section 5.3,
Holder may transfer all or part of this Warrant or the Shares issuable upon
exercise of this Warrant (or the securities issuable, directly or indirectly,
upon conversion of the Shares, if any) at any time to Silicon Valley Bancshares
or The Silicon Valley Bank Foundation, or to any affiliate of Holder, or, to any
other transferee by giving the Company notice of the portion of the Warrant
being transferred with the name, address and taxpayer identification number of
the transferee and surrendering this Warrant to the Company for reissuance to
the transferee(s) (and Holder if applicable). The Company may refuse to transfer
this Warrant to any person who directly competes with the Company unless the
Company's stock is publicly traded.

            5.5 Notices. All notices and other communications from the Company
to the Holder, or vice versa, shall be deemed delivered and effective when given
personally or mailed by first-class registered or certified mail, postage
prepaid, at such address as may have been furnished to the Company or the
Holder, as the case may be, in writing by the Company or such holder from time
to time. All notices to the Holder shall be addressed as follows:

                   Silicon Valley Bank
                   Attn: Treasury Department
                   3003 Tasman Drive, HG 110
                   Santa Clara, CA 95054

            5.6 Waiver. This Warrant and any term hereof may be changed, waived,
discharged or terminated only by an instrument in writing signed by the party
against which enforcement of such change, waiver, discharge or termination is
sought.

            5.7 Attorney's Fees. In the event of any dispute between the parties
concerning the terms and provisions of this Warrant, the party prevailing in
such dispute shall be entitled to collect from the other party all costs
incurred in such dispute, including reasonable attorney's fees.

            5.8 Governing Law. This Warrant shall be governed by and construed
in accordance with the laws of the State of California, without giving effect to
its principles regarding conflicts of law.

                                "COMPANY" STENTOR, INC.

                                By: [Signature by Authorized Agent]
                                   _____________________________________________

                                Name:___________________________________________
                                     (Print)
                                Title: Chairman of the Board, President or
                                       Vice President

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                             By: [Signature by Authorized Agent]
                                ________________________________________________

                             Name:______________________________________________
                                   (Print)
                             Title: Chief Financial Officer, Secretary,
                                    Assistant Treasurer or Assistant
                                    Secretary

                              "HOLDER" Silicon Valley Bank

                              By: [Signature by Authorized Agent]
                                 _______________________________________________

                              Name:_____________________________________________

                              Title:____________________________________________

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                                   APPENDIX 1

                               NOTICE OF EXERCISE

      1. Holder elects to purchase _________ shares of the Common/Series _____
Preferred [strike one] Stock of STENTOR, INC. pursuant to the terms of the
attached Warrant, and tenders payment of the purchase price of the shares in
full.

      1. Holder elects to convert the attached Warrant into Shares/cash [strike
one] in the manner specified in the Warrant. This conversion is exercised for
_______________________ of the Shares covered by the Warrant.

      [Strike paragraph that does not apply.]

      2. Please issue a certificate or certificates representing the shares in
the name specified below:

               ___________________________________
                    Holders Name

               ___________________________________

               ___________________________________
                    (Address)

      3. The undersigned represents it is acquiring the shares solely for its
own account and not as a nominee for any other party and not with a view toward
the resale or distribution except in compliance with applicable securities laws.

                                                HOLDER:

                                                ________________________________

                                                By:_____________________________

                                                Name:___________________________

                                                Title:__________________________

_____________________
      (Date)

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