Document:

April 26, 2004

Sushant Mohanty
19609 Bruner Way
Poolesville, MD 20837

RE: Amendment to September 9, 2002 Letter of Employment

Dear Sushant:

This letter hereby amends the Offer Letter between you and Register.com, Inc.
(the "Company"), dated September 9, 2002 (the "Offer Letter").

SECTION 1. AMENDMENTS AND RESTATEMENTS

PARAGRAPH 1. POSITION AND DUTIES
This paragraph is hereby amended and restated in its entirety as follows:

1. Position. You will be employed by the Company as an "at will" employee, with
the title of Chief Information Officer. You will report directly to the Chief
Executive Officer (CEO) of the Company, or such manager as the CEO may designate
from time to time (the "Manager").

PARAGRAPH 2. COMPENSATION
This paragraph is hereby amended and restated in its entirety as follows:

2. Compensation. You will be compensated at the annual rate of $200,000.00
($7,692.31 bi-weekly). This increase in base compensation will be effective May
4, 2004, and will appear in your paycheck beginning on May 24, 2004.

PARAGRAPH 3. BONUS
This paragraph is hereby amended and restated in its entirety as follows:

3. Bonus. You will be eligible to receive an annualized bonus with a target
annual rate of $100,000 based upon your successful performance against goals as
determined by your Manager (as defined in paragraph 1). Your annual bonus is not
necessarily capped at the target amount and may exceed the target based upon
your performance and the company's performance, at the discretion of the CEO.
Your bonus for performance during the 2004 calendar year will be calculated
based on your performance in your existing position through May 3, 2004 and your
performance as Chief Information Officer from May 4, 2004 through December 31,
2004 and a pro rata calculation of the bonus targets related to each role. The
minimum annual bonus in any year (including year 2004) that will be paid is
$50,000. You must be actively employed by the Company at the time of payment (at
such time as bonuses are regularly paid to senior managers) to receive any
Bonus, except that if your employment is terminated (a) without Cause (as
defined below), (b) as a result of a change in control of the Company, as
defined in change in control documents currently in effect in the Company, or
(b) if you resign for "Good Reason" as defined below, you will receive a
pro-rated portion of your bonus based upon the number of months you worked in
that calendar year, and taking into account your performance and the Company's
performance for that year. All bonus payments are subject to applicable
withholdings.

For purposes of this letter agreement, "Good Reason" means, without your written
consent, (i) a change in your reporting relationship to CEO; (ii) any material
diminution in the scope of your duties and/or responsibilities as Chief
Information Officer; (iii) a change in your title to other than Chief
Information Officer; or (iv) a reduction by the Company of your annual rate of
base salary from the then-current annual rate of base salary, unless all other
senior executives undergo substantially equivalent reductions. You must give the
Company thirty (30) days' written notice and opportunity to cure prior to any
resignation for Good Reason for grounds specified in (i) through (iv) above.

PARAGRAPH 4. VACATION
This paragraph is hereby amended and restated in its entirety as follows:

4. Vacation. You will be eligible to receive three weeks' paid vacation for
every year that you work. Vacation entitlement will increase according to the
Company's vacation schedule, but in no event shall you receive less than three
weeks of vacation for every year that you work.

PARAGRAPH 6. STOCK OPTIONS
This paragraph is hereby amended by adding the following:

6. Stock Options. In connection with your promotion to Chief Information
Officer, subject to approval of the Board Committee, you shall receive the
rights (the "Options") to purchase an aggregate of 75,000 shares of common stock
of the Company (the "Option

Shares") at the closing price of the Company's common stock on NASDAQ on the day
the Board Committee approves the grant. The Options shall be granted no later
than 10 business days from acceptance of this agreement. The Option Shares shall
be governed and vest in accordance with the standard company stock option plan
and policy in effect.

PARAGRAPH 7. BEST EFFORTS:
This paragraph is hereby amended and restated in its entirety as follows:

7. Best efforts. You agree that so long as you are employed by the Company you
will diligently and faithfully devote full efforts and working time to the
affairs of the Company and will not accept any other employment, including
consulting work, or engage in any other business activity. You also agree that
you will spend your time at the Company's New York and Maryland office as
appropriate to adequately perform functions of your job and meet the business
needs of the company.

PARAGRAPH 8. NOTICE.
The following paragraph is hereby added in its entirety as follows:

8. This Is Not A Contract of Employment. Notwithstanding any provision of this
agreement, either party can terminate Employee's employment at any time with or
without cause. A 30 days advance notice of termination by either party is to be
given to the other party; provided, however, the Company shall not be required
to provide any prior notice where the Employee's employment is being terminated
for "Cause." For purposes of this letter, "Cause" is defined as (i) your breach
of the terms of your employment or proprietary information agreement; (ii) your
commission of any felony or any crime involving moral turpitude; (iii) your
breach of a fiduciary duty or material policy of the Company; (iv) your
commission of a dishonest act or common law fraud against the Company; (v) gross
negligence or willful misconduct in connection with your position, (vi) your
continual failure or refusal to perform any duties reasonably required in the
course of your employment; (vii) your refusal to take or failure to
satisfactorily complete any screening test for illegal drugs and controlled
substances that may be administered; or (viii) your engagement in misconduct in
bad faith which is materially injurious to the Company.

PARAGRAPH 9. SEVERANCE.

The following paragraph is hereby added in its entirety as follows:

9. Notwithstanding that your status is as an at-will employee, (a) in the event
that the Company terminates your employment without Cause or (b) you terminate
your employment for Good Reason, you will be eligible to receive the base salary
to which you would have been entitled to receive for a period of three (3)
months from the effective date of termination.

SECTION 2. MISCELLANEOUS

The Offer Letter as modified hereby and the Proprietary Information, Inventions and
Non-Solicitation Agreement previously signed by you shall remain in full force
and effect. You acknowledge and agree that the Offer Letter as hereby amended
represents the complete understanding of the terms of your employment and you
are not relying on any discussions or agreements outside of the Offer Letter as
hereby amended. You also agree that nothing contained in this amendment or in
your original offer letter shall be deemed to alter your status as an "at-will"
employee.

If the above accurately reflects our agreement, kindly so signify by signing the
enclosed copy of this letter in the space provided below and returning it to the
undersigned.

Sushant Mohanty                                      Register.com, Inc.

/s/ Sushant Mohanty                                  /s/ Peter Forman
-------------------                                  ----------------
                                                     Peter Forman
                                                     President & CEO<PAGE>
                                                                     Exhibit 4.2

                           SECOND AMENDED AND RESTATED
                             STOCKHOLDERS' AGREEMENT

      This Second Amended and Restated Stockholders' Agreement (this
"Agreement") is entered into as of the 17th day of December, 2002, by and among
Stereotaxis, Inc., a Delaware corporation (the "Company"), persons under the
Existing Stockholders' Agreement (as defined below) holding at least 50% of the
Voting Securities (as such term is defined in the Existing Stockholders'
Agreement), and the Series D-2 Preferred Holders (as defined below) (hereinafter
sometimes referred to individually as a "Stockholder" and collectively as the
"Stockholders"). Stockholders that own the Company's Series A Preferred Stock
are referred to herein as the "Series A Preferred Holders"; Stockholders that
own the Company's Series B Preferred Stock are referred to herein as the "Series
B Preferred Holders"; Stockholders that own the Company's Series C Preferred
Stock are referred to herein as the "Series C Preferred Holders"; Stockholders
that own the Company's Series D Preferred Stock are referred to herein as the
"Series D Preferred Holders"; Stockholders that own the Company's Series D-1
Preferred Stock are referred to herein as the "Series D-1 Preferred Holders";
Stockholders that own (or that have agreed to purchase) the Company's Series D-2
Preferred Stock are referred to herein as the "Series D-2 Preferred Holders."

      WHEREAS, the Series D-2 Preferred Holders have agreed to purchase certain
shares of the Company's Series D-2 Preferred Stock (together with the underlying
shares of the Company's common stock issued upon conversion of such shares, the
"Series D-2 Preferred Stock") pursuant to that certain Series D-2 Preferred
Stock Purchase Agreement dated of even date herewith (the "Purchase Agreement")
provided that the parties hereto enter into this Agreement.

      WHEREAS, the Company, the Series A Preferred Holders, the Series B
Preferred Holders, the Series C Preferred Holders, the Series D Preferred
Holders and the Series D-1 Holders have previously entered into that certain
Amended and Restated Stockholders' Agreement dated as of November 21, 2001 (the
"Existing Stockholders' Agreement").

      WHEREAS, in order to induce the Series D-2 Preferred Holders to purchase
the Series D-2 Preferred Stock, the Company and the Stockholders deem it
desirable to enter into this Stockholders' Agreement, which shall supersede the
Existing Stockholders' Agreement and shall amend and restate certain obligations
of the parties to such agreement as provided for herein.

      1.    Supersedes. Upon the execution and delivery hereof by holders of not
less than 50% of the Voting Securities under the Existing Stockholders'
Agreement, this Agreement shall supersede and replace such Existing
Stockholders' Agreement.

      2.    Election of Directors. (a) Each Stockholder agrees to take all
action necessary, including, without limitation, the voting of their shares of
stock of the Company, the execution of written consents, the calling of special
meetings, the removal of directors, the filling of vacancies on the Company's
Board of Directors, the waiving of notice and the attending of meetings, so as
to cause the authorized number of directors on the Board of Directors of the
Company to be
<PAGE>
established at ten (10) directors (each a "Director" and collectively, the
"Directors"), and consisting of the following individuals:

            (i)   one (1) director who has been selected by the holders of a
majority of the Series A Preferred Stock (the "Series A Director");

            (ii)  one (1) director who has been selected by the holders of a
majority of the Series B Preferred Stock (the "Series B Director");

            (iii) one (1) director who has been selected by Gateway Venture
Partners III, L.P. so long as it owns shares of Series B Preferred or common
stock issued upon conversion thereof (the "Gateway Director");

            (iv)  one (1) director who has been selected by CID so long as it
owns shares of Series C Preferred or common stock issued upon conversion thereof
(the "CID Director");

            (v)   one (1) director who has been selected by Advent International
Corporation or a designee of Advent so long as it owns shares of Series D
Preferred or common stock issued upon conversion thereof (the "Advent
Director");

            (vi)  one (1) director who has been selected by Ampersand Ventures
so long as it owns shares of Series D Preferred or common stock issued upon
conversion thereof (the "Ampersand Director");

            (vii) one (1) director who has been selected by the holders of a
majority of the Series D-1 Preferred Stock (the "Series D-1 Director");

            (viii) the Company's Chief Executive Officer; and

            (ix)  two individuals designated jointly by the foregoing directors;
provided, however, that in the event the Company issues and sells not fewer than
an aggregate of 9,200,000 shares of its Series D-2 Preferred, then one of such
two individuals shall be selected by the holders of a majority of the Series D-2
Preferred Stock (such individual, the "Series D-2 Director").

      (b)   At the time of this Agreement, the Series A Director is Fred
Middleton, the Series B Director is Randall D. Ledford, the Gateway Director is
Gregory D. Johnson, the CID Director is John C. Aplin, the Advent Director is
William C. Mills III, the Ampersand Director is David J. Parker, the Series D-1
Director is Christopher Alafi, the director who is the Company's Chief Executive
Officer is Bevil J. Hogg, and the other two directors are Matthew Howard and
William M. Kelley. Subject to Section 3, each director shall have the option to
be appointed to any committees of the Board of Directors, whether now existing
or hereinafter created, on an equal basis as each other member of the Board of
Directors and otherwise consistent with the fiduciary duties of the members of
the Board of Directors.

      3.    Committees of the Board. The Company shall take such actions as are
reasonably necessary to cause, and the Stockholders shall cause their
director-designees to vote in favor of,

                                       2
<PAGE>
the appointment of the Ampersand Director as a member of the Company's
Compensation Committee and the appointment of the Advent Director as a member of
the Company's Audit Committee.

      4.    Meetings of the Board of Directors; Director Expenses;
Indemnification.

            (a) The Company agrees to furnish to each Director written notice of
and an agenda prior to each regularly scheduled meeting of the Board of
Directors or any committee thereof. The Company shall provide each Director with
a copy of all notices, agendas, and minutes of all meetings of the Board of
Directors, including reports given to or prepared by the Board of Directors or
any committee thereof. The Company shall pay all reasonable travel expenses of
each Director related to attending meetings of the Board of Directors or
committees thereof. The Board of Directors shall meet at least once every three
months.

      (b)   Advent and Ampersand, and each Stockholder owning at least 300,000
shares of the Company's Voting Securities, shall have the right, from time to
time, to designate one of their representatives to attend any meeting of the
Board of Directors as an observer and at the expense of such Stockholder, upon
reasonable advance notice to the Company. As used herein, "Voting Securities"
shall mean the Company's: (i) Common Stock, $.001 par value; and (ii) Series A,
Series B, Series C, Series D Series D-1 and/or Series D-2 Preferred Stock, $.001
par value, and any other security of the Company entitled to vote on the
election of board of directors of the Company pursuant to the Company's
Certificate of Incorporation or Delaware law.

      (c)   The Company shall indemnify each Director to the fullest extent
permitted by law and shall enter into indemnification agreements with each
Director reasonably acceptable to the Company and the Directors with respect
thereto.

      5.    Representations and Warranties.  Each Stockholder represents
and warrants to the other Stockholders, and the Company represents to the
Stockholders, the following with respect to himself, herself or itself, as
the case may be:

            (a)   Authorization. The Company and each Stockholder has the right
and legal capacity to execute, deliver and perform his, her or its obligations
under this Agreement. This Agreement is a legal, valid and binding obligation of
the Company and each such Stockholder, enforceable against the Company and such
Stockholder in accordance with its terms.

            (b)   No Violation. The execution and delivery of this Agreement
will not (with or without notice or passage of time or both) (i) conflict with
or result in a breach of any provision of the certificate of incorporation or
bylaws (or similar governing documents) of the Company or the Stockholder (if an
entity), (ii) result in a default, give rise to any right of termination,
cancellation or acceleration, or require any consent or approval, under any of
the terms, conditions or provisions of any note, bond, mortgage, indenture,
loan, factoring arrangement, license, agreement, lease or other instrument or
obligation to which the Company or each such Stockholder is a party or by which
it or any of its assets may be bound (other than the Existing Stockholders'
Agreement (which agreement is being superseded hereby)) or (iii)

                                       3
<PAGE>
violate any law, judgment, order, writ, injunction, decree, statute, rule or
regulation of any court, administrative agency, bureau, board, commission,
office, authority, department or other governmental entity applicable to the
Company or such Stockholder or any of its assets.

      6.    Term. This Agreement shall terminate and be of no further force or
effect upon the earliest to occur of (a) the closing of a public offering of
shares of the Company's capital stock pursuant to a registration statement filed
by the Company under the Securities Act of 1933, as amended, which has become
effective thereunder (other than a registration statement relating solely to
employee benefit plans or a transaction covered by Rule 145 of the Securities
and Exchange Commission), (b) the time that the Company becomes required to file
reports with the Securities and Exchange Commission under Sections 12(g) or
15(d) of the Securities Exchange Act of 1934, as amended, or (c) upon any change
in control of the Company as set forth in the following sentence. A "change of
control" of the Company shall be deemed to occur upon (i) any consolidation or
merger of the Company with or into any other corporation or other entity or
person, or any other corporate reorganization in which the Company shall not be
the continuing or surviving entity of such consolidation, merger or
reorganization or any transaction or series of related transactions by the
Company in which in excess of 50% of the Company's voting securities are
transferred, or (ii) a sale, lease, license or other disposition of all or
substantially all of the assets of the Company.

      7.    Consent to Amendments; Waivers. Any term of this Agreement may be
modified, amended or waived only upon the written agreement of the Company, and
Stockholders holding at least fifty percent (50%) of the Voting Securities held
by the Stockholders at the time of such amendment or waiver. In addition, any
modification, amendment or waiver which adversely affects any class of Voting
Securities (including, without limitation, any modification, amendment or waiver
of the provisions of Section 2 hereof adversely affecting such class of Voting
Securities), or the specific rights of Gateway, CID, Advent or Ampersand as set
forth herein, requires the written Agreement of 50% of the holders of the
adversely affected class or Gateway, CID, Advent or Ampersand, as the case may
be. Any waiver, permit, consent or approval of any kind or character on the part
of any such Stockholder of any provisions or conditions of this Agreement must
be made in writing and shall be effective only to the extent specifically set
forth in such writing.

      8.    Legend. The Corporation will stamp or imprint each certificate or
other instrument representing Voting Securities, throughout the term of this
Agreement, with a legend in substantially the following form:

            "THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO THE
            TERMS OF A STOCKHOLDERS' AGREEMENT, AS AMENDED OR RESTATED FROM TIME
            TO TIME, BETWEEN THE HOLDER AND THE CORPORATION, A COPY OF WHICH MAY
            BE OBTAINED FROM THE SECRETARY OF THE CORPORATION."

      9.    Governing Law. This Agreement shall be governed by and construed
under the laws of the State of Delaware without regard to its choice of law
provisions.

                                       4
<PAGE>
      10.   Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

      11.   Titles and Subtitles. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

      12.   Notices. Any notice required or permitted under this Agreement shall
be given in writing and shall be deemed effectively given upon personal delivery
or upon deposit with the United States Post Office, by registered or certified
mail, postage prepaid, addressed to the Company at Stereotaxis, Inc., 4041
Forest Park Avenue, St. Louis, Missouri 63108, with a copy to James L. Nouss,
Jr., Esq., Bryan Cave LLP, One Metropolitan Square, 211 N. Broadway, Ste. 3600,
St. Louis, Missouri, 63102, and if to any Stockholder, at the respective
addresses set forth in the stock records of the Company, or at such other
address as any party may designate by 10 days' advance written notice to the
other party.

      13.   Benefit of Parties; Assignability. All of the terms and provisions
of this Agreement shall be binding upon and shall inure to the benefit of the
parties and their respective personal representatives, heirs, successors and
assigns, including without limitation all subsequent holders of securities who
become bound by the terms of this Agreement; provided, however, that neither the
Company nor any Stockholder may delegate its responsibilities or assign or
transfer its rights or obligations under this Agreement without the prior
written consent of Advent and Ampersand.

      14.   Cooperation. The parties agree that after execution of this
Agreement they will from time to time, upon the request of any other party and
without further consideration, execute, acknowledge, and deliver in proper form
any further instruments and take such other action as any other party may
reasonably require to carry out effectively the intent of this Agreement.

                                  * * * * * * *

                                       5
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have executed this Amended and
Restated Stockholders' Agreement as of the date first above written.

                                   STEREOTAXIS, INC.

                                   By: /s/ BEVIL J. HOGG
                                      -----------------------------------------
                                      Bevil J. Hogg, President

                                   AMPERSAND 1999 LIMITED PARTNERSHIP
                                   By:  AMP-99 Management Company
                                        Limited Liability Company, its
                                        General Partner

                                   By: /s/ DAVID J. PARKER
                                      -----------------------------------------
                                        David J. Parker
                                        Managing Member

                                   AMPERSAND 1999 COMPANION FUND
                                   LIMITED PARTNERSHIP
                                   By:  AMP-99 Management Company
                                        Limited Liability Company, its
                                        General Partner

                                   By: /s/ DAVID J. PARKER
                                      -----------------------------------------
                                        David J. Parker
                                        Managing Member

                                   ADVENT HEALTHCARE AND LIFE SCIENCES
                                   II LIMITED PARTNERSHIP
                                   By: Advent International Limited Partnership,
                                       General Partner

                                   By:  Advent International Corporation,
                                        General Partner

                                   By: /s/ WILLIAM C. MILLS III
                                      -----------------------------------------
                                        William C. Mills III
                                        Vice President

                                       6
<PAGE>
                                   ADVENT HEALTHCARE AND LIFE SCIENCES
                                   II BETEILIGUNG GMBH & CO. KG
                                   By:  Advent International Limited
                                        Partnership, Managing Limited
                                        Partner

                                   By:  Advent International Corporation,
                                        General Partner

                                   By: /s/ WILLIAM C. MILLS III
                                      -----------------------------------------
                                        William C. Mills III
                                        Vice President

                                   ADVENT PARTNERS HLS II LIMITED PARTNERSHIP

                                   By:  Advent International Corporation,
                                        General Partner

                                   By: /s/ WILLIAM C. MILLS III
                                      -----------------------------------------
                                        William C. Mills III
                                        Vice President

                                   ADVENT PARTNERS LIMITED PARTNERSHIP
                                   By:  Advent International Corporation,
                                        General Partner

                                   By: /s/ WILLIAM C. MILLS III
                                      -----------------------------------------
                                        William C. Mills III
                                        Vice President

                                   EGS PRIVATE HEALTHCARE PARTNERSHIP, L.P.

                                   By: /s/ ABHIJEET LELE
                                      -----------------------------------------
                                      Name:  Abhijeet Lele
                                      Title: Managing Director

                                       7
<PAGE>
                                   EGS PRIVATE HEALTHCARE COUNTERPART, L.P.

                                   By: /s/ ABHIJEET LELE
                                      -----------------------------------------
                                      Name:  Abhijeet Lele
                                      Title:  Managing Director

                                   ADVANTAGE CAPITAL MISSOURI PARTNERS III, L.P.
                                   By:  Advantage Capital Company MO-GP-III,
                                        L.L.C., its general partner

                                   By: /s/ SCOTT ZAJAC
                                      -----------------------------------------
                                      Name:
                                      Title:

                                   ADVANTAGE CAPITAL MISSOURI PARTNERS I, L.P.

                                   ADVANTAGE CAPITAL MISSOURI PARTNERS II, L.P.

                                   By: /s/ SCOTT ZAJAC
                                      -----------------------------------------
                                      Name:
                                      Title:

                                   A.G.E. INVESTMENTS, INC.

                                   By: /s/ DOUGLAS L. KELLY
                                      -----------------------------------------
                                      Name: Douglas L. Kelly
                                      Title: Director

                                   ALAFI CAPITAL COMPANY, LLC

                                   By: /s/ MOSHA ALAFI
                                      -----------------------------------------
                                      Name: Mosha Alafi
                                      Title: Managing Partner

                                       8
<PAGE>
                                   CHRISTOPHER ALAFI, an individual

                                        /s/  CHRISTOPHER ALAFI
                                   -----------------------------------------
                                     Christopher Alafi

                                   ASCENSION HEALTH, as Fiscal Agent and
                                     Nominee of certain of its wholly-owned
                                     subsidiaries

                                   By: /s/   DOUGLAS D. FRENCH
                                      -----------------------------------------
                                      Name:    Douglas D. French
                                      Title:   President & CEO

                                   EMERSUB XXXVIII, INC.

                                   By:    /s/  HARLEY M. SMITH
                                      -----------------------------------------
                                      Name:  Harley M. Smith
                                      Title: Vice President and Secretary

                                   FERI TRUST GMBH

                                   By:    /s/  MICHAEL STAMMLER
                                      -----------------------------------------
                                      Name:    Michael Stammler
                                      Title:   Partner

                                   BOME INVESTORS III, L.L.C.
                                   By:  GATEWAY CAPCO III, L.L.C.,
                                        its Attorney-in-Fact

                                   By:    /s/ GREGORY R. JOHNSON
                                      -----------------------------------------
                                      NAME:  Gregory R. Johnson
                                      Title: Member

                                       9
<PAGE>
                                   BOME INVESTORS II, LLC
                                   By:  GATEWAY CAPCO, LLC,
                                        its Attorney-in-Fact

                                   By:  /s/  GREGORY R. JOHNSON
                                      -----------------------------------------
                                      Name:  Gregory R. Johnson
                                      Title: Member

                                   BOME INVESTORS, INC.
                                   By:  GATEWAY CAPCO, LLC,
                                        its Attorney-in-Fact

                                   By:  /s/  GREGORY R. JOHNSON
                                      -----------------------------------------
                                      Name:  Gregory R. Johnson
                                      Title: Member

                                   GATEWAY VENTURE PARTNERS III, L.P.
                                   By:  Gateway Associates III, L.P.,
                                        its General Partner

                                   By:  /s/  GREGORY R. JOHNSON
                                      -----------------------------------------
                                      Name:  Gregory R. Johnson
                                      Title: Member

                                   GRAYSTONE VENTURE DIRECT EQUITY, L.P.
                                   By:  Graystone Venture Partners,
                                        LLC, its general partner

                                   By:  /s/  JUDITH BULTMAN MEYER
                                      -----------------------------------------
                                        Judith Bultman Meyer
                                        Managing Director

                                       10
<PAGE>
                                   PORTAGE FOUNDERS, L.P.
                                   By:  Portage Venture Partners,
                                        L.L.C., its General Partner

                                   By:
                                      -----------------------------------------
                                        Judith Bultman Meyer
                                        Managing Director

                                   PORTAGE VENTURE FUND, L.P.
                                   By:  Portage Venture Partners,
                                        L.L.C., its General Partner

                                   By:
                                      -----------------------------------------
                                        Judith Bultman Meyer
                                        Managing Director

                                   SANDERLING VENTURES LIMITED, L.P.
                                   SANDERLING VENTURE PARTNERS II, L.P.
                                   SANDERLING VENTURE PARTNERS IV CO-
                                     INVESTMENT FUND, L.P.
                                   SANDERLING IV BIOMEDICAL CO-INVESTMENT
                                     FUND, L.P.
                                   SANDERLING II LIMITED PARTNERSHIP
                                   SANDERLING VENTURE PARTNERS V CO-INVESTMENT
                                     FUND, L.P.
                                   SANDERLING V BETEILIGUNGS GMBH & CO. KG
                                   SANDERLING V LIMITED PARTNERSHIP
                                   SANDERLING V BIOMEDICAL CO-INVESTMENT
                                     FUND, L.P.
                                   SANDERLING VENTURES MANAGEMENT V

                                   By:
                                      -----------------------------------------
                                      Name:  Fred A. Middleton
                                      Title:  General Partner

                                       11
<PAGE>

                                        /s/  FRED A. MIDDLETON
                                   -----------------------------------------
                                   Fred A. Middleton

                                        /s/   ROBERT G. MCNEIL
                                   -----------------------------------------
                                   Robert G. McNeil

                                        /s/  PAULETTE J. TAYLOR
                                   -----------------------------------------
                                   Paulette J. Taylor

                                   CID EQUITY CAPITAL V, L.P.
                                   By:  CID Equity Partners V,
                                        Its general partner

                                   By:  /s/  JOHN C. APLIN
                                      -----------------------------------------
                                        John C. Aplin, General Partner

                                   MITSUBISHI INTERNATIONAL CORPORATION

                                   By:  /s/  MOTOATSU SAKURAI
                                      -----------------------------------------
                                      Name:  Motoatsu Sakurai
                                      Title: Executive Vice President & COO

                                   MIC CAPITAL LLC
                                   By:  MC Financial Services Ltd., as Manager

                                   By:  /s/  SHUNICHI MAEDA
                                      -----------------------------------------
                                      Name:  SHUNICHI MAEDA
                                      Title: President

                                   STIFEL CAPCO II, L.L.C.

                                   By:  /s/  J. JOSEPH SCHLAFLY
                                      -----------------------------------------
                                      Name:  J. Joseph Schlafly
                                      Title: President

                                       12
<PAGE>
                                   EDWIN B. MONROE AND CAROLE S. MONROE,
                                   JOINT TENANTS WITH RIGHT OF
                                   SURVIVORSHIP

                                   By:  /s/  EDWIN B. MONROE
                                      -----------------------------------------
                                      Name:  Edwin B. Monroe

                                   By:  /s/ CAROLE S. MONROE
                                       -----------------------------------------
                                      Name:  Carole S. Monroe

                                   DAVID T. ERICKSON AND NANCY V.
                                   ERICKSON, JOINT TENANTS WITH RIGHT OF
                                   SURVIVORSHIP

                                   By:  /s/  DAVID T. ERICKSON
                                      -----------------------------------------
                                      Name:  David T. Erickson

                                   By:  /s/  NANCY V. ERICKSON
                                      -----------------------------------------
                                      Name:  Nancy V. Erickson

                                       13
<PAGE>
                                   PROLOG CAPITAL A, L.P.
                                   By:  Prolog Ventures A, LLC
                                        Its General Partner

                                   By: /s/ GREGORY R. JOHNSON
                                      -----------------------------------------
                                      Name:  Gregory R. Johnson
                                      Title:  A Managing Director

                                   PROLOG CAPITAL B, L.P.
                                   By:  Prolog Ventures B, LLC
                                        Its General Partner

                                   By: /s/ GREGORY R. JOHNSON
                                      -----------------------------------------
                                      Name:  Gregory R. Johnson
                                      Title:  A Managing Director

                                       14
<PAGE>
                                   MITSUBISHI CORPORATION

                                   By: /s/ TERUYUKI NAKAZAWA
                                      -----------------------------------------
                                      Name: Teruyuki Nakazawa
                                      Title: General Manager
                                             Technology & Business Development

                                       15

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