Document:

<PAGE>

                                                                   EXHIBIT 10.1

                              FIRST AMENDMENT TO

                            EXCLUSIVE MARKETING AND

                            DISTRIBUTION AGREEMENT

                                   BETWEEN

                        NORTH AMERICAN SCIENTIFIC, INC.

                                     AND

                              MENTOR CORPORATION

<PAGE>

                              FIRST AMENDMENT TO
                EXCLUSIVE MARKETING AND DISTRIBUTION AGREEMENT
                                  BETWEEN
                       NORTH AMERICAN SCIENTIFIC, INC.
                                    AND
                             MENTOR CORPORATION

THIS FIRST AMENDMENT, dated for reference purposes as of February 24, 1999,
pertains to that certain Exclusive Marketing and Distribution Agreement (the
"Agreement"), dated for reference purposes as of June 16, 1997, between NORTH
AMERICAN SCIENTIFIC, INC., a Delaware corporation ("NAMS") and MENTOR
CORPORATION, a Minnesota corporation ("MENTOR") and is made with reference to
the following facts:

RECITALS

     A.  Sections 1.28 and 2.3 of the Agreement contemplate that, if and when
Pd-103 Sources become available, the Products covered by the Agreement will
include Pd-103 Sources subject to the agreement of the parties with respect
to certain terms related thereto.

     B.  NAMS has now obtained 510-K pre-marketing approval from the FDA to
market and sell Pd-103 Sources; and

     C.  Section 7.1.4 of the Agreement contemplates that, if NAMS requires
additional capital to create the manufacturing capacity necessary to produce
Pd-103 Sources, then NAMS shall offer MENTOR the opportunity to provide such
additional required capital on substantially the same terms and conditions as
the Agreement.

     D.  NAMS has estimated that the present capital cost required to create
a manufacturing capacity for ten thousand (10,000) Pd-103 Sources per week is
$1,500,000.

     E.  NAMS also estimates that, if an acceptable commercial supply, as
determined by NAMS, of the Pd-103 isotope (the radioactive source
incorporated into the Pd0-103 Source) cannot be obtained, it would presently
require an additional $2,500,000 for the purchase of linear accelerators that
would enable NAMS to produce the Pd-103 isotope for itself.

     F.  MENTOR is willing to supply so much of the capital as is necessary
to satisfy these capital requirements that NAMS is unable or unwilling to
supply from its own resources in order to preserve the exclusive marketing
and distribution rights for the Pd-103 Sources as contemplated by Section
7.1.4.A. of the Agreement.

                                 AGREEMENTS

     NOW, THEREFORE, the parties hereto, intending to be legally bound, do
hereby agree as follows:

                FIRST AMENDMENT TO MARKETING AGREEMENT: PAGE 1

<PAGE>

1.   DUTY OF NAMS TO CREATE PRODUCTION CAPACITY

     1.1  NAMS covenants and agrees that as soon as practicable after the
execution of this Amendment, NAMS shall develop and maintain the production
capacity (other than the capacity to produce the Pd-103 isotope) necessary to
produce ten thousand (10,000) Pd-103 Sources per week (the "Development
Project").

     1.2  Any subsequent increases in production capacity that are proposed
to be made with capital funding to be provided by MENTOR shall made in
increments of 10,000 Sources per week.

2.   FUNDING OF DEVELOPMENT COSTS

     2.1  Funding by NAMS.  NAMS shall have the right, but not the
obligation, to fund all or any portion of the costs of the Development
Project, including any incremental increases in production capacity.

     2.2  Funding by MENTOR.  MENTOR shall have the obligation to supply to
NAMS any capital required to complete the Development Project (including the
capacity to produce the Pd-103 isotope if NAMS determines to do so) that NAMS
is unwilling or unable to contribute by purchasing shares of the common
capital stock of NAMS (the "Shares"), generally in accordance with the
provisions of the Stock Purchase Agreement between MENTOR and NAMS dated for
reference purposes as of June 16, 1997 and executed by NAMS and MENTOR
simultaneously with their execution of the Agreement (the "Stock Purchase
Agreement").  Should MENTOR provide all or a part of the additional capital
required to fund the Development Project, then:

         2.2.1  Purchase of Capital Stock.  The additional capital
contributed by MENTOR hereunder shall be credited against the purchase price
for shares of the Common Stock of NAMS at a price that is equal to one
hundred ten percent (110%) of the average closing price of the shares of the
common stock of NAMS as reported in the Western Edition of the Wall Street
Journal for the twenty (20) trading days preceding the date on which NAMS
gives a written request to a MENTOR for such additional capital pursuant to
Section 3.3, below.

         2.2.2  Warranties of MENTOR.  MENTOR shall be deemed to have made
all of the warranties and representations to NAMS set forth in Section 7 of
the Stock Purchase Agreement which shall be incorporated herein by reference
as if made on the date on which the Shares are issued to MENTOR.

         2.2.3  Warranties of NAMS.  NAMS shall be deemed to have made all of
the warranties and representations to MENTOR set forth in Section 6 of the
Stock Purchase Agreement, other than those warranties and representations
contained in Sections 6.3, 6.5, and Sections 6.11.1 through 6.11.3 and all
such warranties and representations not expressly excluded by this Section
2.2.4 are incorporated herein by reference as if made on the date on which
the Shares are issued to MENTOR.

                FIRST AMENDMENT TO MARKETING AGREEMENT: PAGE 2

<PAGE>

3.   DEVELOPMENT PROGRAM

     Should NAMS request MENTOR to provide all or a part of the
additional capital required to fund the Development Project, then:

     3.1  Preparation and Approval of Budget.  NAMS shall first prepare and
submit to MENTOR in writing a development plan (the "Development Plan")
containing (a) a line-item budget setting forth the estimated costs of the
Development Project (the "Project Budget") and (b) a schedule of milestones
reflecting the period of time over which the Development Project will be
carried out (the "Development Program").

     3.2  Coordination with MENTOR.  NAMS shall consult with MENTOR in the
preparation of the Development Program, and shall give reasonable
consideration to suggestions and requests made by MENTOR in connection
therewith, but if NAMS and MENTOR are unable to agree with respect to the
budget, milestones or payment schedules for the Development Program, then the
decisions of NAMS shall be final and binding on both parties.

     3.3  Time of Contribution.  MENTOR shall contribute any capital required
to be contributed by it hereunder in cash or immediately available funds
within thirty (30) days after the date on which the Project Budget has been
submitted in accordance with Section 3.1, above, and NAMS shall issue and
deliver to MENTOR share certificates evidencing the Shares being purchased by
MENTOR concurrently with NAMS' receipt of payment therefor.

4.   TERMS SHEET:  PD-103 SOURCES

     There is attached to the Agreement as Schedule 2 a Terms Sheet for
Pd-103 Sources.  NAMS shall supply the Pd-103 Sources to MENTOR, and MENTOR
shall have the exclusive right to market and distribute the Pd-103 Sources in
accordance with the terms and conditions of the Agreement and the Terms Sheet
attached as Schedule 2 to this First Amendment to the Agreement.

5.   FULL FORCE AND EFFECT

     Except as expressly modified by the provisions of this First Amendment
the terms and conditions of the Agreement shall continue in full force and
effect.

                  (Signatures appear on the following page)

                FIRST AMENDMENT TO MARKETING AGREEMENT: PAGE 3

<PAGE>

     IN WITNESS WHEREOF, both parties have executed this First Amendment to
Exclusive Marketing and Distribution Agreement to be duly executed on the
dates set forth below.

Date:  February 24, 1999               Date:  February 24, 1999
     ------------------------               ---------------------------

NORTH AMERICAN SCIENTIFIC INC.         MENTOR CORPORATION,
a Delaware corporation                 a Minnesota corporation

By:    /s/ L. MICHAEL CUTRER           By:  /s/ CHRISTOPHER J. CONWAY
     ------------------------               ---------------------------
       L. Michael Cutrer                        Christopher J. Conway
       Its President                        Its Chief Executive Officer

ADDRESS FOR NOTICES:                   ADDRESS FOR NOTICES:
North American Scientific, Inc.        Mentor Corporation
20200 Sunburst Street                  5425 Hollister Avenue
Chatsworth, California  91311          Santa Barbara, California  93111
PH:  (818) 734-8600                    PH:  (805) 681-6000
FAX: (818) 734-8607                    FAX: (805) 967-3362

                FIRST AMENDMENT TO MARKETING AGREEMENT: PAGE 4

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 SCHEDULE 2

                                TERMS SHEET
                          (NAMS Pd-103 Sources)

                                 REDACTED

                            SCHEDULE 2: PAGE 1

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 REDACTED

                            SCHEDULE 2: PAGE 2

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 REDACTED

                             SCHEDULE 2: PAGE 3

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 REDACTED

                            SCHEDULE 2: PAGE 4

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 REDACTED

                             SCHEDULE 2: PAGE 5

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 REDACTED

                              SCHEDULE 2: PAGE 6

<PAGE>

         CONFIDENTIAL TREATMENT REQUESTED. THE REDACTED MATERIAL HAS
                 BEEN FILED SEPARATELY WITH THE COMMISSION.

                                  REDACTED

                             SCHEDULE 2: PAGE 7<PAGE>
                                                                     EXHIBIT 4.2

NO. WA                         VOID AFTER      , 2006                  WARRANTS
                     CLASS A REDEEMABLE WARRANT CERTIFICATE

                   UNITY EMERGING TECHNOLOGY VENTURE ONE LTD.

THIS CERTIFIES THAT, FOR VALUE RECEIVED                                  CUSIP

or registered assigns (the "Registered Holder") is the owner of the number of
Class A Redeemable Warrants (the "Warrants") specified above. Each Warrant
initially entitles the Registered Holder to purchase, subject to the terms
and conditions set forth in this Certificate and the Warrant Agreement (as
hereinafter defined), one fully paid and nonassessable share of Common Stock,
$.0001 par value, of Unity Emerging Technology Venture One Ltd., a Delaware
corporation (the "Company"), and one Class B Redeemable Warrant of the
Company at any time from the Commencement Date (as hereinafter defined) to
the Expiration Date (as hereinafter defined) upon the presentation and
surrender of this Warrant Certificate with the Subscription Form on the
reverse hereof duly executed, at the corporate office of American Stock
Transfer & Trust Company, 40 Wall Street, New York, New York 10005, as
Warrant Agent, or its successor (the "Warrant Agent"), accompanied by payment
of $5.25, subject to adjustment (the "Purchase Price"), in lawful money of
the United States of America in cash or by check made payable to the Warrant
Agent for the account of the Company.

      This Warrant Certificate and each Warrant represented hereby are issued
pursuant to and are subject in all respects to the terms and conditions set
forth in the Warrant Agreement (the "Warrant Agreement"), dated as of , 2000, by
and between the Company and the Warrant Agent.

      In the event of certain contingencies provided for in the Warrant
Agreement, the Purchase Price and the number of shares of Common Stock and the
number of Class B Redeemable Warrants subject to purchase upon the exercise of
each Warrant represented hereby are subject to modification or adjustment.

      Each Warrant represented hereby is exercisable at the option of the
Registered Holder, but no fractional interests will be issued. In the case of
the exercise of less than all the Warrants represented hereby, the Company shall
cancel this Warrant Certificate upon the surrender hereof and shall execute and
deliver a new Warrant Certificate or Warrant Certificates of like tenor, which
the Warrant Agent shall countersign, for the balance of such Warrants.

      The term "Commencement Date" shall mean the later of (i) , 2001 or (ii)
the date of the consummation of a merger, exchange of capital stock, asset
acquisition or other similar business combination of the Company with an
operating business. The term "Expiration Date" shall mean 5:00 P.M. (New York
City time) on , 2006. If any of such dates shall in the State of New York be a
holiday or a day on which the banks are authorized to close, then such date
shall mean 5:00 P.M. (New York City time) the next following day which in the
State of New York is not a holiday or a day on which banks are authorized to
close.

      The Company shall not be obligated to deliver any securities pursuant to
the exercise of this Warrant unless a registration statement under the
Securities Act of 1933, as amended (the "Act"), with respect to such securities
is effective or an exemption thereunder is available. The Company has covenanted
and agreed that it will file a registration statement under the Federal
securities laws, use its best efforts to cause the same to become effective, to
keep such registration statement current, if required under the Act, while any
of the Warrants are outstanding, and deliver a prospectus which complies with
Section 10(a)(3) of the Act to the Registered Holder

<PAGE>

exercising this Warrant.

      This Warrant shall not be exercisable by a Registered Holder in any state
where such exercise would be unlawful.

      This Warrant Certificate is exchangeable, upon the surrender hereof by the
Registered Holder at the corporate office of the Warrant Agent, for a new
Warrant Certificate or Warrant Certificates of like tenor representing an equal
aggregate number of Warrants, each of such new Warrant Certificates to represent
such number of Warrants as shall be designated by such Registered Holder at the
time of such surrender. Upon due presentment and payment of any tax or other
charge imposed in connection therewith or incident thereto, for registration of
transfer of this Warrant Certificate at such office, a new Warrant Certificate
or Warrant Certificates representing an equal aggregate number of Warrants will
be issued to the transferee in exchange therefor, subject to the limitations
provided in the Warrant Agreement.

      Prior to the exercise of any Warrant represented hereby, the Registered
Holder shall not be entitled to any rights of a stockholder of the Company,
including, without limitation, the right to vote or to receive dividends or
other distributions, and shall not be entitled to receive any notice of any
proceedings of the Company, except as provided in the Warrant Agreement.

      Subject to the provisions of the Warrant Agreement, this Warrant may be
redeemed at the option of the Company and with the prior consent of GBI
Capital Partners Inc., at a redemption price of $.05 per Warrant, at any time
commencing after the Commencement Date, provided that the last sales price of
the Common Stock shall have, for twenty (20) consecutive trading days ending
on the third business day prior to the day that the notice of redemption is
given, equaled or exceeded $8.50 per share (subject to adjustment in the
event of any stock splits or other similar events). Notice of redemption
shall be given not less than the thirtieth day before the date fixed for
redemption, all as provided in the Warrant Agreement. On and after the date
fixed for redemption, the Registered Holder shall have no rights with respect
to this Warrant except to receive the $.05 per Warrant upon surrender of this
Certificate.

      In accordance with the Warrant Agreement, GBI Capital Partners Inc.
shall be entitled to receive a commission equal to 5% of the proceeds
received by the Company from the exercise of the Warrants.

      Prior to due presentment for registration of transfer hereof, the Company
and the Warrant Agent may deem and treat the Registered Holder as the absolute
owner hereof and of each Warrant represented hereby (notwithstanding any
notations of ownership or writing hereon made by anyone other than a duly
authorized officer of the Company or the Warrant Agent) for all purposes and
shall not be affected by any notice to the contrary, except as provided in the
Warrant Agreement.

      This Warrant Certificate shall be governed by and construed in accordance
with the laws of the State of New York without giving effect to conflicts of
laws.

      This Warrant Certificate is not valid unless countersigned by the Warrant
Agent.

      IN WITNESS WHEREOF, the Company has caused this Warrant Certificate to be
duly executed, manually or in facsimile by two of its officers thereunto duly
authorized and a facsimile of its corporate seal to be imprinted hereon.

Dated:                              UNITY EMERGING TECHNOLOGY VENTURE ONE LTD.

<PAGE>

COUNTERSIGNED:                             By:               By:
 AMERICAN STOCK TRANSFER & TRUST COMPANY,
                         as Warrant Agent     /s/Norman Leben    /s/Lawrence
                                                                    Burstein

                        Authorized Officer         SECRETARY         PRESIDENT

                   UNITY EMERGING TECHNOLOGY VENTURE ONE LTD.
                                    CORPORATE
                                      SEAL
                                      2000
                                    DELAWARE
                                        *

<PAGE>

                                SUBSCRIPTION FORM

      To Be Executed by the Registered Holder in Order to Exercise Warrants

      The undersigned Registered Holder hereby irrevocably elects to exercise
_____________ Warrants represented by this Warrant Certificate, and to purchase
the securities issuable upon the exercise of such Warrants, and requests that
certificates for such securities shall be issued in name of

                          PLEASE INSERT SOCIAL SECURITY
                           OR OTHER IDENTIFYING NUMBER
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
                     (please print or type name and address)

and be delivered to
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
                   (please print or type name and address)

and if such number of Warrants shall not be all the Warrants evidenced by this
Warrant Certificate, that a new Warrant Certificate for the balance of such
Warrants be registered in the name of, and delivered to, the Registered Holder
at the address stated below.

Dated:_________________________________    X ___________________________________
                                             ___________________________________
                                             ___________________________________
                                             ___________________________________
                                                          Address

                                             ___________________________________
                                               Social Security or Taxpayer
                                                  Identification Number

                                             ___________________________________
                                                  Signature Guaranteed
                                             ___________________________________

      The undersigned represents that the exercise of the within Warrant was
solicited by GBI Capital Partners Inc. If not solicited by GBI Capital
Partners Inc., please write "unsolicited" in the space below or write the
name of the broker/dealer which solicited your exercise. Unless otherwise
indicated, it will be assumed that the exercise was solicited by GBI Capital
Partners Inc.

                                    ------------------------------------------
                                    (Write "unsolicited" on above line if
                                    not solicited by GBI Capital Partners Inc.)

Dated: _______________________________  Signature: _____________________________

<PAGE>

                                   ASSIGNMENT

      FOR VALUE RECEIVED,
--------------------------------------------------------------------------------
hereby sells, assigns and transfers unto

                        PLEASE INSERT SOCIAL SECURITY OR
                            OTHER IDENTIFYING NUMBER
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
                     (please print or type name and address)

___________________________ of the Warrants represented by this Warrant
Certificate, and hereby irrevocably constitutes and appoints ___________________
________________________________________________________________________________
Attorney to transfer this Warrant Certificate on the books of the Company, with
full power of substitution in the premises.

Dated:  _________________________________        X _____________________________
                                                      Signature Guaranteed

THE SIGNATURE TO THE ASSIGNMENT OR THE SUBSCRIPTION FORM MUST CORRESPOND TO THE
NAME AS WRITTEN UPON THE FACE OF THIS WARRANT CERTIFICATE IN EVERY PARTICULAR,
WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATSOEVER AND MUST BE
GUARANTEED BY A COMMERCIAL BANK OR TRUST COMPANY OR A MEMBER FIRM OF THE
AMERICAN STOCK EXCHANGE, NEW YORK STOCK EXCHANGE, PACIFIC STOCK EXCHANGE OR
MIDWEST STOCK EXCHANGE.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00016-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00016-of-00352.parquet"}]]