Document:

EXHIBIT 4.1

                         AMENDMENT TO RIGHTS AGREEMENT

         This Amendment dated as of January 12, 2004 (the "Amendment"), to the
Rights Agreement (the "Rights Agreement"), dated as of March 7, 2003, between
TheraSense, Inc., a Delaware corporation (the "Company"), and ComputerShare
Investor Services, as Rights Agent (the "Rights Agent"), is being executed at
the direction of the Company, by and between the Company and the Rights Agent.
Capitalized terms used without definition in this Amendment shall have the
meanings ascribed to such capitalized terms used in the Rights Agreement.

         WHEREAS, the Company, Abbott Laboratories, an Illinois corporation
("Parent"), and Corvette Acquisition Corp., a Delaware corporation and a
wholly-owned subsidiary of Parent ("Sub"), intend to enter into an Agreement
and Plan of Merger (the "Merger Agreement") pursuant to which Parent, Sub and
the Company will agree to enter into a business combination by means of the
merger of Sub with and into the Company (the "Merger") upon the terms and
subject to the conditions set forth in the Merger Agreement;

         WHEREAS, in connection with the Merger Agreement, Parent, Sub and
certain stockholders of the Company intend to enter into a stockholder
agreement (the "Stockholder Agreement") pursuant to which, among other things,
such stockholders will agree to vote to approve and adopt the Merger Agreement
and the Merger and to take certain other actions in furtherance of the Merger,
upon the terms and subject to the conditions set forth in the Stockholder
Agreement;

         WHEREAS, on January 12, 2004, the Board of Directors of the Company
resolved to amend the Rights Agreement to render the Rights (as defined in the
Rights Agreement) inapplicable to the Merger and the other transactions
contemplated by the Merger Agreement and Stockholder Agreement; and

         WHEREAS, the Company wishes to supplement and amend the Rights
Agreement, as permitted by Section 23 thereof, to render the Rights Agreement
inapplicable to the Merger Agreement, the Stockholder Agreement, the Merger and
the other transactions contemplated by the Merger Agreement and the Stockholder
Agreement.

         NOW, THEREFORE, in consideration of the foregoing and the agreements,
provisions and covenants contained in this Amendment, each of the Company and
the Rights Agent agrees as follows:

          1. Amendments to Rights Agreement.
             -------------------------------

                    (a) A new Section 31 is hereby added as follows:

                         "Section 31. Permitted Transactions. Reference is made
                    to the Agreement and Plan of Merger (as it may be amended
                    or supplemented from time to time, the "Merger Agreement")
                    dated as of January 12, 2004 by and among Abbott
                    Laboratories, an Illinois corporation

<PAGE>

                    ("Parent"), Corvette Acquisition Corp., a Delaware
                    corporation and wholly owned subsidiary of Parent ("Sub"),
                    and the Company and the Stockholder Agreement (as it may be
                    amended or supplemented from time to time, the "Stockholder
                    Agreement") dated as of January 12, 2004 by and among
                    Parent, Sub and certain stockholders of the Company. All
                    capitalized terms used in this Section 31 shall have the
                    meanings given to them in the Merger Agreement unless
                    otherwise defined herein. Notwithstanding any other
                    provision of this Agreement to the contrary, neither Parent
                    nor Sub nor any of their respective Affiliates shall be or
                    become an Acquiring Person, and no Distribution Date, Stock
                    Acquisition Date, Section 8(a)(ii) Event or Section 10
                    Event shall occur, and the Rights shall not become
                    exercisable, by reason of (a) the execution of the Merger
                    Agreement or the Stockholder Agreement (or the public
                    announcement thereof), (b) the consummation of the Merger,
                    (c) the conversion of shares of Common Stock into the right
                    to receive the Merger Consideration in accordance with
                    Section 3.1(c) of the Merger Agreement, (d) the
                    consummation of the other transactions contemplated by the
                    Merger Agreement, (e) the agreement pursuant to the
                    Stockholder Agreement of certain stockholders of the
                    Company to vote their shares of Common Stock in favor of
                    the approval and adoption of the Merger Agreement and the
                    Merger, or their granting of irrevocable proxies to Parent
                    to do so, or (f) any other actions taken or effected
                    pursuant to the Stockholder Agreement; and none of the
                    Company, Parent, Sub, the Surviving Corporation or any of
                    their respective Affiliates shall have any obligations
                    under this Agreement to any holder or former holder of
                    Rights as of and following the execution and delivery of
                    the Merger Agreement and the Stockholder Agreement, the
                    consummation of the Merger, the Effective Time or the
                    occurrence of any other events set forth in this sentence;
                    provided, however, that if after the date of execution of
                    the Merger Agreement, the Merger Agreement is terminated in
                    accordance with its terms, this Section 31 shall no longer
                    be applicable with respect to the determination of whether
                    Parent, Sub or any of their respective Affiliates is an
                    Acquiring Person or whether a Distribution Date, Stock
                    Acquisition Date, Section 8(a)(ii) Event or Section 10
                    Event has occurred."

               (b) The definition of "Final Expiration Date" contained in
          Section 1(a) of the Rights Agreement is hereby amended and restated
          in its entirety as follows:

                         "Final Expiration Date" means the earlier of (i) the
                    date and time immediately prior to the Effective Time (as
                    such term is defined in the Merger Agreement referred to in
                    Section 31) and (ii) the close of business on February 25,
                    2013."

     2. Effective Date. This Amendment shall become effective as of the day and
year first written above. Except as modified by this Amendment, the Rights
Agreement shall remain in full force and effect without any modification;
provided,

                                      2
<PAGE>

however, that if after the date of execution of the Merger Agreement, the
Merger Agreement is terminated in accordance with its terms, this Amendment
shall no longer be applicable, and the Rights Agreement, without giving effect
to this Amendment, shall remain in full force and effect.

     3. Certification Pursuant to Section 23 of the Rights Agreement. The
certificate referred to in Section 23 of the Rights Agreement stating that this
Amendment is in compliance with the terms of the Rights Agreement has been
executed by an appropriate officer or director of the Company and is attached
as Annex A hereto.

     4. Inconsistencies. In the event of a conflict or inconsistency between
this Amendment and the Rights Agreement and the exhibits thereto, the
provisions of this Amendment shall govern.

     5. Third Party Beneficiaries. Each of Parent and Sub shall be a third
party beneficiary of this Amendment.

     6. Counterparts. This Amendment may be executed in several counterparts,
each of which shall constitute an original and all of which, when taken
together, shall constitute one agreement.

                              [Signatures Follow]

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be executed and delivered as of the day and year first written above.

                                       THERASENSE, INC.

                                       By: /s/ W. Mark Lortz
                                           -------------------------------------
                                           Name:  W. Mark Lortz
                                           Title: President, Chief Executive
                                                  Officer and Chairman

                                       COMPUTERSHARE INVESTOR SERVICES

                                       By: /s/ Mark Ashbury
                                           -------------------------------------
                                           Name:    Mark Ashbury
                                           Title:   Relationship Manager

<PAGE>

                                                                         ANNEX A

                                THERASENSE, INC.

                       CERTIFICATE PURSUANT TO SECTION 23
                            OF THE RIGHTS AGREEMENT

         I, W. Mark Lortz, Chairman of the Board, President and Chief Executive
Officer of the TheraSense, Inc, a Delaware corporation (the "Company"), do
hereby certify pursuant to Section 23 of the Rights Agreement (the "Rights
Agreement") dated as of March 7, 2003, between the Company and ComputerShare
Investor Services, as Rights Agent, that the proposed amendment to the Rights
Agreement dated January 12, 2004 is in compliance with the terms of the Rights
Agreement.

         IN WITNESS WHEREOF, I have signed this certificate.

Dated:   January 12, 2004

                                     By:
                                         ---------------------------------------
                                         Name:  W. Mark Lortz
                                         Title: Chairman of the Board, President
                                                and Chief Executive Officer<PAGE>
                                                                     Exhibit 4.1

                                S P E C I M E N

     The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations.

<Table>
<S>       <C>                            <C>
TEN COM  - as tenants in common          UNIF GIFT MIN ACT       Custodian
TEN ENT  - as tenants by the entireties                  --------------------
JT TEN   - as joint tenants with the                          (Cust)    (Minor)
            right of suvivorship and             Act
            not as tenants in common                ------------------------
                                                            (State)
</Table>

         Additional abbreviations may also be used though not in the above list.

For value received,                        hereby sell, assign and transfer unto
                   -----------------------
PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE

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(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

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------------------------------------------------------------------------ shares

of the capital stock represented by the within Certificate, and do hereby
irrevocably constitutes and appoint

--------------------------------------------------------------------- , Attorney
to transfer the said stock on the books of the within named Corporation with
full power of substitution in the premises.

Dated
     --------------------

X
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THE SIGNATURE TO THE ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON
THE FACE OF THE CERTIFICATE, IN EVERY PARTICULAR, WITHOUT ALTERATION OR
ENLARGEMENT OR ANY CHANGE WHATSOEVER. THE SIGNATURE(S) MUST BE GUARANTEED BY AN
ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN
ASSOCIATIONS AND CREDIT UNIONS).

SIGNATURE GUARANTEED:
<PAGE>
                                S P E C I M E N

[CITY NETWORK LOGO]

                                  CITY NETWORK

               INCORPORATED UNDER THE LAWS OF THE STATE OF NEVADA
          100,000,000 SHARES COMMON STOCK AUTHORIZED, $0.001 PAR VALUE

  [NUMBER]
                                                           [SHARES]

                                                         CUSIP 178571 10
                                                         SEE REVERSE FOR
                                                       CERTAIN DEFINITIONS

This
certifies
that

is the owner of

            FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK OF
                               CITY NETWORK, INC.

transferable on the books of the Corporation in person or by duly authorized
attorney upon surrender of this certificate properly endorsed. This certificate
and the shares represented hereby are subject to the laws of the State of
Nevada, and to the Articles of Incorporation and Bylaws of the Corporation, as
now or hereafter amended. This certificate is not valid unless countersigned by
the Transfer Agent.

WITNESS the facsimile seal of the Corporation and the signature of its duly
authorized officers.

DATED

/s/                                                     /s/
                              [ S E A L ]
   PRESIDENT                                               SECRETARY

                                       COUNTERSIGNED AND REGISTERED:
                                       PACIFIC STOCK TRANSFER COMPANY,
                                       TRANSFER AGENT AND REGISTRAR

                                       By
                                          -----------------------------
                                              AUTHORIZED SIGNATURE

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