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                                                                     Exhibit 4.5

                               THIRD AMENDMENT TO
                     COMMON STOCK PURCHASE WARRANT AGREEMENT

          This Third Amendment to Common Stock Purchase Warrant Agreement, dated
as of October 9, 2000, is between MURDOCK COMMUNICATIONS CORPORATION, an Iowa
corporation (the "Company") and FIRSTAR BANK, N.A., as Warrant Agent and
successor-in-interest to Firstar Trust Company (the "Warrant Agent").

                                    RECITALS

          A. The Warrant Agent and the Company are parties to a Common Stock
Purchase Warrant Agreement dated as of October 21, 1996 (the "Agreement").

          B. The Warrant Agent and the Company entered into a First Amendment to
Warrant Agreement dated as of September 30, 1999, to, among other things, extend
the "Warrant Expiration Date" to April 21, 2000 and a Second Amendment to
Warrant Agreement dated as of April 14, 2000, to extend the "Warrant Expiration
Date" to October 21, 2000.

          C. The Company and the Warrant Agent deem it desirable to amend the
Agreement to extend the "Warrant Expiration Date" to October 21, 2001.

          D. Pursuant to Section 10 of the Agreement, the Company and the
Warrant Agent may by supplemental agreement make any changes or corrections in
the Agreement that they may deem necessary or desirable and which do not
adversely affect the interests of the holders of Warrant Certificates.

                                   AGREEMENTS

          In consideration of the foregoing and the mutual covenants and
agreements contained herein and in the Agreement, and intending to be legally
bound hereby, the Warrant Agent and the Company hereby agree as follows:

          1. Amendment of Section 1(i). The definition of "Warrant Expiration
Date" in Section 1(i) of the Agreement is hereby amended to read in its entirety
as follows:

               "Warrant Expiration Date" shall mean 5 p.m. (Central Time) on
               October 21, 2001, or if such date shall in the State of Wisconsin
               be a holiday or a day on which banks are authorized to close,
               then 5 p.m. (Central Time) on the next

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               following day which in the State of Wisconsin is not a holiday or
               a day on which banks are authorized to close. Unless exercised
               during the Warrant Exercise Period, the Warrants will
               automatically expire. The Warrants may be called for redemption
               and the expiration date herefor accelerated, on the terms and
               conditions set forth in sections 4(b) and 4(c) of this Agreement.
               If so called for redemption, Warrant Certificate holders shall
               have a period of at least 30 days after the date of the call
               notice within which to exercise the Warrants. However, Warrant
               Certificate holders will receive the redemption price only if
               such certificates are surrendered to the Corporate Office within
               the redemption period (as defined below).

          2. Full Force and Effect. All remaining provisions of the Agreement,
as previously amended, remain unchanged and in full force and effect.

          3. Governing Law. This Amendment shall be governed by and construed in
accordance with the laws of the State of Wisconsin. Section headings in this
Amendment appear for convenience of reference only and shall not be used in any
interpretation of this Amendment.

          4. Binding Effect. This Amendment shall be binding upon and inure to
the benefit of the Company, the Warrant Agent and their respective successors
and assigns, and the Registered Holders from time to time of Warrant
Certificates or any of them. Nothing in this Amendment shall be construed to
confer any right, remedy or claim upon any other person.

          5. Counterparts. This Amendment may be executed in counterparts, which
taken together shall constitute a single document.

     IN WITNESS WHEREOF, the Warrant Agent and the Company have caused this
Amendment to be executed as of the date first written above by their respective
officers thereunto duly authorized.

                                           MURDOCK COMMUNICATIONS CORPORATION


                                           BY /s/ Paul C. Tunink
                                              ----------------------------------
                                                  Paul C. Tunink, Vice President


                                           FIRSTAR BANK, N.A.


                                           BY /s/
                                              ----------------------------------
                                                  Authorized Officer

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