Exhibit(a)(4)

                 LETTER TO BROKERS, DEALERS, COMMERCIAL BANKS,
                       TRUST COMPANIES AND OTHER NOMINEES

                           MERIDIAN BIOSCIENCE, INC.

                               OFFER TO EXCHANGE
                5% CONVERTIBLE SUBORDINATED DEBENTURES DUE 2013
             IN PRINCIPAL AMOUNT OF $16,000,000 FOR EQUAL AMOUNT OF
          OUTSTANDING 7% CONVERTIBLE SUBORDINATED DEBENTURES DUE 2006
                      PURSUANT TO THE OFFERING MEMORANDUM,

                            DATED NOVEMBER 12, 2003

        THE EXCHANGE OFFER WILL EXPIRE AT 12:00 MIDNIGHT, EASTERN TIME,
          ON DECEMBER 11, 2003, UNLESS EXTENDED OR EARLIER TERMINATED.

                               November 12, 2003

To: Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees:

     Meridian Bioscience, Inc. is offering to exchange (the "Exchange Offer"),
upon and subject to the terms and conditions set forth in the Offering
Memorandum, dated November 12, 2003 (the "Offering Memorandum"), and the
enclosed Letter of Transmittal (the "Letter of Transmittal"), its 5% Convertible
Subordinated Debentures due 2013 in the principal amount of $16,000,000 for an
equal principal amount of its outstanding 7% Convertible Subordinated Debentures
due 2006 (the "Existing Debentures").

     We are requesting that you contact your clients for whom you hold Existing
Debentures regarding the Exchange Offer. For your information and for forwarding
to your clients for whom you hold Existing Debentures registered in your name or
in the name of your nominee, or who hold Existing Debentures registered in their
own names, we are enclosing the following documents:

     1. Offering Memorandum, dated November 12, 2003;

     2. The Letter of Transmittal for your use and for the information of your
        clients;

     3. A Notice of Guaranteed Delivery to be used to accept the Exchange Offer
        if certificates for the Existing Debentures are not immediately
        available, time will not permit all required documents to reach the
        Exchange Agent prior to the Expiration Date (as defined below), or the
        procedure for book-entry transfer cannot be completed on a timely basis;

     4. A form of letter which may be sent to your clients for whose account you
        hold Existing Debentures registered in your name or the name of your
        nominee, with space provided for obtaining such clients' instructions
        with respect to the Exchange Offer; and

     5. Guidelines for Certification of Taxpayer Identification Number on
        Substitute Form W-9.

     Your prompt action is requested. The Exchange Offer will expire at 12:00
midnight, Eastern time, on December 11, 2003, unless extended by us (as it may
be extended, the "Expiration Date"). The Existing Debentures tendered pursuant
to the Exchange Offer may be withdrawn at any time before the Expiration Date or
at any time after December 12, 2003 if we have not accepted the tendered
Existing Debentures for exchange by that date.


     Unless a holder of Existing Debentures complies with the procedures
described in the section of the Offering Memorandum entitled "The Exchange
Offer -- Guaranteed Delivery Procedures," the holder must do one of the
following on or prior to the Expiration Date to participate in the Exchange
Offer:

     - tender the Existing Debentures by sending the certificates for the
       Existing Debentures, in proper form for transfer, a properly completed
       and duly executed Letter of Transmittal, with any required signature
       guarantees, and all other documents required by the Letter of
       Transmittal, to the Exchange Agent, at the address set forth on the front
       cover page of the Letter of Transmittal; or

     - tender the Existing Debentures by using the book-entry procedures
       described in the section of the Offering Memorandum entitled "The
       Exchange Offer -- Book-Entry Transfer" and transmitting a properly
       completed and duly executed Letter of Transmittal, with any required
       signature guarantees, or an "agent's message" (defined below) instead of
       the Letter of Transmittal, to the Exchange Agent.

     In order for a book-entry transfer to constitute a valid tender of Existing
Debentures, the Exchange Agent must receive a confirmation of book-entry
transfer (a "Book-Entry Confirmation") of the Existing Debentures into the
Exchange Agent's account at The Depository Trust Company prior to the Expiration
Date. The term "agent's message" means a message, transmitted by The Depository
Trust Company and received by the Exchange Agent and forming a part of the
Book-Entry Confirmation, which states that The Depository Trust Company has
received an express acknowledgment from the tendering holder of Existing
Debentures that the holder has received and has agreed to be bound by the Letter
of Transmittal.

     If a registered holder of Existing Debentures wishes to tender the Existing
Debentures in the Exchange Offer, but the certificates for the Existing
Debentures are not immediately available, time will not permit the certificates
for the Existing Debentures or other required documents to reach the Exchange
Agent before the Expiration Date, or the procedure for book-entry transfer
cannot be completed before the Expiration Date, a tender of Existing Debentures
may be effected by following the Guaranteed Delivery Procedures described in the
section of the Offering Memorandum entitled "The Exchange Offer -- Guaranteed
Delivery Procedures."

     We will, upon request, reimburse brokers, dealers, commercial banks, trust
companies and other nominees for reasonable and necessary costs and expenses
incurred by them in forwarding the Offering Memorandum and the related documents
to the beneficial owners of Existing Debentures held by them as nominee or in a
fiduciary capacity. We will pay or cause to be paid all stock transfer taxes
applicable to the exchange of Existing Debentures in the Exchange Offer, except
as set forth in Instruction 13 of the Letter of Transmittal.

     Any inquiries you may have with respect to the Exchange Offer, or requests
for additional copies of the enclosed materials, should be directed to the
Exchange Agent for the Exchange Offer, at the telephone number or address set
forth on the front cover page of the Letter of Transmittal.

                           MERIDIAN BIOSCIENCE, INC.

     Nothing herein or in the enclosed documents shall constitute you or any
other person as an agent of Meridian Bioscience, Inc., the Exchange Agent or the
Information Agent, or authorize you or any other person to use any document or
make any statements on behalf of them with respect to the Exchange Offer, except
for statements expressly made in the Offering Memorandum or the Letter of
Transmittal.

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