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                  [LETTERHEAD OF KEATING, MUETHING & KLEKAMP]

                            FACSIMILE (513) 579-6956


                                  May 14, 1996



Direct Dial:  (513) 579-6468



                                                                       EXHIBIT 5
Meridian Diagnostics, Inc.
3471 River Hills Drive
Cincinnati, Ohio  45246

Gentlemen:

         We have examined the corporate records and proceedings of Meridian
Diagnostics, Inc. (the "Corporation") with respect to:

         1.       The organization of the Corporation; and

         2.       The legal sufficiency of all corporate proceedings of the
Corporation in connection with the creation and issuance of all of the present
outstanding and issued shares of Common Stock, no par value, of the Corporation
(the "Common Stock").

         Based upon such examination, we are of the opinion:

         1.       That the Corporation is a duly organized and validly existing
corporation in good standing under the laws of the State of Ohio; and

         2.       That the 100,000 shares of Common Stock, plus up to 15,000
which may be sold pursuant to an over-allotment option, all of which are being
sold by the selling shareholder are duly authorized, legally issued, fully paid
and non-assessable shares of Common Stock free of any claim of pre-emptive
rights.


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        We hereby consent to be named in the Registration Statement and the
Prospectus part thereof as the attorneys who will pass upon legal matters in
connection with the aforesaid shares of Common Stock and to the filing of this
opinion as an exhibit to the Registration Statement, and furthermore consent to
all references made to this firm in the Registration Statement.

                                           Yours truly,

                                           KEATING, MUETHING & KLEKAMP



                                           BY:     /s/ Edward E. Steiner
                                               --------------------------
                                                   Edward E. Steiner


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