As filed with the Securities and Exchange Commission on March 22, 1999.
                                                         Registration No. 333-
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                         ------------------------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                         ------------------------------


 Incorporated              MERIDIAN DIAGNOSTICS, INC.          I.R.S. Employer
Under the Laws               3471 RIVER HILLS DRIVE           Identification No.
 of Ohio                     CINCINNATI, OHIO 45244              31-0888197
                                (513) 271-3700


                        1999 DIRECTORS' STOCK OPTION PLAN
                                       and
                             1996 STOCK OPTION PLAN
                 AMENDED AND RESTATED EFFECTIVE JANUARY 22, 1999

                         ------------------------------

                             Robert E. Coletti, Esq.
                       Keating, Muething & Klekamp, P.L.L.
                             One East Fourth Street
                             Cincinnati, Ohio 45202
                                 (513) 579-6411
                         ------------------------------
                         (Agent for Service of Process)


                         CALCULATION OF REGISTRATION FEE
--------------------------------------------------------------------------------
                                     Proposed       Proposed
                                      Maximum        Maximum
    Title of          Amount         Offering       Aggregate        Amount of
   Securities          To Be           Price        Offering       Registration
To Be Registered   Registered(1)   Per Share(2)     Price(2)          Fee(3)
--------------------------------------------------------------------------------
  Common Stock,       550,000         $5.9375      $3,265,625.00        $907.84
  No par value        Shares
--------------------------------------------------------------------------------

(1)  This  Registration  Statement is filed for up to 50,000  shares and 500,000
     shares,  respectively,  issuable  upon  the  exercise  of  options  granted
     pursuant to the 1999 Directors' Stock Option Plan and the 1996 Stock Option
     Plan Amended and Restated Effective January 22, 1999.

(2)  Estimated to calculate registration fee.

(3)  Calculated pursuant to Rule 457(h) based on the average of the high and low
     prices of the Common  Stock on the Nasdaq Stock Market on March 15, 1999 of
     $5.9375 per share.


<PAGE>


                                      - 2 -


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

     The  following  documents  filed by Meridian  Diagnostics,  Inc.,  with the
Securities and Exchange Commission are incorporated herein by reference and made
a part hereof:


     1.   The  Company's  Annual Report on Form 10-K,  including all  amendments
          thereto, for the Fiscal Year ended September 30, 1998.

     2.   The Company's Form 8-K filed on November 13, 1998 and Form 8-K/A filed
          on January 19, 1999.

     3.   The Company's Form 10-Q for the quarter ended December 31, 1998.

     4.   The  description  of  the  Company's  Common  Stock  contained  in the
          Registration  Statement  on Form 8-A  filed  on  August  15,  1986 and
          amended August 20, 1986 under the Securities Act of 1934.

     All reports and other documents  subsequently filed by the Company pursuant
to Sections 13(a),  13(c), 14 and 15(d) of the Securities  Exchange Act of 1934,
prior to the  filing of a  post-effective  amendment  which  indicates  that all
Common Stock  offered has been sold or which  deregisters  all Common Stock then
remaining  unsold,  shall be  deemed to be  incorporated  by  reference  in this
Registration  Statement  and to be a part  hereof  from the date of filing  such
documents.

Item 4. Description of Securities

     Not Applicable.


Item 5. Interests of Named Experts and Counsel

     The legality of the Common Stock offered hereby will be passed upon for the
Company by Keating,  Muething & Klekamp,  P.L.L., 1400 Provident Tower, One East
Fourth Street, Cincinnati, Ohio 45202. Attorneys of Keating, Muething & Klekamp,
P.L.L. own approximately 52,336 shares of the Company's Common Stock.


<PAGE>


                                      - 3 -



Item 6. Indemnification of Directors and Officers

     Ohio  Revised  Code,  Section  1701.13(E),  allows  indemnification  by the
registrant  to  any  person  made  or  threatened  to be  made  a  party  to any
proceedings,  other than a proceeding by or in the right of the  registrant,  by
reason of the fact that he is or was a director,  officer,  employee or agent of
the registrant,  against expenses,  including judgment and fines, if he acted in
good faith and in a manner  reasonably  believed  to be in or not opposed to the
best interests of the registrant and, with respect to criminal actions, in which
he had no  reasonable  cause to believe that his conduct was  unlawful.  Similar
provisions apply to actions brought by or in the right of the registrant, except
that no  indemnification  shall be made in such cases when the person shall have
been adjudged to be liable for negligence or misconduct to the registrant unless
deemed otherwise by the court.  Indemnification is to be made by a majority vote
of a quorum of  disinterested  directors or the written  opinion of  independent
counsel  or by the  shareholders  or by the  court.  The  registrant's  Code  of
Regulations extends such indemnification.

Item 7. Exemption from Registration Claimed

     Not Applicable.

Item 8. Exhibits*


  Exhibit 4.1    Meridian Diagnostics, Inc. 1999 Directors' Stock Option Plan
                 (incorporated by reference to the Company's Form Def 14A filed
                 December 21, 1998)
  Exhibit 4.2    Meridian Diagnostics, Inc. 1996 Stock Option Plan Amended and
                 Restated Effective January 22, 1999 (incorporated by reference
                 to the Company's Form Def 14A filed December 21, 1998)
  Exhibit 5      Opinion of Keating, Muething & Klekamp, P.L.L.
  Exhibit 23.1   Consent of Arthur Andersen LLP
  Exhibit 23.2   Consent of Keating, Muething & Klekamp, P.L.L. (included in
                 Exhibit 5)
  Exhibit 24     Power of Attorney (contained on the signature page)


--------

     *All Exhibits filed herewith.


<PAGE>


                                      - 4 -


Item 9. Undertakings

     9.1 The undersigned  registrant hereby undertakes to file during any period
in which  offers or sales are being made,  a  post-effective  amendment  to this
Registration  Statement:(i)  to  include  any  prospectus  required  by  Section
10(a)(3) of the  Securities  Act of 1933;  (ii) to reflect in the prospectus any
facts or events arising after the effective date of this Registration  Statement
(or the most recent post-effective amendment thereof) which,  individually or in
the aggregate,  represent a fundamental  change in the  information set forth in
this  Registration  Statement.  Notwithstanding  the foregoing,  any increase or
decrease  in  volume  of  securities  offered  (if the  total  dollar  value  of
securities offered would not exceed that which was registered) and any deviation
from  the  low or  high  end of the  estimated  maximum  offering  range  may be
reflected in the form of prospectus  filed with the Commission  pursuant to Rule
424(b) if, in the aggregate,  the changes in volume and price  represent no more
than a 20%  change  in the  maximum  aggregate  offering  price set forth in the
"Calculation of Registration Fee" table in the effective Registration Statement;
(iii)  to  include  any  material  information  with  respect  to  the  plan  of
distribution  not  previously  disclosed  in the  Registration  Statement or any
material change to such  information in the  Registration  Statement;  provided,
however,  that (i) and (ii) above do not apply if the information required to be
included in a  post-effective  amendment  by those  paragraphs  is  contained in
periodic  reports filed with or furnished to the  Commission  by the  registrant
pursuant to Section 13 or Section 15(d) of the  Securities  Exchange Act of 1934
that are incorporated by reference in the Registration Statement.

     9.2 The undersigned  registrant  hereby undertakes that, for the purpose of
determining   any  liability  under  the  Securities  Act  of  1933,  each  such
post-effective  amendment  shall be  deemed to be a new  registration  statement
relating to the securities offered therein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

     9.3  The   undersigned   registrant   hereby   undertakes  to  remove  from
registration by means of a post-effective  amendment any of the securities being
registered which remain unsold at the termination of the offering.

     9.4 The  undersigned  registrant  hereby  undertakes  that, for purposes of
determining  any liability  under the Securities Act of 1933, each filing of the
registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Securities  Exchange  Act of 1934  (and,  where  applicable,  each  filing of an
employee  benefit  plan's  annual  report  pursuant  to  Section  15(d)  of  the
Securities  Exchange  Act of 1934)  that is  incorporated  by  reference  in the
Registration  Statement  shall  be  deemed  to be a new  registration  statement
relating to the securities offered therein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

     9.5 Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the  registrant  pursuant  to  the  foregoing  provisions,   or  otherwise,  the
registrant  has been advised that in the opinion of the  Securities and Exchange
Commission such indemnification is against public policy as expressed in the Act



<PAGE>


                                      - 5 -


and is, therefore,  unenforceable. In the event that a claim for indemnification
against such  liabilities  (other than the payment by the registrant of expenses
incurred or paid by a director,  officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director,  officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been  settled by  controlling  precedent,  submit to a court of  appropriate
jurisdiction the question whether such  indemnification  by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                   SIGNATURES

     Pursuant to the  requirements of the Securities Act of 1933, the registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in Cincinnati, Ohio, on March 22, 1999.

                                     MERIDIAN DIAGNOSTICS, INC.


                                     By: /s/ William J. Motto
                                         ----------------------------
                                           William J. Motto
                                           Chairman of the Board and
                                           Chief Executive Officer

     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has  been  signed  by  the  following  persons  in  the
capacities  and on the dates  indicated.  Persons whose names are marked with an
asterisk  (*) below hereby  designate  William J. Motto or Gerard Blain as their
attorney-in-fact   to  sign  all   amendments,   including  any   post-effective
amendments, to this Registration Statement.


       Signature                        Capacity                      Date
       ---------                        --------                      ----


*/s/ William J. Motto
--------------------------    Chairman of the Board and Chief     March 22, 1999
William J. Motto              Executive Officer (Principal
                              Executive Officer)


*/s/ John A. Kraeutler
--------------------------    President, Chief Operating          March 22, 1999
John A. Kraeutler             Officer and Director



<PAGE>


                               - 6 -




*
--------------------------    Executive Vice President,           March 22, 1999
Gerard Blain                  Chief Financial Officer


*
--------------------------    Director                            March 22, 1999
James A. Buzard


/s/ Gary P. Kreider
--------------------------    Director                            March 22, 1999
Gary P. Kreider


*/s/ Robert J. Ready
--------------------------    Director                            March 22, 1999
Robert J. Ready


*
--------------------------    Director                            March 22, 1999
Jerry L. Ruyan
[{"type": "S-8", "sequence": "1", "description": "FORM S-8 FOR MERIDIAN DIAGNOSTICS, INC.", "secsgml_size_bytes": 13816}]
{"company-data": {"conformed-name": "MERIDIAN DIAGNOSTICS INC", "cik": "0000794172", "assigned-sic": "2835", "irs-number": "310888197", "state-of-incorporation": "OH", "fiscal-year-end": "0930"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-74825", "film-number": "99570102"}, "business-address": {"street1": "3471 RIVER HILLS DR", "city": "CINCINNATI", "state": "OH", "zip": "45244", "phone": "5132713700"}, "mail-address": {"street1": "3471 RIVER HILLS DRIVE", "city": "CINCINNATI", "state": "OH", "zip": "45244"}}
As filed with the Securities and Exchange Commission on March 22, 1999.
                                                         Registration No. 333-
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                         ------------------------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                         ------------------------------

 Incorporated              MERIDIAN DIAGNOSTICS, INC.          I.R.S. Employer
Under the Laws               3471 RIVER HILLS DRIVE           Identification No.
 of Ohio                     CINCINNATI, OHIO 45244              31-0888197
                                (513) 271-3700

                        1999 DIRECTORS' STOCK OPTION PLAN
                                       and
                             1996 STOCK OPTION PLAN
                 AMENDED AND RESTATED EFFECTIVE JANUARY 22, 1999

                         ------------------------------

                             Robert E. Coletti, Esq.
                       Keating, Muething & Klekamp, P.L.L.
                             One East Fourth Street
                             Cincinnati, Ohio 45202
                                 (513) 579-6411
                         ------------------------------
                         (Agent for Service of Process)

                         CALCULATION OF REGISTRATION FEE
--------------------------------------------------------------------------------
                                     Proposed       Proposed
                                      Maximum        Maximum
    Title of          Amount         Offering       Aggregate        Amount of
   Securities          To Be           Price        Offering       Registration
To Be Registered   Registered(1)   Per Share(2)     Price(2)          Fee(3)
--------------------------------------------------------------------------------
  Common Stock,       550,000         $5.9375      $3,265,625.00        $907.84
  No par value        Shares
--------------------------------------------------------------------------------

(1)  This  Registration  Statement is filed for up to 50,000  shares and 500,000
     shares,  respectively,  issuable  upon  the  exercise  of  options  granted
     pursuant to the 1999 Directors' Stock Option Plan and the 1996 Stock Option
     Plan Amended and Restated Effective January 22, 1999.

(2)  Estimated to calculate registration fee.

(3)  Calculated pursuant to Rule 457(h) based on the average of the high and low
     prices of the Common  Stock on the Nasdaq Stock Market on March 15, 1999 of
     $5.9375 per share.
- 2 -

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

     The  following  documents  filed by Meridian  Diagnostics,  Inc.,  with the
Securities and Exchange Commission are incorporated herein by reference and made
a part hereof:

     1.   The  Company's  Annual Report on Form 10-K,  including all  amendments
          thereto, for the Fiscal Year ended September 30, 1998.

     2.   The Company's Form 8-K filed on November 13, 1998 and Form 8-K/A filed
          on January 19, 1999.

     3.   The Company's Form 10-Q for the quarter ended December 31, 1998.

     4.   The  description  of  the  Company's  Common  Stock  contained  in the
          Registration  Statement  on Form 8-A  filed  on  August  15,  1986 and
          amended August 20, 1986 under the Securities Act of 1934.

     All reports and other documents  subsequently filed by the Company pursuant
to Sections 13(a),  13(c), 14 and 15(d) of the Securities  Exchange Act of 1934,
prior to the  filing of a  post-effective  amendment  which  indicates  that all
Common Stock  offered has been sold or which  deregisters  all Common Stock then
remaining  unsold,  shall be  deemed to be  incorporated  by  reference  in this
Registration  Statement  and to be a part  hereof  from the date of filing  such
documents.

Item 4. Description of Securities

     Not Applicable.

Item 5. Interests of Named Experts and Counsel

     The legality of the Common Stock offered hereby will be passed upon for the
Company by Keating,  Muething & Klekamp,  P.L.L., 1400 Provident Tower, One East
Fourth Street, Cincinnati, Ohio 45202. Attorneys of Keating, Muething & Klekamp,
P.L.L. own approximately 52,336 shares of the Company's Common Stock.
- 3 -

Item 6. Indemnification of Directors and Officers

     Ohio  Revised  Code,  Section  1701.13(E),  allows  indemnification  by the
registrant  to  any  person  made  or  threatened  to be  made  a  party  to any
proceedings,  other than a proceeding by or in the right of the  registrant,  by
reason of the fact that he is or was a director,  officer,  employee or agent of
the registrant,  against expenses,  including judgment and fines, if he acted in
good faith and in a manner  reasonably  believed  to be in or not opposed to the
best interests of the registrant and, with respect to criminal actions, in which
he had no  reasonable  cause to believe that his conduct was  unlawful.  Similar
provisions apply to actions brought by or in the right of the registrant, except
that no  indemnification  shall be made in such cases when the person shall have
been adjudged to be liable for negligence or misconduct to the registrant unless
deemed otherwise by the court.  Indemnification is to be made by a majority vote
of a quorum of  disinterested  directors or the written  opinion of  independent
counsel  or by the  shareholders  or by the  court.  The  registrant's  Code  of
Regulations extends such indemnification.

Item 7. Exemption from Registration Claimed

     Not Applicable.

Item 8. Exhibits*

  Exhibit 4.1    Meridian Diagnostics, Inc. 1999 Directors' Stock Option Plan
                 (incorporated by reference to the Company's Form Def 14A filed
                 December 21, 1998)
  Exhibit 4.2    Meridian Diagnostics, Inc. 1996 Stock Option Plan Amended and
                 Restated Effective January 22, 1999 (incorporated by reference
                 to the Company's Form Def 14A filed December 21, 1998)
  Exhibit 5      Opinion of Keating, Muething & Klekamp, P.L.L.
  Exhibit 23.1   Consent of Arthur Andersen LLP
  Exhibit 23.2   Consent of Keating, Muething & Klekamp, P.L.L. (included in
                 Exhibit 5)
  Exhibit 24     Power of Attorney (contained on the signature page)

--------

     *All Exhibits filed herewith.
- 4 -

Item 9. Undertakings

     9.1 The undersigned  registrant hereby undertakes to file during any period
in which  offers or sales are being made,  a  post-effective  amendment  to this
Registration  Statement:(i)  to  include  any  prospectus  required  by  Section
10(a)(3) of the  Securities  Act of 1933;  (ii) to reflect in the prospectus any
facts or events arising after the effective date of this Registration  Statement
(or the most recent post-effective amendment thereof) which,  individually or in
the aggregate,  represent a fundamental  change in the  information set forth in
this  Registration  Statement.  Notwithstanding  the foregoing,  any increase or
decrease  in  volume  of  securities  offered  (if the  total  dollar  value  of
securities offered would not exceed that which was registered) and any deviation
from  the  low or  high  end of the  estimated  maximum  offering  range  may be
reflected in the form of prospectus  filed with the Commission  pursuant to Rule
424(b) if, in the aggregate,  the changes in volume and price  represent no more
than a 20%  change  in the  maximum  aggregate  offering  price set forth in the
"Calculation of Registration Fee" table in the effective Registration Statement;
(iii)  to  include  any  material  information  with  respect  to  the  plan  of
distribution  not  previously  disclosed  in the  Registration  Statement or any
material change to such  information in the  Registration  Statement;  provided,
however,  that (i) and (ii) above do not apply if the information required to be
included in a  post-effective  amendment  by those  paragraphs  is  contained in
periodic  reports filed with or furnished to the  Commission  by the  registrant
pursuant to Section 13 or Section 15(d) of the  Securities  Exchange Act of 1934
that are incorporated by reference in the Registration Statement.

     9.2 The undersigned  registrant  hereby undertakes that, for the purpose of
determining   any  liability  under  the  Securities  Act  of  1933,  each  such
post-effective  amendment  shall be  deemed to be a new  registration  statement
relating to the securities offered therein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

     9.3  The   undersigned   registrant   hereby   undertakes  to  remove  from
registration by means of a post-effective  amendment any of the securities being
registered which remain unsold at the termination of the offering.

     9.4 The  undersigned  registrant  hereby  undertakes  that, for purposes of
determining  any liability  under the Securities Act of 1933, each filing of the
registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Securities  Exchange  Act of 1934  (and,  where  applicable,  each  filing of an
employee  benefit  plan's  annual  report  pursuant  to  Section  15(d)  of  the
Securities  Exchange  Act of 1934)  that is  incorporated  by  reference  in the
Registration  Statement  shall  be  deemed  to be a new  registration  statement
relating to the securities offered therein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

     9.5 Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the  registrant  pursuant  to  the  foregoing  provisions,   or  otherwise,  the
registrant  has been advised that in the opinion of the  Securities and Exchange
Commission such indemnification is against public policy as expressed in the Act
- 5 -

and is, therefore,  unenforceable. In the event that a claim for indemnification
against such  liabilities  (other than the payment by the registrant of expenses
incurred or paid by a director,  officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director,  officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been  settled by  controlling  precedent,  submit to a court of  appropriate
jurisdiction the question whether such  indemnification  by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                   SIGNATURES

     Pursuant to the  requirements of the Securities Act of 1933, the registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in Cincinnati, Ohio, on March 22, 1999.

                                     MERIDIAN DIAGNOSTICS, INC.

                                     By: /s/ William J. Motto
                                         ----------------------------
                                           William J. Motto
                                           Chairman of the Board and
                                           Chief Executive Officer

     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has  been  signed  by  the  following  persons  in  the
capacities  and on the dates  indicated.  Persons whose names are marked with an
asterisk  (*) below hereby  designate  William J. Motto or Gerard Blain as their
attorney-in-fact   to  sign  all   amendments,   including  any   post-effective
amendments, to this Registration Statement.

       Signature                        Capacity                      Date
       ---------                        --------                      ----

*/s/ William J. Motto
--------------------------    Chairman of the Board and Chief     March 22, 1999
William J. Motto              Executive Officer (Principal
                              Executive Officer)

*/s/ John A. Kraeutler
--------------------------    President, Chief Operating          March 22, 1999
John A. Kraeutler             Officer and Director
- 6 -

*
--------------------------    Executive Vice President,           March 22, 1999
Gerard Blain                  Chief Financial Officer

*
--------------------------    Director                            March 22, 1999
James A. Buzard

/s/ Gary P. Kreider
--------------------------    Director                            March 22, 1999
Gary P. Kreider

*/s/ Robert J. Ready
--------------------------    Director                            March 22, 1999
Robert J. Ready

*
--------------------------    Director                            March 22, 1999
Jerry L. Ruyan