Exhibit 5.1
 








                                                  March 13, 1998




Parker-Hannifin Corporation
6035 Parkland Boulevard
Cleveland, Ohio   44124-4141

         Re:      $600,000,000 Aggregate Amount of Senior Debt
                  Securities of Parker-Hannifin Corporation
                  -----------------------------------------

Gentlemen:

                  We are acting as counsel for Parker-Hannifin Corporation, an
Ohio corporation (the "Company"), in connection with the creation and
authorization of the issuance and sale of up to $600,000,000 aggregate amount of
Senior Debt Securities (the "Securities"), to be issued pursuant to an
Indenture, dated as of May 3, 1996 (the "Indenture"), entered into between the
Company and National City Bank, as Trustee (the "Trustee").

                  We have examined such documents, records and matters of law as
we have deemed necessary for purposes of this opinion, and based thereupon, but
subject to the assumptions and qualifications set forth below, we are of the
opinion that:

                  1. The Indenture constitutes a valid and binding instrument of
the Company.

                  2. The Securities have been duly authorized and, when duly
executed, authenticated and delivered to and paid for by the purchasers thereof
in accordance with the terms of such Securities, the Indenture and the U.S.     
Distribution Agreement, will be valid and binding obligations of the Company
and will be entitled to the benefits of the Indenture.

                  In rendering the foregoing opinions we have also assumed that
the U.S. Distribution Agreement will be executed and delivered by the Company
and the Agents in





Parker-Hannifin Corporation
March 13, 1998
Page 2





substantially the form filed as Exhibit 1.1 to the Registration Statement on
Form S-3 filed by the Company to effect registration of the Securities under the
Securities Act of 1933 (the "Registration Statement").

                  We hereby consent to the filing of this opinion as Exhibit 5.1
to the Registration Statement and to the reference to us under the caption
"Legal Matters" in the Prospectus constituting a part of such Registration
Statement.

                                        Very truly yours,


                                        Jones, Day, Reavis & Pogue