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                                                                     Exhibit 8.1


                                 April 6, 1998


Parker-Hannifin Corporation
6035 Parkland Boulevard
Cleveland, Ohio  44124


         Re:      Parker-Hannifin Corporation Medium-Term Notes


Ladies and Gentlemen:

         We have acted as special tax counsel to Parker-Hannifin Corporation
(the "Company") in connection with its medium-term notes (the "Notes"), which
may be issued in one or more series and may be offered and sold in the United
States from time to time, as set forth in the Company's Prospectus (the
"Prospectus"), dated March 23, 1998, and the Company's Prospectus Supplement
(the "Prospectus Supplement"), dated April 6, 1998.

         This letter will be deemed accepted by you in the form hereof upon the
filing of the Prospectus Supplement with the Securities and Exchange Commission.
Your acceptance of this letter in the form hereof constitutes your acceptance
of, and acquiescence in, the assumptions, exclusions, limitations and rules of
construction set forth below.


1.   AUTHORITIES EXAMINED

         In rendering the opinion set forth below, we have examined and relied
upon provisions of the Internal Revenue Code of 1986, as amended (hereinafter
"I.R.C." or the "Code"); final, temporary and proposed regulations promulgated
under the Code by the U.S. Department of the Treasury; administrative
pronouncements issued by the U.S. Internal Revenue Service; judicial decisions
rendered by U.S. Federal courts of competent jurisdiction; and such other




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sources and authorities that we have deemed relevant in reaching the conclusions
expressed herein.

2.   OPINION

         Based upon the foregoing, and subject to the assumptions, exclusions
and limitations set forth below, we are of the opinion that the discussion
contained in the section of the Prospectus Supplement entitled "United States
Taxation" accurately reflects the material United States federal income tax
consequences of the ownership and disposition of the Notes purchased by an
initial Holder (as defined in such section) thereof at the "issue price" (as
defined in such section).


3.   ASSUMPTIONS

         In rendering the opinion set forth above, we have assumed (and we have
made no independent investigation or inquiry whatsoever to confirm, and we
expressly disclaim any intent, undertaking or obligation to make any such
investigation or inquiry to confirm) that:

         3.1.     Each document that was required to be executed but was not
                  executed, or that was otherwise not in final form, on the date
                  on which we examined such document, will be timely executed
                  and/or delivered in final form, which final form will not
                  differ in any material respect from the form in which such
                  document was examined by us on such date.

         3.2.     The representations made to us by officers of the Company,
                  whether orally or in writing, with respect to the subject
                  matter of the opinion set forth above are true, correct and
                  complete in all material respects as of the date they were
                  made and at all times thereafter through and including the
                  date hereof.

         3.3.     The transactions contemplated by the Prospectus Supplement
                  will not contravene any obligation to which any party is
                  subject.

         3.4.     All assumptions made in connection with the delivery of any
                  other opinion to the addressee hereof or any other person,
                  whether by ourselves or by any other


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                  professional adviser, in connection with any transaction or
                  subject matter reasonably related to the subject matter of our
                  opinion set forth above are correct at all relevant times
                  through and including the later of the date of such other
                  opinion and the date hereof.

4.   EXCLUSIONS

         Anything in the foregoing to the contrary notwithstanding, we expressly
decline to opine upon, and expressly disclaim any intent, undertaking or
obligation to opine upon, and hereby expressly exclude from the scope of the
opinion set forth above, the following matters:

         4.1.     Any and all matters arising under the laws of any State of the
                  United States or the District of Columbia or any political
                  subdivision thereof.

         4.2.     Any and all matters arising under the laws of any country
                  other than the United States. For this purpose, the
                  dependencies, protectorates, territories and possessions of
                  the United States shall be deemed to be countries other than
                  the United States.

         4.3.     Any and all matters with respect to any tax other than the
                  U.S. Federal income tax.

         4.4.     The effect upon the opinion set forth above of any provision
                  of law that may affect any particular person differently from
                  any other person, by reason of such first-mentioned person's
                  special status, characteristics or situation.


5.   LIMITATIONS

         5.1.     The opinion set forth above is furnished only as to facts and
                  circumstances existing at the date hereof and actually known
                  or represented to us on such date. If any such facts and
                  circumstances should change, or if a determination is made
                  hereafter that any such facts or circumstances were untrue or
                  inaccurate on such date, any such change or determination
                  could adversely affect or render inappli-


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                  cable the opinion set forth above. We expressly disclaim any
                  intent, undertaking or obligation to notify the addressee
                  hereof or any other person of any such change or determination
                  of which we may subsequently become aware or any possible
                  effects thereof on the opinion set forth above.

         5.2.     The opinion set forth above is furnished in express reliance
                  on the assumptions set forth in Section 3 hereof. If a
                  determination is made hereafter that any such assumption was
                  untrue or inaccurate as of the date hereof, any such
                  determination could adversely affect or render inapplicable
                  the opinion set forth above. We expressly disclaim any intent,
                  undertaking or obligation to notify the addressee hereof or
                  any other person of any such determination of which we may
                  subsequently become aware or of any possible effects thereof
                  on the opinion set forth above.

         5.3.     Each of the sources and authorities described in Section 1
                  hereof is subject to repeal, revocation or modification
                  without notice, possibly with retroactive effect; any such
                  repeal, revocation or modification could adversely affect or
                  render inapplicable the opinion set forth above. The opinion
                  set forth above applies only to the subject matter thereof as
                  at the date hereof, and we expressly disclaim any intent,
                  undertaking or obligation to notify the addressee hereof or
                  any other person of any such repeal, revocation or
                  modification or any possible effects thereof on the opinion
                  set forth above.

         5.4.     The contents of Section 2 hereof, subject to and as modified
                  by the remaining contents hereof, constitute the entirety of
                  the opinion and advice furnished by us to the addressee hereof
                  with respect to the subject matter hereof. This original and
                  any simultaneously executed counterparts hereof together
                  constitute one and the same original writing, which writing
                  supersedes any and all (a) prior drafts or versions hereof and
                  (b) prior or contemporaneous statements, conclusions,
                  representations, writings, understandings, opinions,
                  discussions and other


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                  communications in any form between us and any addressee hereof
                  relating to the subject matter hereof. In proving the
                  existence or contents of this letter, it shall not be
                  necessary to produce, refer to or account for (a) any
                  particular executed original counterpart hereof in preference
                  to any other such counterpart, or (b) more than one such
                  counterpart.

         5.5.     No oral communication made after the date hereof shall be
                  deemed or effective to modify the contents hereof in any
                  manner. No written communication made after the date hereof
                  shall be deemed or effective to modify the contents hereof in
                  any manner, except to the extent that any such modification is
                  explicitly set forth in such subsequent written communication
                  and contains an express reference to this letter.

         5.6.     In rendering the opinion contained in Section 2 hereof, we do
                  not purport to be experts on laws other than the Federal laws
                  of the United States.

         5.7.     The opinion set forth above is furnished solely for the
                  benefit of the addressee hereof and may not, except as
                  specifically provided below, be used, relied upon, referred to
                  or quoted by any other person without our prior specific
                  written consent thereto. There are no express or implied
                  third-party beneficiaries of or in the opinion set forth
                  above.


6.   RULES OF CONSTRUCTION

         In interpreting the provisions of this letter, the following rules of 
interpretation and construction shall apply:


         6.1.     The terms and provisions hereof and the wording used herein
                  shall in all cases be interpreted and construed in accordance
                  with their fair meanings and not strictly for or against any
                  person.




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         6.2.     Capitalized terms used herein without definition have the
                  respective meanings set forth in the Prospectus or Prospectus
                  Supplement.

         6.3.     The captions at the headings of each Section of this letter
                  are provided for convenience of reference only, and are in no
                  way intended or to be used or applied to describe, interpret,
                  construe, define or limit the scope, extent, intent, meaning
                  or operation of any term or provision hereof.

         6.4.     Unless the context clearly requires otherwise, each reference
                  to, and each use of, any of the masculine, feminine or neuter
                  genders herein shall be deemed to constitute a reference to,
                  and a use of, each such gender without distinction.

         6.5.     Unless the context clearly requires otherwise, each reference
                  to, and each use of, either the singular or plural number
                  herein shall be deemed to constitute a reference to, and a use
                  of, each such number without distinction.

                                      ****

         We hereby consent to the furnishing of the opinion as Exhibit 8.1 to
Registration Statement No. 333-47955 on Form 8-3 filed by the Company to effect
registration of the Notes under the Securities Act of 1933 and to the reference
to us under the caption "United States Taxation" in the Prospectus Supplement.


                                        Very truly yours,


                                        Jones, Day, Reavis & Pogue