[Letterhead of Reboul, MacMurray, Hewitt, Maynard & Kristol]

                                January 27, 2000





Concentra Operating Corporation
312 Union Wharf
Boston, Massachusetts 02109


                        Concentra Operating Corporation
                       Registration Statement on Form S-4
                           Registration No. 333-90765
                           --------------------------


Ladies and Gentlemen:

     We have acted as  counsel  to  Concentra  Operating  Corporation,  a Nevada
corporation  (the  "Company"),  in connection  with the  Company's  Registration
Statement on Form S-4 (the "Registration Statement"), filed under the Securities
Act of 1933,  as amended  (the  "Act"),  relating  to the  proposed offer by the
Company to exchange up to  $190,000,000  aggregate  principal  amount of its 13%
Senior  Subordinated  Notes due 2009,  Series B (the  "New  Notes"),  for a like
principal  amount of its  outstanding  13% Senior  Subordinated  Notes due 2009,
Series A (the "Old Notes").

     In that connection, we have examined originals, or copies certified or
otherwise identified to our satisfaction, of such documents, corporate records
and other instruments as we have deemeed necessary or appropriate for the
purposes of this opinion, including the Certificate of Incorporation an By-laws
of the Company.







                                       2



     Based upon the  foregoing,  we are of opinion  that the New Notes have been
duly and validly  authorized by the Company and, when issued under the Indenture
is substantially the form filed as Exhibit 4.1 to the Registration  Statement in
exchange  for the Old  Notes,  upon the  terms  and  subject  to the  conditions
contained in the Prospectus comprising part of the Registration Statement and in
the Letter of Transmittal substantially in the form filed as Exhibit 99.1 to the
Registration Statement, will be valid and binding obligations of the Company.

     We are  members of the bar of the State of New York and do not  express any
opinion  as to the law of any  jurisdiction  other than the laws of the State of
New York or the federal  laws of the United  States.  Our  opinions are rendered
only with respect to the laws, and the rules, regulations and orders thereunder,
which are currently in effect.

     We  hereby  consent  to the  use  of  this  opinion  as an  exhibit  to the
Registration Statement and to the reference to our firm under the caption "Legal
Matters" in the Prospectus comprising a part of the Registration  Statement.  By
giving the foregoing  consent,  we do not admit that we come within the category
of persons whose consent is required under Section 7 of the Act.


                                Very truly yours

                                /s/ Reboul, MacMurray, Hewitt, Maynard & Kristol
                                ------------------------------------------------
                                    Reboul, MacMurray, Hewitt, Maynard & Kristol