ASSIGNMENT AGREEMENT

                                       AND

                   SECOND AMENDMENT TO CONTRIBUTION AGREEMENT

     This Assignment  Agreement and Second  Amendment to Contribution  Agreement
(this "Agreement"),  dated as of April 1, 2000 (the "Effective Date"), is by and
between Prime Medical  Services,  Inc. a Delaware  corporation  ("PMSI"),  Prime
Medical Operating,  Inc., a Delaware  corporation  ("PMOI"),  Prime RVC, Inc., a
Delaware  corporation  ("Prime RVC"),  Prime  Refractive  Management,  L.L.C., a
Delaware  limited  liability  company ("Prime  Management"),  Barnet Dulaney Eye
Center,  P.L.L.C.,  an Arizona  professional limited liability company ("BDEC"),
LASIK  Investors,  L.L.C.,  a  Delaware  limited  liability  company  ("LASIK"),
Prime/BDR  Acquisition,  L.L.C.,  a Delaware limited  liability  company ("Prime
BDR"),  Prime/BDEC  Acquisition,  L.L.C., a Delaware limited  liability  company
("Prime BDEC"),  Prime Refractive,  L.L.C., a Delaware limited liability company
("Prime Refractive"), David D. Dulaney, M.D. ("Dulaney"), Ronald W. Barnet, M.D.
("Barnet"), and Mark Rosenberg ("Rosenberg"). All of the foregoing parties other
than Prime RVC are hereinafter referred to as the "Existing Parties".

                             Preliminary Statements

         LASIK  and  Prime  BDR are  each a party to that  certain  Contribution
Agreement,  dated as of September 1, 1999, among PMSI,  PMOI, Prime  Management,
BDEC,  LASIK,  Prime BDR, Prime BDEC, Prime  Refractive,  Dulaney,  Barnet,  and
Rosenberg,  as amended by that certain First Amendment to Contribution Agreement
dated as of January 31, 2000 (the "Contribution Agreement").

         The parties to this Agreement desire that LASIK transfer to PMOI all of
LASIK's  ownership in Prime BDR,  including,  without  limitation,  that certain
forty percent (40%) membership interest received by LASIK in connection with the
consummation of the transactions contemplated by the Contribution Agreement (the
"Prime BDR Interest").

         The parties to this Agreement desire that Prime Refractive  transfer to
Prime RVC all of Prime Refractive's  ownership in Caster One, L.L.C., a Delaware
limited  liability  company and partially owned  subsidiary of Prime  Refractive
("Caster One"), including,  without limitation, that certain sixty percent (60%)
membership  interest owned Prime Refractive  (collectively the "Caster Interest"
and, together with the Prime BDR Interest, the "Transferred Interests").

         In  partial   consideration   of  the  assignment  of  the  Transferred
Interests, PMSI desires to issue certain Warrants described herein.

         The Existing  Parties also desire that,  effective upon transfer of the
Transferred  Interests,  Prime RVC shall assume all  obligations for any and all
amounts  owed by  Prime  Refractive  to  Prime  Management  under  that  certain
Promissory  Note  executed  by Prime  Refractive  and dated March 1, 2000 in the
principal  amount of $5,828,724 (the  "Promissory  Note"),  and Prime Refractive
shall thereupon be released from any obligation under the Promissory Note.

                             Statement of Agreement

         NOW,  THEREFORE,  in consideration of the premises and mutual covenants
contained  herein and for other good,  valuable and binding  consideration,  the
receipt and  sufficiency of which are hereby  acknowledged,  the parties hereto,
intending to be legally bound hereby, agree as follows:

                                   ARTICLE I.

                             ASSIGNMENT OF INTEREST

         Section 1.1       Assignment and Grant of Warrants.
                           --------------------------------

                  (a) Prime BDR Interest.  LASIK hereby  conveys,  transfers and
assigns to PMOI,  and PMOI  hereby  acquires  from  LASIK all  right,  title and
interest  in and to the Prime BDR  Interest,  such that on the  Effective  Date,
LASIK shall not own (i) any ownership or other interest in Prime BDR or (ii) any
rights or securities  exercisable  or  exchangeable  for, or  convertible  into,
ownership or other interests in Prime BDR.

                  (b) Caster  One  Interest.  As  allowed  by Section  2.5(i) of
Caster One's  Limited  Liability  Company  Agreement,  Prime  Refractive  hereby
conveys,  transfers and assigns to Prime RVC, and Prime RVC hereby acquires from
Prime  Refractive all right,  title and interest in and to the Caster  Interest,
such  that  on the  Effective  Date,  Prime  Refractive  shall  not  own (i) any
ownership  or other  interest  in Caster  One or (ii) any  rights or  securities
exercisable  or  exchangeable  for,  or  convertible  into,  ownership  or other
interests in Caster One.

                  (c) Warrants.  In partial  consideration  of the assignment of
the  Transferred  Interests,  PMSI  agrees to deliver  warrants to LASIK (or any
combination  of  the  principals  of  LASIK  provided  in  written  instructions
delivered  to PMSI  within  5 days of the  execution  of this  Agreement),  such
warrants  to be in  substantially  the form  attached  hereto as  Exhibit K (the
"Warrants").  The Warrants delivered in partial consideration of the transfer of
the Prime BDR Interest shall entitle the holder(s) thereof to purchase, upon the
terms and  conditions  contained in the Warrants,  a collective  total of 81,263
shares of $0.01 par value common stock of PMSI, at a per share purchase price of
$10.38. The Warrants  delivered in partial  consideration of the transfer of the
Caster Interest shall entitle the holder(s) thereof to purchase,  upon the terms
and conditions contained in the Warrants, a collective total of 43,715 shares of
$0.01 par value common stock of PMSI, at a per share purchase price of $8.25.

                                   ARTICLE II.

                                    AMENDMENT

         Section 2.1       Amendments to Contribution Agreement.
                           ------------------------------------

                  (a) The Existing  Parties hereby agree to amend Section 4.3(a)
of the Contribution  Agreement to replace the reference to "Loan Agreement" with
a reference instead to "Development Facility".

                  (b) The Existing  Parties hereby agree to amend Section 4.3(e)
of the  Contribution  Agreement to replace the two references to "Loan Agreement
or Development Facility" with references instead to "Development Facility",  and
to delete the reference to "(as applicable)".

     (c) The  Existing  Parties  hereby  agree to amend  Section  4.3(f)  of the
Contribution Agreement to read in its entirety as follows:

                                    (a) The  parties  agree that all of the loan
                  agreements, promissory notes, guarantees, security agreements,
                  assignment  and  security  agreements  and  other  agreements,
                  documents or  instruments  executed by any party in connection
                  with the  Development  Facility are  hereinafter  collectively
                  referred to as the "Credit Documents."

                  (d) The Existing  Parties hereby agree to amend Section 8.2(c)
of the  Contribution  Agreement  to replace the  reference to "Exhibit A" with a
reference instead to "Exhibit K".

     (e) The Existing Parties hereby agree to amend the TABLE OF EXHIBITS to the
Contribution Agreement to add at the bottom:

                  Exhibit K                 Form of Target Center Warrants

                  (f)  The   Existing   Parties   hereby   agree  to  amend  the
Contribution Agreement to add as Exhibit K, immediately following Exhibit J, the
Form of Target Center Warrant attached to this Agreement as Exhibit K.

         Section 2.2 Assumption of Promissory Note. Prime RVC hereby assumes, as
of the Effective Date, all of the obligations arising under the Promissory Note,
and Prime  Management  agrees that Prime  Refractive is hereby released from any
and all obligations it may have under the Promissory Note, regardless of whether
such obligations are past due.  Notwithstanding the foregoing, the parties agree
that all amounts  previously paid under the Promissory Note are  non-refundable,
and each  party to this  agreement  agrees  that it will not take any  action to
recover  any  such  amount.  Prime  Management  further  agrees  that  it  shall
irrevocably cancel the Promissory Note following the assumption thereof by Prime
RVC. The existence of and amounts  advanced under the Promissory  Note shall not
reduce  the  maximum   principal   amount  of  the  Development   Facility  from
$29,165,000.

                                  ARTICLE III.

                                 REPRESENTATIONS

         Section 3.1 All Parties. Each party to this Agreement hereby represents
and warrants that (a) as of the date of this  Agreement,  it has full and lawful
power and authority to execute and deliver this  Agreement and to consummate and
perform the  transactions  contemplated  in this  Agreement,  (b)  assuming  due
execution  and  delivery  by  the  other  parties  hereto,   this  Agreement  is
enforceable   against  it,  and   constitutes  its  valid  and  legally  binding
obligation,  (c) except as  provided  herein,  it is not  required to obtain any
consent  from or  approval  or action of, or make any filing with or give notice
to, any person, public authority or entity, in connection with the execution and
delivery of this Agreement,  and (d) by virtue of its direct or indirect partial
ownership of or  involvement  with Prime BDR and Caster One, it has personal and
detailed knowledge of the operations and assets of Prime BDR and Caster One, and
it has neither requested nor relied on any additional information from any other
party to this  Agreement (or any agent or  representative  of any other party to
this Agreement).

         Section 3.2  Representations  of LASIK.  LASIK  hereby  represents  and
warrants to the parties to this  Agreement that the Prime BDR Interest is hereby
conveyed to PMOI free and clear of any and all liens,  claims,  encumbrances and
restrictions of any kind whatsoever (other than those expressly set forth in the
Contribution Agreement or the Limited Liability Company Agreement of Prime BDR).

         Section  3.3  Representations  of Prime  Refractive.  Prime  Refractive
hereby  represents and warrants to the parties to this Agreement that the Caster
Interest  is hereby  conveyed  to Prime RVC free and clear of any and all liens,
claims,  encumbrances and restrictions of any kind whatsoever  (other than those
expressly set forth in the contribution  agreement  governing Prime Refractive's
acquisition of the Caster Interest or in the Limited Liability Company Agreement
of Caster One).

                                   ARTICLE IV.

                        Resignations and ENTIRE INTEREST

         Each of Barnet,  Dulaney and Rosenberg  hereby resigns from any and all
positions  or titles  which he may hold or claim to hold with Prime BDR,  Caster
One or any  entity in which  either of the  foregoing  owns an equity  ownership
interest. Each of Barnet,  Dulaney,  Rosenberg and LASIK acknowledges and agrees
that he or it does not now have any right to purchase or otherwise  acquire,  at
any time  subsequent to the  Effective  Date,  any direct or indirect  ownership
interests in Prime BDR or Caster One.

                                   ARTICLE V.

                                     GENERAL

         Section 5.1 Subsequent Amendment of Prime BDR Governance Documents. The
parties  hereby  agree that Prime RVC and PMOI may,  at any time on or after the
Effective  Date, (a) amend,  supplement or replace  entirely the  Certificate of
Formation,  Limited  Liability  Company  Agreement  or any other  organizational
document of Prime BDR,  in any manner they desire and (b) subject to  applicable
law, dissolve Prime BDR and distribute its assets in any manner they desire.

     Section 5.2  Transaction  Document.  This  Agreement  shall be considered a
"Transaction Document" under the Contribution Agreement.

         Section 5.3 No Assumption of Liabilities.  Except as expressly provided
in Section 2.3 above,  none of PMSI, PMOI, Prime RVC or Prime Management  hereby
assumes any debt, obligation or liability of any other party to this Agreement.

         Section 5.4 Ratification by Members of Prime Refractive.  Each party to
this  Agreement  agrees that by  executing  this  Agreement,  it is deemed to be
voting its ownership  interest (if any) in Prime  Refractive to authorize  Prime
Refractive to enter into and perform this  Agreement  and any other  document or
agreement to which Prime  Refractive is a party and that is  contemplated  by or
executed in connection with this Agreement.  Each such party hereby consents (in
all  capacities  for which it is entitled to or required to give consent) to the
transfer  of the  Transferred  Interests,  and  further  agrees to execute  such
resolutions  and  written  consents,  and  take  such  other  actions,  in their
capacities  as members of Prime  Refractive,  as any other  party  hereto  shall
reasonably  require  after  the date of this  Agreement  in order to have  Prime
Refractive ratify and adopt this Agreement.

         Section  5.5  Ratification  by  Members  of LASIK.  Each  party to this
Agreement agrees that by executing this Agreement, it is deemed to be voting its
ownership  interest  (if  any) in  LASIK to  authorize  LASIK to enter  into and
perform this  Agreement and any other  document or agreement to which LASIK is a
party and that is contemplated by or executed in connection with this Agreement.
Each such party hereby  consents (in all  capacities for which it is entitled to
or required to give consent) to the transfer of the Transferred  Interests,  and
further agrees to execute such resolutions and written  consents,  and take such
other  actions,  in their  capacities  as members of LASIK,  as any other  party
hereto shall  reasonably  require  after the date of this  Agreement in order to
have LASIK ratify and adopt this Agreement.

         Section 5.6  Ratification  by Members of Prime BDR.  Each party to this
Agreement agrees that by executing this Agreement, it is deemed to be voting its
ownership  interest (if any) in Prime BDR to  authorize  Prime BDR to enter into
and perform this  Agreement  and any other  document or agreement to which Prime
BDR is a party and that is  contemplated  by or executed in connection with this
Agreement.  Each such party hereby  consents (in all  capacities for which it is
entitled  to or required to give  consent)  to the  transfer of the  Transferred
Interests,  and further agrees to execute such resolutions and written consents,
and take such other actions, in their capacities as members of Prime BDR, as any
other party hereto shall reasonably  require after the date of this Agreement in
order to have Prime BDR ratify and adopt this Agreement.

         Section 5.7       Effect on Existing Agreements.
                           -----------------------------

                  (a)  Contribution  Agreement.  This Agreement is  incorporated
into the  Contribution  Agreement by  reference.  Other than as provided in this
Agreement  and that certain  First  Amendment to  Contribution  Agreement  dated
January 31,  2000 among of the  Existing  Parties,  the  Contribution  Agreement
(including  Exhibits and  Schedules)  has not been modified or amended and is in
full force and effect.  Each of the  Existing  Parties  hereby  affirms  that it
remains a party to the  Contribution  Agreement  (as amended by this  Agreement)
after  the  execution  of this  Agreement.  The  Contribution  Agreement  may be
restated as amended hereby for the convenience of the parties hereto.

                  (b) Financing Documents.  The parties to this Agreement hereby
terminate  that  certain   Assignment  and  Security  Agreement  (the  "Security
Agreement")  dated as of  September 1, 1999  originally  between PMOI and LASIK,
securing LASIK's  obligations  under the Loan Agreement (as such term is defined
in the Contribution Agreement prior to the effect of the amendments contained in
this Agreement).  PMOI and Prime RVC agree to promptly file with the appropriate
offices a release of all financing statements securing only those obligations of
Prime BDR under the Loan Agreement.  Notwithstanding the foregoing provisions of
this  subsection,  the parties to this Agreement  acknowledge  that the Security
Agreement and such financing  statements have been collaterally  assigned to one
or more  lenders of PMSI,  and that the consent of such lenders will be required
in order  to  fully  effect  the  termination  and  releases  described  in this
subsection.  PMOI and Prime RVC hereby agree to exercise all reasonable  efforts
to promptly  have such  lenders  provide the  consents  necessary  to effect the
provisions of this subsection.

         Section 5.8  Cooperation and Further  Assurance.  From time to time, as
and when reasonably requested by another party after the date of this Agreement,
each party hereto agrees to (at the expense of the requesting party) execute and
deliver, or cause to be executed and delivered, all such documents,  instruments
and consents,  and to use reasonable efforts to take all such other actions,  as
may be reasonably requested or necessary to carry out the intent and purposes of
this Agreement and vest in Prime RVC good title to, possession of and control of
the Transferred  Interests.  Without  limiting the foregoing,  the parties agree
that the last  paragraph  of Section  9.3 of the  Contribution  Agreement  as it
relates to LASIK's  disposition of the Prime BDR Interest  hereunder  shall only
deal with the return of Proprietary Information,  credit cards, keys, equipment,
supplies and other  materials that are specific only to Prime BDR, and shall not
(as a result of the disposition of the Prime BDR Interest hereunder) require the
return of Proprietary  Information  and such items that relate both to Prime BDR
and either of Prime Refractive or Prime BDEC.

     Section 5.9 GOVERNING LAW AND  CONSTRUCTION.  THIS AGREEMENT IS PERFORMABLE
IN TRAVIS COUNTY, TEXAS, AND IS GOVERNED BY THE LAWS OF TEXAS.

         Section 5.10 ARBITRATION. ANY CONTROVERSY BETWEEN THE PARTIES REGARDING
THIS  AGREEMENT  AND ANY  CLAIMS  ARISING  OUT OF  THIS  AGREEMENT  OR A  BREACH
HEREUNDER  SHALL BE SUBMITTED TO ARBITRATION  BY THE PARTIES IN ACCORDANCE  WITH
AND GOVERNED BY SECTION 10.11 OF THE CONTRIBUTION AGREEMENT.

         Section  5.11  Severability.  If any  provision  of this  Agreement  is
rendered  or  declared  illegal or  unenforceable  by reason of any  existing or
subsequently enacted statute, rule or regulation,  or by order of or judgment of
a court,  any and all other terms and  provisions  hereof  shall  remain in full
force and effect as stated and set forth  herein.  Furthermore,  in lieu of such
illegal or unenforceable  provision,  there shall be added automatically as part
of this  Agreement,  a provision as similar in effect to the result  intended by
such  illegal or  unenforceable  provision as may be possible and still be legal
and enforceable.

         Section 5.12  Miscellaneous.  This Agreement shall be binding upon, and
shall inure to the benefit of, the parties  hereto and their  respective  heirs,
executors, administrators,  successors and permitted assigns. This Agreement may
be executed in multiple  counterparts,  each of which shall be an original,  but
all of which shall  constitute one and the same  instrument.  This Agreement has
been negotiated by the parties and their  respective  counsel and will be fairly
interpreted in accordance with its terms and without any strict  construction in
favor of or against  any party.  When the  context  requires,  the gender of all
words used herein  shall  include  the  masculine,  feminine  and neuter and the
number of all words shall include the singular and plural.  The captions in this
Agreement are for convenience of reference only and shall not limit or otherwise
affect  any of  the  terms  or  provisions  hereof.  There  are  no  third-party
beneficiaries to this Agreement. This Agreement may not be modified,  altered or
amended  except by a writing signed by all of the parties  hereto.  No waiver of
any provisions hereof shall be effective unless contained in a writing signed by
the person to be bound thereby.

                            [Signature page follows]


<PAGE>




S-4

                                 SIGNATURE PAGE

                                       TO

                              ASSIGNMENT AGREEMENT

                                       AND

                   SECOND AMENDMENT TO CONTRIBUTION AGREEMENT

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed and delivered on the day and year first above written.

PMSI:                                       PRIME MEDICAL SERVICES, INC.



                                            Teena Belcik, Treasurer

PMOI:                               PRIME MEDICAL OPERATING, INC.



                                            Teena Belcik, Treasurer

PRIME RVC:                          PRIME RVC, INC.



                                            Teena Belcik, Treasurer

PRIME MANAGEMENT:          PRIME REFRACTIVE MANAGEMENT, L.L.C.

                                            Teena Belcik, Treasurer

BDEC:                               Barnet Dulaney Eye CENTER, P.L.L.C.

                                            By:
                         David D. Dulaney, M.D., manager

LASIK:                              LASIK INVESTORS, L.L.C.


                                            By:
                         Ronald W. Barnet, M.D., manager

                                            By:
                         David D. Dulaney, M.D., manager

PRIME BDR:                          PRIME/BDR ACQUISITION, L.L.C.

Ronald W.  Barnet,  M.D.,  signing as a manager of Prime BDR,
  and on behalf of LASIK as a member of Prime BDR



David D.  Dulaney,  M.D.,  signing as a manager  of Prime BDR,
  and on behalf of LASIK as a member of Prime BDR



Teena  Belcik,  signing  as a manager  of Prime  BDR,
         and on behalf of PMOI as a member of Prime BDR



PRIME BDEC:                         PRIME/BDEC ACQUISITION, L.L.C.

Ronald W.  Barnet,  M.D.,  signing as a manager of Prime BDEC,
          and on behalf of LASIK as a member of Prime BDEC


David D.  Dulaney,  M.D.,  signing as a manager of Prime BDEC,
          and on behalf of LASIK as a member of Prime BDEC

Teena  Belcik,  signing  as a manager of Prime  BDEC,
          and on behalf of PMOI as a member of Prime BDEC



PRIME REFRACTIVE:          PRIME REFRACTIVE, L.L.C.

Ronald W. Barnet,  M.D.,  signing as a manager of Prime Refractive,
          and on behalf of LASIK as a member of Prime Refractive

David D. Dulaney,  M.D.,  signing as a manager of Prime Refractive,
          and on behalf of LASIK as a member of Prime Refractive

Teena Belcik,  signing as a manager of Prime Refractive,
          and on behalf of PMOI as a member of Prime Refractive



DULANEY:

                                            David D. Dulaney, M.D.



BARNET:

                                            Ronald W. Barnet, M.D.



ROSENBERG:

                                            Mark Rosenberg