PROMISSORY NOTE
Austin, Texas                    (LINE OF CREDIT)             September 1, 1999



PROMISE TO PAY: For value  received,  the undersigned  Borrower  (whether one or
more) promises to pay to the order of Lender the Principal Amount, to the extent
advanced by Lender, together with interest on the unpaid balance of such amount,
in lawful  money of the United  States of America,  in  accordance  with all the
terms, conditions,  and covenants of this Note and the Loan Documents identified
below.

     BORROWER:  Prime/BDR  Acquisition,  L.L.C.,  a Delaware  limited  liability
company
     BORROWER'S ADDRESS FOR NOTICE:  1301 Capital of Texas Highway,  Suite C-300
Austin, Texas 78746 Attention: President
LENDER:           Prime Medical Operating, Inc., a Delaware corporation

     LENDER'S ADDRESS FOR PAYMENT:  1301 Capital of Texas Highway,  Suite C-300,
Austin, Texas 78746 Attention: Chief Financial Officer
PRINCIPAL AMOUNT:  Two Hundred Thousand Dollars ($200,000)

INTEREST RATE:  Fifteen Percent (15%)

PAYMENT  TERMS:  Interest on the unpaid  balance of this Note is due and payable
quarterly,  beginning  November 1, 1999, and continuing  regularly and quarterly
thereafter on or before the first day of February,  May, August, until September
1, 2000 (the "Maturity  Date"),  when the outstanding  principal balance and all
accrued  interest shall be due and payable in full.  Interest will be calculated
on the unpaid  principal  balance.  Each payment  will be credited  first to the
accrued interest and then to the reduction of principal.

REVOLVING  LINE OF  CREDIT:  This Note  evidences  a  revolving  line of credit.
Subject to the terms of the Loan Agreement  between  Borrower and Lender of even
date  herewith,  all or any portion of the Principal  Amount of this Note may be
borrowed, paid, prepaid, repaid, and reborrowed,  from time to time prior to the
Maturity  Date and in accordance  with the Loan  Documents.  Each  borrowing and
repayment  hereunder will be (i) endorsed on an attachment to this Note, or (ii)
entered  in the books and  records of  Lender.  The books and  records of Lender
shall be prima facie  evidence  of all sums due  Lender.  If an event of default
exists  under  this Note or any Loan  Document,  then  Lender  shall be under no
obligation to make any advance under this Note.

     LOAN  AGREEMENT:  This Note is executed  pursuant to and is governed by the
terms of the Loan  Agreement  of even date  herewith,  executed by Borrower  and
Lender, as amended (collectively, the "Loan Agreement").
1.       INTEREST PROVISIONS:

Rate:  The  principal  balance of this Note from time to time  remaining  unpaid
prior to maturity  shall bear  interest at the  Interest  Rate per annum  stated
above.  Interest  shall be  calculated  on the  amount  of each  advance  of the
Principal Amount of this Note from the date of each such advance.

Maximum  Lawful Interest:  The term "Maximum Lawful Rate" means the maximum rate
         of interest  and the term  "Maximum  Lawful  Amount"  means the maximum
         amount  of  interest  that is  permissible  under  applicable  state or
         federal law for the type of loan  evidenced  by this Note and the other
         Loan  Documents.  If the Maximum Lawful Rate is increased by statute or
         other governmental action subsequent to the date of this Note, then the
         new  Maximum  Lawful  Rate  shall be  applicable  to this Note from the
         effective date thereof, unless otherwise prohibited by applicable law.

Spreadingof Interest:  Because of the possibility of irregular periodic balances
         of principal or premature payment,  the total interest that will accrue
         under this Note cannot be determined in advance. Lender does not intend
         to contract for,  charge,  or receive more than the Maximum Lawful Rate
         or Maximum Lawful Amount  permitted by applicable state or federal law,
         and to prevent such an  occurrence  Lender and Borrower  agree that all
         amounts of interest,  whenever  contracted for, charged, or received by
         Lender, with respect to the loan of money evidenced by this Note, shall
         be spread,  prorated,  or  allocated  over the full period of time this
         Note is unpaid,  including  the period of any renewal or  extension  of
         this Note.  If demand for payment of this Note is made by Lender  prior
         to the full stated term, the total amount of interest  contracted  for,
         charged,  or  received  to the time of such  demand  shall  be  spread,
         prorated, or allocated along with any interest thereafter accruing over
         the full period of time that this Note  thereafter  remains  unpaid for
         the purpose of determining if such interest  exceeds the Maximum Lawful
         Amount.

Excess   Interest:  At maturity  (whether by  acceleration  or  otherwise) or on
         earlier  final  payment of this Note,  Lender  shall  compute the total
         amount of interest that has been contracted for,  charged,  or received
         by Lender or  payable by  Borrower  under  this Note and  compare  such
         amount to the Maximum  Lawful  Amount  that could have been  contracted
         for, charged, or received by Lender. If such computation  reflects that
         the total amount of interest that has been contracted for, charged,  or
         received  by Lender or payable by Borrower  exceeds the Maximum  Lawful
         Amount,  then Lender  shall apply such excess to the  reduction  of the
         principal balance and not to the payment of interest; or if such excess
         interest  exceeds the unpaid  principal  balance,  such excess shall be
         refunded to Borrower. This provision concerning the crediting or refund
         of excess  interest  shall control and take  precedence  over all other
         agreements  between  Borrower and Lender so that under no circumstances
         shall the total interest contracted for, charged, or received by Lender
         exceed the Maximum Lawful Amount.

Interest After Default:  At Lender's option,  the unpaid principal balance shall
         bear interest after maturity  (whether by acceleration or otherwise) at
         the "Default  Interest  Rate." The Default  Interest  Rate shall be, at
         Lender's  option,  (i) the Maximum  Lawful Rate, if such Maximum Lawful
         Rate is established by applicable law; or (ii) the Interest Rate stated
         on the first page of this Note plus five (5) percentage  points,  if no
         Maximum Lawful Rate is established by applicable law; or (iii) eighteen
         percent (18%) per annum; or (iv) such lesser rate of interest as Lender
         in its sole  discretion  may choose to charge;  but never more than the
         Maximum  Lawful Rate or at a rate that would  cause the total  interest
         contracted  for,  charged,  or received by Lender to exceed the Maximum
         Lawful Amount.

Daily Computation of Interest: To the extent permitted by applicable law, Lender
at its option will  calculate  the per diem interest rate or amount based on the
actual  number of days in the year (365 or 366, as the case may be),  and charge
that per diem interest rate or amount each day. In no event shall Lender compute
the interest in a manner that would cause  Lender to contract  for,  charge,  or
receive interest that would exceed the Maximum Lawful Rate or the Maximum Lawful
Amount

DEFAULT PROVISIONS:

EVENTS OF DEFAULT AND  ACCELERATION  OF MATURITY:  LENDER MAY, AFTER THIRTY (30)
DAYS'  WRITTEN  NOTICE TO BORROWER  AND  BORROWER'S  FAILURE TO CURE WITHIN SUCH
30-DAY  PERIOD  AND  WITHOUT  FURTHER  NOTICE OR DEMAND,  (except  as  otherwise
required  by  statute),  ACCELERATE  THE  MATURITY  OF THIS NOTE AND DECLARE THE
ENTIRE UNPAID PRINCIPAL BALANCE AND ALL ACCRUED INTEREST AT ONCE DUE AND PAYABLE
IF:

         There is  default  in the  payment  of any  installment  of  principal,
interest,  or any other sum  required to be paid under the terms of this Note or
any of the Loan Documents; or

         There is a breach or  default  (other  than by Lender or Prime  Medical
Services,  Inc.)  under this Note or any of the Loan  Documents,  including  any
instrument  securing the payment of this Note or any loan agreement  relating to
the advance of loan proceeds.

WAIVER   BY  BORROWER:  EXCEPT AS PROVIDED IN  PARAGRAPH  2(a) HEREOF AND IN ANY
         OTHER LOAN  DOCUMENT,  BORROWER AND ALL OTHER  PARTIES  LIABLE FOR THIS
         NOTE  WAIVE,  DEMAND,  NOTICE  OF  INTENT TO  DEMAND,  PRESENTMENT  FOR
         PAYMENT,  NOTICE OF  NONPAYMENT,  PROTEST,  NOTICE OF  PROTEST,  GRACE,
         NOTICE OF DISHONOR,  NOTICE OF INTENT TO ACCELERATE MATURITY, NOTICE OF
         ACCELERATION  OF MATURITY,  AND  DILIGENCE IN  COLLECTION.  EACH MAKER,
         SURETY,  ENDORSER,  AND GUARANTOR OF THIS NOTE WAIVES AND AGREES TO ONE
         OR MORE  EXTENSIONS  FOR ANY PERIOD OR PERIODS OF TIME, AND ANY PARTIAL
         PAYMENTS, BEFORE OR AFTER MATURITY,  WITHOUT PREJUDICE TO THE HOLDER OF
         THIS NOTE. EACH MAKER, SURETY, ENDORSER, AND GUARANTOR WAIVES NOTICE OF
         ANY AND ALL RENEWALS, EXTENSIONS,  REARRANGEMENTS, AND MODIFICATIONS OF
         THIS NOTE.

Non-Waiver by Lender:  Any previous extension of time,  forbearance,  failure to
pursue some  remedy,  acceptance  of late  payments,  or  acceptance  of partial
payment by Lender,  before or after  maturity,  does not  constitute a waiver by
Lender of its subsequent  right to strictly  enforce the collection of this Note
according to its terms.

Other  Remedies Not  Required:  Lender shall not be required to first file suit,
exhaust all  remedies,  or enforce its rights  against any  security in order to
enforce payment of this Note.

Joint and Several  Liability:  Each Borrower who signs this Note, and all of the
other  parties  liable  for the  payment  of  this  Note,  such  as  guarantors,
endorsers,  and sureties,  are jointly and  severally  liable for the payment of
this Note.

Attorney's  Fees: If Lender  requires the services of an attorney to enforce the
payment of this Note or the performance of the other Loan Documents,  or if this
Note is collected through any lawsuit,  probate,  bankruptcy,  or other judicial
proceeding,  Borrower  agrees to pay  Lender an amount  equal to its  reasonable
attorney's fees and other collection  costs.  This provision shall be limited by
any applicable statutory  restrictions  relating to the collection of attorney's
fees.

3.       MISCELLANEOUS PROVISIONS:

Subsequent Holder: All references to Lender in this Note shall also refer to any
subsequent owner or holder of this Note by transfer, assignment, endorsement, or
otherwise.

Transfer:Borrower  acknowledges and agrees that Lender may transfer this Note or
         partial   interests  in  the  Note  to  one  or  more   transferees  or
         participants,  including without  limitation  transfers provided for in
         Section  8.10 of the Loan  Agreement.  Borrower  authorizes  Lender  to
         disseminate  to any  such  transferee  or  participant  or  prospective
         transferee or participant any information it has pertaining to the loan
         evidenced  by  this  Note,   including,   without  limitation,   credit
         information  on Borrower and any  guarantor of this Note and any of the
         type of information described in Section 8.10 of the Loan Agreement.

Other  Parties  Liable:  All  promises,  waivers,   agreements,  and  conditions
applicable  to Borrower  shall  likewise be  applicable  to and binding upon any
other  parties  primarily  or  secondarily  liable for the payment of this Note,
including all guarantors, endorsers, and sureties.

Successors  and Assigns:  The  provisions of this Note shall be binding upon and
for the benefit of the successors, assigns, heirs, executors, and administrators
of Lender and Borrower.

No Duty or Special  Relationship:  Borrower acknowledges that Lender has no duty
of good faith to Borrower,  and Borrower acknowledges that no fiduciary,  trust,
or other special relationship exists between Lender and Borrower.

Modifications:  Any modifications agreed to by Lender relating to the release of
liability of any of the parties primarily or secondarily  liable for the payment
of this Note, or relating to the release,  substitution, or subordination of all
or part of the security for this Note,  shall in no way  constitute a release of
liability  with  respect to the other  parties or  security  not covered by such
modification.

Entire  Agreement:  Borrower  warrants and  represents  that the Loan  Documents
constitute the entire agreement  between Borrower and Lender with respect to the
loan  evidenced  by this Note and agrees  that no  modification,  amendment,  or
additional  agreement  with  respect  to such loan or the  advancement  of funds
thereunder will be valid and  enforceable  unless made in writing signed by both
Borrower and Lender.

Borrower's  Address  for Notice:  All  notices  required to be sent by Lender to
Borrower shall be sent by U.S. Mail, postage prepaid,  to Borrower's Address for
Notice stated on the first page of this Note, until Lender shall receive written
notification from Borrower of a new address for notice.

Lender's  Address for  Payment:  All sums payable by Borrower to Lender shall be
paid at Lender's  Address for Payment  stated on the first page of this Note, or
at such other address as Lender shall designate from time to time.

Business Use:  Borrower  warrants and  represents to Lender that the proceeds of
this Note will be used solely for business or commercial purposes, and in no way
will the proceeds be used for personal, family, or household purposes.

Chapter 15 Not Applicable:  It is understood that Chapter 15 of the Texas Credit
Code relating to certain  revolving credit loan accounts and tri-party  accounts
is not applicable to this Note.

APPLICABLE  LAW: THIS NOTE HAS BEEN EXECUTED AND DELIVERED IN TEXAS AND SHALL BE
CONSTRUED IN ACCORDANCE  WITH THE APPLICABLE  LAWS OF THE STATE OF TEXAS AND THE
LAWS OF THE UNITED STATES OF AMERICA APPLICABLE TO TRANSACTIONS IN TEXAS.

4.       LOAN DOCUMENTS:

This Note.

The Loan Agreement and the Loan Documents as defined therein.

All      other  documents  signed in connection  with the Loan  Agreement or the
         loan  evidenced  by this  Note,  including,  without  limitation,  that
         certain  Contribution  Agreement,  dated  effective  September 1, 1999,
         between and among Borrower,  Lender,  Prime Medical  Services,  Inc., a
         Delaware  corporation,   Prime/BDEC  Acquisition,  L.L.C.,  a  Delaware
         limited  liability  company,  Barnet Dulaney Eye Center,  P.L.L.C.,  an
         Arizona  professional  limited  liability  company,   LASIK  Investors,
         L.L.C., a Delaware limited liability company,  David D. Dulaney,  M.D.,
         Ronald  W.  Barnet,   M.D.,  and  Mark  Rosenberg  (the   "Contribution
         Agreement") and each  Transaction  Document (as such term is defined in
         the Contribution Agreement).

                                              [Signature page follows]



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                                                  SIGNATURE PAGE TO
                                                   PROMISSORY NOTE


EXECUTED this 1 day of September, 1999.



                 BORROWER:

             PRIME/BDR ACQUISITION, L.L.C., a Delaware limited liability company



                                  By: /s/ Ronald W. Barnet, M.D.

                                  Printed Name: Ronald W. Barnet, M.D.

                                  Title: Manager



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