REVOLVING CREDIT NOTE



$6,666,666.67              Boston, Massachusetts               March 31, 1997


     FOR VALUE RECEIVED, the undersigned, PRIME MEDICAL SERVICES, INC., a
Delaware corporation ("MAKER"), hereby promises to pay to the order of
IMPERIAL BANK ("PAYEE"), at the offices of The First National
Bank of Boston, as Administrative Agent (together with any successor as provided
in the Agreement, hereinbelow defined, the "ADMINISTRATIVE AGENT") at 100
Federal Street, Boston, Massachusetts, on April 30, 2001, in lawful money of the
United States of America, the principal sum of SIX MILLION SIX HUNDRED
SIXTY-SIX THOUSAND SIX HUNDRED SIXTY-SIX AND 67/100 DOLLARS
($6,666,666.67), or so much thereof as may be advanced and outstanding
hereunder together with the interest on the outstanding principal balance from
day to day remaining, as herein specified.

     This Note has been executed and delivered by Maker pursuant to the terms of
that certain Second Amended and Restated Loan Agreement of even date herewith
among Maker, Payee, the Administrative Agent and each of the other Lenders which
is or may become a party thereto or any successor or assignee thereof (as the
same may be amended, supplemented or modified from time to time, the
"AGREEMENT") and is one of the Revolving Credit Notes described therein.
Capitalized terms used and not otherwise defined herein shall have the same
meanings as set forth in the Agreement.

     Reference is hereby made to the Agreement for provisions affecting this
Note, including, without limitation, provisions regarding payments, prepayments
(optional and mandatory), Events of Default and the Administrative Agent's and
Payee's right as a result of the occurrence thereof.

     The outstanding principal balance hereof shall bear interest prior to
maturity at a varying rate per annum which shall from day to day be equal to the
lesser of (a) the Maximum Rate, or (b) the Applicable Rate in effect from day to
day, each such change in the rate of interest charged hereunder to become
effective, without notice to Maker, on the effective date of each change in the
Applicable Rate or the Maximum Rate, as the case may be; provided, however, if
at any time the Applicable Rate shall exceed the Maximum Rate, thereby causing
the interest rate hereon to be limited to the Maximum Rate, then any subsequent
reduction in the Applicable Rate shall not reduce the rate of interest hereon
below the Maximum Rate until the total amount of interest accrued hereon equals
the amount of interest which would have accrued hereon if the Applicable Rate
had at all times been in effect. Accrued and unpaid interest on this Note shall
be due and payable on each Payment Date and on the Termination Date. All past-
due principal and interest shall bear interest as the Default Rate.

     Notwithstanding anything to the contrary contained herein, no provisions of
this Note shall require the payment or permit the collection of interest in
excess of the Maximum Rate.  If and excess of interest in such respect is herein
provided for, or shall be adjudicated to be so provided, in this Note or
otherwise in connection with this loan transaction, the provisions of this
paragraph shall govern and prevail, and neither Maker nor the sureties,
guarantors, successors or assigns of Maker shall be obligated to pay the excess
amount of such interest, or any other excess sum paid for the use, forbearance
or detention of sums loaned pursuant hereto.  If for any reason interest in
excess of the Maximum Rate shall be deemed charged, required or permitted by any
court of competent jurisdiction, any such excess shall be applied as a payment
and reduction of the principal of indebtedness evidenced by this Note; and, if
the principal amount hereof has been paid in
<PAGE>

full, any remaining excess shall forthwith be paid to Maker. In determining
whether or not the interest paid or payable exceeds the Maximum Rate, Maker, the
Administrative Agent and Payee shall, to the extent permitted by applicable law,
(i) characterize any non-principal payment as an expense, fee, or premium rather
than as interest, (ii) exclude voluntary prepayments and the effects thereof,
and (iii) amortize, prorate, allocate, and spread in equal or unequal parts the
total amount of interest throughout the entire contemplated term of the
indebtedness evidenced by this Note so that the interest for the entire term
does not exceed the Maximum Rate.

     Upon the occurrence of an Event of Default, the Administrative Agent may
(and if directed by the Required Lenders, shall) declare the entire unpaid
principal of and accrued interest on this Note immediately due and payable
without notice, demand or presentment, all of which are hereby waived, and upon
such declaration, the same shall become and shall be immediately due and
payable, and the Administrative Agent shall have the right to foreclose or
otherwise enforce all Liens or security interests securing payment hereof, or
any part hereof, and offset against this Note any sum or sums owed by the
Administrative Agent, Payee or the holder hereof to Maker.  Failure of the
Administrative Agent, Payee or the holder hereof to exercise this option shall
not constitute a waiver of the right to exercise the same upon the occurrence of
a subsequent Event of Default.

     If the Administrative Agent, Payee or the holder hereof expends any effort
in any attempt to enforce payment of all or any part or installment of any sum
due the holder hereunder, or if this Note is placed in the hands of an attorney
for collection, or if it is collected through any legal proceedings, Maker
agrees to pay all costs, expenses, and fees incurred by the Administrative
Agent, or the holder, including reasonable attorneys' fees.

     This Note shall be governed by and construed in accordance with the laws of
the Commonwealth of Massachusetts and the applicable laws of the United States
of America.

     Except as provided in the Agreement, Maker and each surety, guarantor,
endorser, and other party ever liable for payment of any sums of money payable
on this Note jointly and severally waive notice, presentment, demand for
payment, protest, notice of protest and non-payment or dishonor, notice of
acceleration, notice of intent to accelerate, notice of intent to demand,
diligence in collecting, grace, and all other formalities of any kind, and
consent to all extensions without notice for any period or periods of time and
partial payments, before or after maturity, and any impairment of any Collateral
securing this Note, all without prejudice to the Administrative Agent, Payee or
the holder.  The Administrative Agent, Payee and the holder shall similarly have
the right to deal in any way, at any time, with one or more of the foregoing
parties without notice to any other party, and to grant any such party any
extensions of time for payment of any of said indebtedness, or to release or
substitute part or all of the Collateral securing this Note, or to grant any
other indulgences or forbearances whatsoever, without notice to any other party
and without in any way affecting the personal liability of any party hereunder.

     Maker hereby authorizes the Administrative Agent, Payee and the holder
hereof to endorse on the SCHEDULE attached to this Note or any continuation
thereof or to record in their internal records all Advances made to Maker
hereunder and all payments made on account of the principal thereof, which
endorsements or recordings shall be prima facie evidence as to the outstanding
principal amount of this Note; provided, however, any failure by the
Administrative Agent, Payee or the holder hereof to make any such endorsement or
recording shall not limit or otherwise affect the obligations of Maker under the
Agreement or this Note.

                                      -2-
<PAGE>

     [This Note, together with all the other Revolving Credit Notes issued on
the date hereof are given in renewal, amendment, increase and restatement, but
not extinguishment, of the Revolving Credit Notes issued under the Amended and
Restated Loan Agreement dated as of April 26, 1996 among Maker, NationsBank, the
Administrative Agent, and each of the other Lenders party thereto.]

                                       PRIME MEDICAL SERVICES, INC.



                                       By: /s/ Cheryl Williams
                                          --------------------------------------
                                           Cheryl Williams
                                           Vice President-Finance

                                      -3-
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                                   SCHEDULE

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      Date           Advance           Principal Payment            Balance
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