Exhibit 10.50
                                PROMISSORY NOTE
Austin, Texas                   (LINE OF CREDIT)                January 1, 1998


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:  Barton Acquisition, Inc., a Texas corporation

BORROWER'S  ADDRESS FOR NOTICE:  1301 Capital of Texas  Highway,  Suite  C-300, 
                                 Austin,  Texas  78746,  Attention:
John H. Trevey

LENDER:  American Physicians Service Group, Inc., a Texas corporation

LENDER'S ADDRESS FOR PAYMENT:   1301 Capital of Texas Highway, Suite C-300, 
                                Austin, Texas  78746

PRINCIPAL AMOUNT:  Two Million Four Hundred Thousand Dollars and No/100 Dollars 
                   ($2,400,000.00)

INTEREST RATE:  Ten Percent (10.0%)

PAYMENT  TERMS:  Interest  only on the  unpaid  balance  of this Note is due and
payable  quarterly,  beginning  June  1,  1998,  and  continuing  regularly  and
quarterly  thereafter on or before the first day of March,  June,  September and
December of each year,  until January 1, 2003 (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:

         (a)  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.
<PAGE>

         (b) 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.

         (c)  SPREADING OF  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.

         (d) 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.

         (e) 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.

         (f)  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.

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<PAGE>

2.       DEFAULT PROVISIONS:

         (a) 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:

                  (i) 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

                  (ii)  There is  default in the  performance  of any  covenant,
         condition,  or  agreement  contained  in 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.

         (b) 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.

         (c) 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.

         (d) 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.

         (e) 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.

         (f) 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:

         (a) 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.

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<PAGE>

         (b) TRANSFER: Borrower acknowledges and agrees that Lender may transfer
this  Note or  partial  interests  in the  Note to one or  more  transferees  or
participants.  Borrower  authorizes Lender to disseminate 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,  to any such
transferee or participant or prospective transferee or participant.

         (c) 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.

         (d)  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.

         (e) 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.

         (f)  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.

         (g) 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.

         (h) 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.

         (i)  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.

         (j) 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.

         (k) 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.

         (l) 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.

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<PAGE>

4.       LOAN DOCUMENTS:

     (a)      This Note consisting of this page and the preceding 4 pages.
     (b)      The Loan Agreement of even date.
     (c)      The Deed of Trust (Security  Agreement,  Assignment of Leases and
               Rents and Financing  Statement) securing this Note.
     (d)      The Security Agreement securing this Note.
     (e)      All other  documents signed in connection with the loan  evidenced
                by this Note.

         EXECUTED this 16th day of March, 1998.

                         BORROWER:

                         BARTON ACQUISITION, INC., a Texas corporation


                         By:    /s/  John H. Trevey                             
                         Name:       John H. Trevey                             
                         Title:      CEO                                      



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