Pledge and Security Agreement



                          PLEDGE AND SECURITY AGREEMENT

         THIS  PLEDGE  AND  SECURITY  AGREEMENT  (the  "Agreement")  dated as of
January 31,  2000,  is by and between OHIO LITHO,  INC., a Delaware  corporation
("Pledgor"), whose street address is 1301 Capital of Texas Highway, Suite C-300,
Austin, Texas 78746-6550,  for the benefit of BANK OF AMERICA,  N.A., a national
banking association ("B of A"), whose street address is 901 Main Street, Dallas,
Texas 75202, not in its individual  capacity but solely as administrative  agent
for itself and each of the other banks or lending institutions (each, a "Lender"
and collectively, the "Lender") which is or may from time to time become a party
to the Loan Agreement (as hereinbelow defined) (in such capacity,  together with
its successors in such capacity, the "Administrative Agent").

                                R E C I T A L S:

     A. Prime Medical Services, Inc., a Delaware corporation  ("Borrower"),  has
entered into that certain Fourth Amended and Restated Loan Agreement dated as of
the date hereof with B of A as Administrative Agent and as a Lender, BankBoston,
N.A., as Documentation Agent and as a Lender, and the other Lenders from time to
time party thereto, as amended,  waived, restated, and supplemented from time to
time ("Loan Agreement").

         B. Pledgor and certain  other  guarantors  have  executed  that certain
Guaranty  Agreement  dated as of the date  hereof  (as the same may be  amended,
supplemented or modified from time to time, the  "Guaranty"),  pursuant to which
Pledgor has guaranteed to the Agents (as defined in the Loan  Agreement) and the
Lenders  the full and  complete  payment  and  performance  of the  liabilities,
obligations,  and  indebtedness  of the  Borrower  to the Agents and the Lenders
under the Loan Documents (as defined in the Loan Agreement).

     C. As a condition to entering into the Loan Agreement, Pledgor must execute
and deliver this Agreement.

         NOW  THEREFORE,  in  consideration  of the  premises and other good and
valuable  consideration,  the  receipt  and  sufficiency  of  which  are  hereby
acknowledged, Pledgor agrees with the Administrative Agent as follows:

                                    ARTICLE I

                                   DEFINITIONS

         (a) Each term used herein and defined in the Loan Agreement  shall have
the  meaning  assigned to it in the Loan  Agreement,  unless  otherwise  defined
herein or the context otherwise requires.

         (b) In addition,  as used herein,  the  following  terms shall,  unless
otherwise indicated, have the following meanings:

         "Borrower" has the meaning set forth in the recitals.

         "Code" shall mean the Uniform Commercial Code as in effect in the State
of Texas.


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                                                   Pledge and Security Agreement

                                        3



         "Collateral"  shall mean the assets and interests of Pledgor identified
in Section 2.1 hereof.

         "Event of  Default"  shall have the  meaning  assigned  to such term in
Section 5.1.

         "Guaranty" shall mean that certain  Guaranty  Agreement dated as of the
date hereof, executed by Pledgor and certain other guarantors for the benefit of
the Agents and the Lenders, guaranteeing the full payment and performance of the
Obligations, as amended, modified, confirmed, and extended from time to time.

         "Partnerships"  shall mean (a) those partnerships and limited liability
companies  listed on  Exhibit  A  attached  hereto  and  incorporated  herein by
reference,  as such  partnerships  or limited  liability  companies exist or may
hereinafter be restated,  amended or restructured,  (b) any  partnership,  joint
venture,  or limited  liability  company in which  Pledgor  shall,  at any time,
become  a  limited  or  general  partner,   venturer,  or  member,  or  (c)  any
partnership, joint venture or corporation formed as a result of the restructure,
reorganization or amendment of the Partnerships.

         "Partnership  Agreements"  shall  mean (a) those  agreements  listed on
Exhibit B attached hereto and  incorporated  herein by reference  (together with
any  modifications,  amendments or  restatements  thereof),  and (b) partnership
agreements,  joint venture agreements,  or organizational  agreements for any of
the partnerships,  joint ventures,  or limited liability  companies described in
clause  (b) of  the  definition  of  "Partnerships"  above  (together  with  any
modifications,  amendments or restatements thereof), and "Partnership Agreement"
means any one of the Partnership Agreements.

         "Pledged Partnership Interests" shall mean all of Pledgor's partnership
interests,  whether general or limited, venture, or membership interests, in the
Partnerships,  including,  without limitation, all of Pledgor's right, title and
interest now or hereafter accruing under the Partnership Agreements with respect
to any  interest  now owned or  hereafter  acquired  or owned by  Pledgor in the
Partnerships,  and including all  distributions,  allocations,  proceeds,  fees,
preferences,  payments or other benefits,  which Pledgor now is or may hereafter
become  entitled to receive with respect to such  interests in the  Partnerships
and with respect to the repayment of all loans now or hereafter  made by Pledgor
to the Partnerships,  and Pledgor's undivided  percentage interest in the assets
of the Partnerships.

         "Secured  Indebtedness" shall have the meaning assigned to such term in
Section 2.1(c) hereof.

         "Security Interests" shall mean the pledge, collateral assignment,  and
security interests securing the Secured  Indebtedness,  including (i) the pledge
and  security  interest in the  Pledged  Partnership  Interests  granted in this
Agreement  and  (ii)  all  other  security  interests  created  or  assigned  as
additional security for the Secured  Indebtedness  pursuant to the provisions of
this Agreement.

         (c) Whenever the context so requires,  the neuter  gender  includes the
masculine and  feminine,  and the singular  number  includes the plural and vice
versa.


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                                   ARTICLE II

                            COLLATERAL AND OBLIGATION

         SECTION 2.1       Grant of Security Interest.
                           --------------------------

         (a) As collateral  security for Secured  Indebtedness,  Pledgor  hereby
pledges and grants to the Administrative  Agent, for the benefit of the Lenders,
a first  priority  lien on and  security  interest  in and to,  and  agrees  and
acknowledges  that the  Administrative  Agent has, and shall continue to have, a
security interest in and to, and assigns, transfers,  pledges and conveys to the
Administrative  Agent, all of Pledgor's right,  title and interest in and to the
following  described  collateral  (the  "Collateral")  now  owned  or  hereafter
acquired,  wherever  located,  howsoever  arising or  created,  and  whether now
existing or hereafter arising, existing or created:

                    (i)  the  Pledged  Partnership  Interests  and all rights of
                         Pledgor with respect  thereto and all proceeds,  income
                         and profits therefrom;

                  (ii)     all of Pledgor's  distribution rights, income rights,
                           liquidation  interest,   accounts,  contract  rights,
                           general intangibles,  notes, instruments,  drafts and
                           documents   relating  to  the   Pledged   Partnership
                           Interests;

                  (iii)    to the extent attributable to the Pledged Partnership
                           Interests,  all promissory  notes,  notes receivable,
                           accounts,  accounts  receivable and instruments owned
                           or held by Pledgor or, in which Pledgor owns or holds
                           an   interest,    evidencing   obligations   of   the
                           Partnerships;

                  (iv)     all liens, security interests,  collateral,  property
                           and  assets  securing  any of the  promissory  notes,
                           notes receivables,  instruments,  accounts receivable
                           and other  claims and  interest  described  in clause
                           (iii) above;

                    (v)  all books, files, computer records,  computer software,
                         electronic  information  and other  files,  records  or
                         information  relating  to any or all of the  foregoing;
                         and

                  (vi)     all substitutions,  replacements, products, proceeds,
                           income and profits arising from any of the foregoing;
                           including without limitation insurance proceeds.

         (b)  The  Security   Interests  are  granted  and  the   Collateral  is
collaterally  assigned as security only and shall not subject the Administrative
Agent or any holder of the  Secured  Indebtedness  to, or transfer or in any way
affect or modify,  any obligation or liability of Pledgor with respect to any of
the Collateral.

         (c)  The   Collateral   shall   secure   the   following   obligations,
indebtedness,  and liabilities  (whether at stated maturity,  by acceleration or
otherwise)  (all  such   obligations,   indebtedness,   and  liabilities   being
hereinafter sometimes called the "Secured Indebtedness"):

                    (i)  the  Obligations and the  obligations,  liabilities and
                         indebtedness  of Pledgor to the Agents and the  Lenders
                         under the Guaranty;



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                  (ii)     all reasonable costs and expenses, including, without
                           limitation,  all reasonable attorneys' fees and legal
                           expenses, incurred by any of the Agents or any Lender
                           to preserve and maintain the Collateral,  collect the
                           obligations   herein  described,   and  enforce  this
                           Agreement; and

          (iii)all  extensions,  renewals,  and  modifications  of  any  of  the
               foregoing.

     SECTION 2.2 Consent.  To the extent any Partnership  Agreement requires the
consent or agreement of Pledgor to the transfer,  conveyance,  or encumbrance as
security  for the  Secured  Indebtedness  of all or any  portion of the  Pledged
Partnership  Interests,  Pledgor hereby irrevocably consents to (a) the grant of
the security  interest  described in Section 2.1 of this Agreement,  and (b) any
transfer or  conveyance  of the Pledged  Partnership  Interests  pursuant to the
Administrative  Agent's exercise of its rights and remedies under Section 5.4 of
this Agreement or under any other Loan Document.

         SECTION 2.3 Pledgor  Remains  Liable.  Notwithstanding  anything to the
contrary contained herein, (a) Pledgor shall remain liable under the Partnership
Agreements  to the  extent set forth  therein  to perform  all of its duties and
obligations  thereunder  to the same  extent as if this  Agreement  had not been
executed  (b) the  exercise  by the  Administrative  Agent of any of its  rights
hereunder shall not release Pledgor from any of its duties or obligations  under
the contracts and  agreements  included in the  Collateral,  and (c) neither the
Administrative Agent nor any Lender shall have any obligation or liability under
the  Partnership  Agreements  by  reason  of  this  Agreement,   nor  shall  the
Administrative  Agent  or  any  Lender  be  obligated  to  perform  any  of  the
obligations or duties of Pledgor  thereunder or to take any action to collect or
enforce any claim for payment assigned hereunder.

                                   ARTICLE III

                         REPRESENTATIONS AND WARRANTIES

         Pledgor hereby represents and warrants to the  Administrative  Agent as
follows:

         (a) Pledgor has good and indefeasible title to the Pledged  Partnership
Interests  and  other  Collateral  free and  clear of any  Lien  except  for the
Security  Interests created by this Agreement and the security interests granted
in  favor  of  Bank of  America,  N.A.,  as  Administrative  Agent  ("Refractive
Administrative  Agent")  under the Loan  Agreement  dated the date  hereof  (the
"Refractive  Loan  Agreement")  among  Prime  Refractive   Management,   L.L.C.,
Refractive  Administrative Agent, BankBoston,  N.A., as documentation agent, and
the lenders from time to time party thereto ("Refractive Lenders"),  and has all
necessary  authority to pledge and collaterally  assign the Pledged  Partnership
Interests and other Collateral as security for the Secured  Obligations and such
assignment  and transfer is not contrary to or in conflict with the  Partnership
Agreements or any other agreement;

         (b) No  financing  statement  or other  instrument  similar  in  effect
covering all or any part of the  Collateral is on file in any recording  office,
except such as may have been filed in favor of the Administrative Agent relating
to this Agreement or those in favor of Refractive Administrative Agent;

     (c) This  Agreement  has been duly executed and delivered by Pledgor and is
the legal and binding  obligation of Pledgor  enforceable in accordance with its
terms;


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         (d) Upon  execution  of this  Agreement  and an  appropriate  financing
statement  by  Pledgor  and the  recording  of the  financing  statement  in the
appropriate office, the Administrative  Agent will have a valid, first and prior
perfected security interest in the Collateral;

         (e) Neither the  execution  and  delivery  of this  Agreement,  nor the
consummation of any of the transactions hereby contemplated, nor compliance with
the terms and provisions hereof, will contravene or materially conflict with (i)
any material  provision of law,  statute or  regulation  to which Pledgor or the
Partnerships  is  subject  or  (ii)  any  judgment,  license,  order  or  permit
applicable to Pledgor or the Partnerships.  No consent, approval,  authorization
or  order of any  court,  governmental  authority,  partner  or  third  party is
required that has not been received or taken (i) for the grant by Pledgor of the
Security  Interests,  (ii) for the  execution,  delivery or  performance of this
Agreement by Pledgor,  (iii) for the  perfection of the Security  Interests,  or
(iv) except for such notices as are required by the Code or the Loan  Agreement,
for  the  exercise  by the  Administrative  Agent  of its  rights  and  remedies
hereunder (provided,  however,  that the purchaser of the Collateral at any sale
thereof  pursuant to Section 5.4 hereof may be required to obtain the consent of
the partners in the  Partnerships  and/or satisfy other  conditions set forth in
the Partnership  Agreements prior to such purchaser's  admission as a partner in
the Partnership);

     (f) The chief  executive  office and principal place of business of Pledgor
is in Austin, Travis County, Texas; and

         (g) To the best  knowledge  and belief of  Pledgor,  Pledgor  has fully
performed each and every one of his obligations and duties under the Partnership
Agreements  on or prior to the date due;  Pledgor has not received any notice of
any  default  in  the  performance  of his  obligations  under  the  Partnership
Agreements or of any situation which could give rise to such an event of default
thereunder.

                                   ARTICLE IV

                               PLEDGOR'S COVENANTS

         Pledgor hereby covenants and agrees with the Administrative  Agent that
until the Secured Indebtedness is paid and performed in full:

     (a)  Pledgor  will  not  cause,  permit  or  consent  to any  amendment  or
modification  to the  Partnership  Agreements  in effect  as of the date  hereof
except as permitted in the Loan Agreement;

         (b)  Pledgor  will  pay and  discharge  promptly  when  due all  taxes,
assessments,  forced contributions,  governmental charges, fines, penalties, and
any other lawful claims, of every  description,  payable by Pledgor with respect
to (or  which,  if not paid  could  result  in an  encumbrance  upon) any of the
Collateral, except as otherwise permitted by the terms of the Loan Agreement. In
the  event  that  Pledgor  should,  for any  reason,  fail to pay and  discharge
promptly any taxes,  assessments,  forced  contributions,  governmental charges,
fines, or penalties when due (subject to the provisions of the Loan  Agreement),
then the Administrative  Agent shall be authorized,  but shall not be obligated,
to pay the same, with full  subrogation to all rights of any Person by reason of
such  payment,  and the  amounts  so paid,  together  with  interest  thereon as
provided herein, shall be secured by the Security Interests;


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         (c) Pledgor will not sell, transfer, mortgage or otherwise encumber any
Collateral  in any  manner,  except  for  the  security  interest  in  favor  of
Refractive  Administrative Agent, without first obtaining the written consent of
the  Administrative  Agent.  Any  written  consent to any such  sale,  mortgage,
transfer or encumbrance  shall not be construed to be a waiver of this provision
in respect of any subsequent proposed sale, mortgage, transfer or encumbrance;

         (d)  Pledgor  will,  at its  expense and in such manner and form as the
Administrative Agent may from time to time reasonably require, execute, deliver,
file  and  record  any  financing   statement,   specific  assignment  or  other
instruments,  certificates  or  papers  and take any  other  action  that may be
necessary or desirable,  or that the Administrative  Agent may from time to time
reasonably  request,  in order to  create,  preserve,  perfect or  validate  any
Security Interest or to enable the Administrative  Agent to exercise and enforce
its rights  hereunder with respect to any of the Collateral.  In the event,  for
any  reason,  that the law of any  jurisdiction  other  than the  State of Texas
becomes or is applicable to the Collateral,  or any part thereof, Pledgor agrees
to execute and deliver all such instruments and to do all such other things that
may be necessary or  appropriate  to preserve,  protect and enforce the Security
Interests of the Administrative  Agent under the law of such other jurisdiction,
to at least the same extent that the Security Interests would be protected under
the Code. To the extent permitted by applicable law,  Pledgor hereby  authorizes
the  Administrative  Agent  to  execute  and  file,  in the name of  Pledgor  or
otherwise,  Uniform Commercial Code financing statements that the Administrative
Agent in its sole  discretion  may deem  necessary  or  appropriate  to  further
perfect the Security Interests;

         (e) If Pledgor receives,  by virtue of being or having been an owner of
any of the Collateral, any notes, other instruments, options, cash distributions
or any other distribution,  resulting from a Capital Event (hereinafter defined)
Pledgor  shall  receive the same in trust for the benefit of the  Administrative
Agent,  shall immediately  notify the  Administrative  Agent of such receipt and
shall  immediately  take all such actions and execute all such  documents as the
Administrative  Agent deems  necessary or  appropriate  to continue or create as
first and prior perfected Liens, in favor of the  Administrative  Agent covering
such notes, other instruments,  options, cash distributions. As used herein, the
term  "Capital  Event" shall mean any event  generating or resulting in revenues
not attributable to the normal business operations of the Partnerships including
without   limitation,   any  mortgaging  of  assets,   refinancing  of  existing
indebtedness of any Partnership,  condemnation of any assets of any Partnership,
sale or transfer of any assets of any Partnership outside the ordinary course of
business,  or payment of insurance proceeds.  At all times other than during the
continuance  of an Event of Default,  Pledgor  shall be entitled to receive free
from the security  interest  hereof any note,  other  instrument,  option,  cash
distribution  or any other  distribution  resulting  from any event other than a
Capital Event;

         (f) Pledgor will notify the  Administrative  Agent in writing  prior to
the removal of Pledgor's chief  executive  office or principal place of business
from the State of Texas;

         (g) Pledgor shall cause to be obtained any and all waivers and consents
necessary to make  effective the grant  contained in and to perfect the security
interest  granted to the  Administrative  Agent  pursuant to Section 2.1 hereof,
including without limitation,  all necessary waivers and consents from the other
partners, if any, of each Partnership;

         (h) Pledgor shall perform fully all obligations  imposed upon it by any
agreements  or  instruments  concerning  all or  any  part  of  the  Collateral,
including  without  limitation the Partnership  Agreements and shall maintain in
full force and effect all such agreements and  instruments,  and shall not amend
or modify,  or consent to the amendment or  modification  of such  agreements or
instruments, without the prior written consent of the Administrative Agent; and


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         (i)  Pledgor  shall  promptly  notify the  Administrative  Agent of any
material adverse change in any material fact or material circumstance  warranted
or represented by Pledgor in this Agreement or in any other writing furnished by
Pledgor to the  Administrative  Agent in connection  with the  Collateral or the
Secured Indebtedness,  and shall promptly notify the Administrative Agent of any
claim,  action or  proceeding  affecting  title to the  Collateral,  or any part
thereof,  or  the  Security  Interests  herein,  and,  at  the  request  of  the
Administrative  Agent, shall appear and defend, at Pledgor's  expense,  any such
action or proceeding.

                                    ARTICLE V

                    GENERAL AUTHORITY AND POWERS AND REMEDIES

         SECTION 5.1       Events of Default.
                           -----------------

         Pledgor shall be in default under this  Agreement upon the happening of
any of the  following  events  or  conditions  (hereinafter  called an "Event of
Default"):

         (a)      An Event of Default under the Loan Agreement shall occur; or

     (b) The ownership of any of the  Collateral  becomes  vested in a person or
entity other than Pledgor, except as permitted hereunder; or

     (c) The Administrative Agent's Liens in any of the Collateral should become
unenforceable, or cease to be first priority Liens.

         SECTION 5.2 Right to Receive  Distributions.  The Administrative  Agent
shall  have the  right,  at any time  following  the  occurrence  and during the
continuation of an Event of Default,  to receive all payments and  distributions
made to Pledgor upon or with  respect to the  Collateral  and Pledgor  agrees to
take all such action as the  Administrative  Agent may reasonably deem necessary
or appropriate to give effect to such right.

         SECTION 5.3 General Authority.  Pledgor hereby irrevocably appoints the
Administrative  Agent,  and its  successors  and  assigns,  the true and  lawful
attorney-in-fact  of Pledgor,  with full power of  substitution,  in the name of
Pledgor,  for the sole  use and  benefit  of the  Administrative  Agent,  but at
Pledgor's expense,  to the extent permitted by law to exercise,  at any time and
from time to time  following the  occurrence  and during the  continuance  of an
Event of Default,  all or any of the following powers with respect to all or any
of the Collateral:

     (a) to ask,  demand,  sue for,  collect,  receive and give  acquittance and
receipts for any and all monies due or to become due upon or by virtue thereof;

     (b) to  receive,  endorse,  and  collect  any drafts or other  instruments,
documents and chattel paper,
in connection with clause (a) preceding;

     (c) to  settle,  compromise,  compound,  prosecute  or defend any action or
proceeding with respect thereto;



<PAGE>


         (d)  subject  to  Section  5.4  hereof,  to sell,  transfer,  assign or
otherwise  deal in or with  the  same  or the  proceeds  thereof  as  fully  and
effectually as if the Administrative Agent were the absolute owner thereof; and

     (e) to extend  the time of payment  of any or all  thereof  and to make any
allowance and other adjustments with reference thereto.

In addition,  the  Administrative  Agent, at any time, either before or after an
Event of Default, shall have the right, together with such accountants and other
agents or representatives as they may from time to time designate,  to visit and
inspect the Partnerships'  properties,  assets, books, records and documents and
to discuss the Partnerships'  affairs,  finances and accounts with Pledgor's and
the Partnerships'  representatives,  officers or directors,  during all business
hours as the  Administrative  Agent  may  designate,  and to make and take  away
copies of the  Partnerships'  records  at the  Administrative  Agent's  expense.
Pledgor  shall  furnish  to  Administrative  Agent  any  information  reasonably
requested by the Administrative Agent in connection with the Collateral. Pledgor
will maintain complete and accurate books and records regarding the Collateral.

         SECTION 5.4       Remedies Upon Default.
                           ---------------------

         (a) If any Event of Default shall have occurred and is continuing,  the
Administrative  Agent,  at its option,  without demand,  presentment,  notice of
acceleration,  intention to  accelerate or other notice (which are fully waived)
may:

                  (1) exercise all the rights of a secured  party under the Code
         (whether  or not the Code is in effect in the  jurisdiction  where such
         rights are exercise, unless prohibited by applicable law).

               (2) apply the cash, if any, then held by the Administrative Agent
          as Collateral as specified in Section 5.6.

                  (3) sell all of the  Collateral  or any part thereof at public
         or private sale or at any broker's board or on any securities exchange,
         for cash,  upon  credit or for  future  delivery,  and at such price or
         prices as the  Administrative  Agent may reasonably deem  satisfactory.
         Upon the  Administrative  Agent's  demand,  Pledgor will take all steps
         necessary to prepare the  Collateral  for and  otherwise  assist in any
         proposed  disposition  of the  Collateral.  Any  holder of the  Secured
         Indebtedness  may be the  purchaser of any or all of the  Collateral so
         sold at any public sale (or, if the Collateral is of a type customarily
         sold in a  recognized  market or is of a type  which is the  subject of
         widely distributed standard price quotations,  at any private sale) and
         thereafter  hold the same  absolutely,  free from any right or claim of
         whatsoever kind. Any holder of the Secured  Indebtedness shall have the
         right to offset  the amount of its bid  against an equal  amount of the
         Secured Indebtedness held by such holder.


<PAGE>


         Pledgor agrees that, because of the Securities Act of 1933, as amended,
         or any other laws or regulations,  and for other reasons,  there may be
         legal  and/or  practical  restrictions  or  limitations  affecting  the
         Administrative  Agent in any attempts to dispose of certain portions of
         the  Collateral  and for the  enforcement  of their  rights.  For these
         reasons,  the Administrative Agent is hereby authorized by Pledgor, but
         not obligated,  upon the occurrence and during the  continuation  of an
         Event of Default,  to sell all or any part of the Collateral at private
         sale,  subject to  investment  letter or in any other manner which will
         not require the  Collateral,  or any part thereof,  to be registered in
         accordance  with the Securities  Act of 1933, as amended,  or the rules
         and  regulations   promulgated   thereunder,   or  any  other  laws  or
         regulations,  at a  reasonable  price  at such  private  sale or  other
         distribution in the manner  mentioned above.  Pledgor  understands that
         the  Administrative  Agent  may in its  discretion  approach  a limited
         number of potential purchasers and that a sale under such circumstances
         may  yield a lower  price  for the  Collateral,  or any  part or  party
         thereof,  than would  otherwise be obtainable if such  collateral  were
         either  afforded  to  a  larger  number  or  potential  purchasers,  or
         registered or sold in the open market. Pledgor agrees that such private
         sale  shall be deemed to have  been made in a  commercially  reasonable
         manner,  and that the  Administrative  Agent has no obligation to delay
         sale of any  Collateral to permit the issuer thereof to register it for
         public sale under any applicable federal or state securities laws.

         The  Administrative  Agent is authorized,  in connection  with any such
         sale (i) to restrict the prospective bidders on or purchasers of any of
         the Collateral to a limited number of sophisticated  investors who will
         represent and agree that they are  purchasing for their own account for
         investment  and not with a view to the  distribution  or sale of any of
         such Collateral and (ii) to impose such other limitations or conditions
         in connection with any such sale as the Administrative Agent reasonably
         deems  necessary  in order  to  comply  with  applicable  law.  Pledgor
         covenants  and agrees that it will execute and deliver  such  documents
         and take such other action as the Administrative Agent reasonably deems
         necessary  in order that any such sale may be made in  compliance  with
         applicable law. Upon any such sale the Administrative  Agent shall have
         the right to deliver,  assign and transfer to the purchaser thereof the
         Collateral  so sold.  Each  purchaser  at any such sale  shall hold the
         Collateral so sold absolutely,  free from any claim or right of Pledgor
         of  whatsoever  kind,  including  any equity or right of  redemption of
         Pledgor.  Pledgor,  to the extent  permitted by applicable  law, hereby
         specifically  waives all rights of redemption,  stay or appraisal which
         it has or may have under any law now existing or hereafter enacted.

         Pledgor   agrees   that  five  (5)  days'   written   notice  from  the
         Administrative Agent to Pledgor of the Administrative Agent's intention
         to make any such public or private sale or sale at a broker's  board or
         on a securities  exchange shall  constitute  "reasonable  notification"
         within the meaning of Section  9-504(c) of the Code.  Such notice shall
         (1) in case of a public  sale,  state the time and place fixed for such
         sale,  (2) in  case  of sale at a  broker's  board  or on a  securities
         exchange,  state the board or  exchange  at which  such a sale is to be
         made and the day on which the  Collateral,  or the  portion  thereof so
         being sold, will first be offered to sale at such board or exchange and
         (3) in the case of a private sale,  state the day after which such sale
         may be consummated.  Any such public sale shall be held at such time or
         times within ordinary business hours and at such place or places as the
         Administrative  Agent may fix in the notice of such  sale.  At any such
         sale,  the  Collateral  may be  sold in one  lot as an  entirety  or in
         separate parcels, as the Administrative Agent may reasonably determine.
         The  Administrative  Agent shall not be obligated to make any such sale
         pursuant to any such  notice.  The  Administrative  Agent may,  without
         notice or publication,  adjourn any public or private sale or cause the
         same to be adjourned from time to time by  announcement at the time and
         place  fixed  for the  sale,  and such  sale may be made at any time or
         place to which the same may be so adjourned.


<PAGE>


         In case of any sale of all or any part of the  Collateral  on credit or
         for future  delivery,  the  Collateral  so sold may be  retained by the
         Administrative  Agent until the selling  price is paid by the purchaser
         thereof,  but the Administrative Agent shall not incur any liability in
         case  of the  failure  of  such  purchaser  to  take up and pay for the
         Collateral so sold and in case of any such failure, such Collateral may
         again be sold upon like notice.  The Administrative  Agent,  instead of
         exercising the power of sale herein conferred upon it, may proceed by a
         suit or suits at law or in equity to foreclose  the Security  Interests
         and sell the Collateral,  or any portion  thereof,  under a judgment or
         decree of a court or courts of competent jurisdiction.

         (b)  Without  the  limiting  the   foregoing,   or  imposing  upon  the
Administrative  Agent any  obligations or duties not required by applicable law,
Pledgor acknowledges and agrees that, in foreclosing upon any of the Collateral,
or exercising  any other rights or remedies  provided the  Administrative  Agent
hereunder or under applicable law, the  Administrative  Agent may, but shall not
be required to (1) qualify or restrict prospective  purchasers of the Collateral
by requiring evidence of sophistication and/or  creditworthiness,  and requiring
the execution and delivery of confidentiality  agreements or other documents and
agreements as a condition to such prospective purchasers' receipt of information
regarding the Collateral or participation  in any public or private  foreclosure
sale process; (2) provide to prospective  purchasers the Partnership  Agreements
and business and financial information  regarding the Partnerships  available in
the files of the Administrative  Agent at the time of commencing the foreclosure
process,  without the requirement that the Administrative  Agent obtain, or seek
to  obtain,  any  updated  business  or  financial  information  or  Partnership
Agreements, or verify, or certify to prospective purchasers, the accuracy of any
such business or financial  information or Partnership  Agreements;  (3) sell at
foreclosure  all, or a portion but not all, of the rights,  titles and interests
of  Pledgor  in a  particular  Partnership  or group of  Partnerships;  it being
further  specifically  acknowledged  by Pledgor  that  limitations  or potential
limitations  on  the  transfer  of  certain  Collateral  under  the  Partnership
Agreements or other  applicable  agreements or law may limit the  Administrative
Agent's right or ability to foreclose  upon or sell certain  rights,  titles and
interests  of  Pledgor  in the  Partnerships;  (4)  offer  for  sale,  and sell,
partnership  interests  either with, or without,  first  employing an appraiser,
investment  banker, or broker with respect to the evaluation of Collateral,  the
solicitation of purchasers for Collateral, or the manner of sale of Collateral.

         (c) The  Administrative  Agent  shall  have all  rights,  remedies  and
recourse  granted in the Loan Agreement and the other Loan Documents or existing
at common law or equity (including  specifically those granted by the Code), and
such rights and  remedies (1) shall be  cumulative  and  concurrent,  (2) may be
pursued separately,  successively or concurrently  against Pledgor and any party
obligated to pay or perform the Obligations, any of the Collateral, or any other
security  for  any  of  the   Obligations,   at  the  sole   discretion  of  the
Administrative  Agent,  and (3) may be exercised  as often as occasion  therefor
shall arise, it being agreed by Pledgor that the exercise or failure to exercise
any such  rights  or  remedies  shall in no event be  construed  as a waiver  or
release thereof or of any other right, remedy or recourse.

         (d)  Notwithstanding  a  foreclosure  upon  any  of the  Collateral  or
exercise of any other remedy by the  Administrative  Agent in connection with an
Event of Default,  Pledgor shall not be subrogated  thereby to any rights of the
Administrative Agent against the Collateral or any other security for any of the
Obligations.  Pledgor shall not be deemed to be the owner of any interest in any
of  the  Obligations  until  all  of  the  Obligations  have  been  paid  to the
Administrative Agent and are fully performed and discharged.

         (e)  All  recitals  in  any  instrument  of  assignment  or  any  other
instrument executed by the Administrative  Agent incident to the sale, transfer,
assignment or other  disposition  or  utilization  of the Collateral or any part
thereof  hereunder  shall be presumptive  evidence of the matters stated therein
and all  prerequisites  of such sale or other action  contained in such recitals
shall be presumed to have been performed or to have occurred.


<PAGE>


         SECTION  5.5  Waivers  by  Pledgor.  In case of any  Event of  Default,
neither Pledgor nor anyone claiming by, through or under Pledgor,  to the extent
Pledgor  may  lawfully  so  agree,  shall or will set up,  claim or seek to take
advantage of any appraisement,  valuation, stay, extension or redemption law now
or hereafter in force in any locality  where any of the  Collateral  is situated
for purposes of applicable law, in order to prevent or hinder the enforcement of
this  Agreement,  or the  absolute  sale of the  Collateral,  or the  final  and
absolute putting into possession  thereof,  immediately  after such sale, of the
purchaser thereof;  and Pledgor in Pledgor's own right and for all who may claim
under Pledgor, hereby waives, to the fullest extent that Pledgor may lawfully do
so, the benefit of any and all right to have the  Collateral  marshaled upon any
enforcement of the Security  Interests  herein granted,  and Pledgor agrees that
the  Administrative  Agent or any  court  having  jurisdiction  to  enforce  the
Security Interests may sell the Collateral in parts or as an entirety.

         SECTION 5.6  Application of Proceeds.  The  Administrative  Agent shall
apply  the  proceeds  of any  foreclosure  sale or  other  realization  upon the
Collateral  as follows  (as  modified,  if  necessary,  by the  requirements  of
applicable law):

         (a) First,  to the payment of all reasonable  costs and expenses of any
foreclosure   and  collection   hereunder  and  all  proceedings  in  connection
therewith, including reasonable compensation to Administrative Agent's counsel;

         (b) Then,  to the  reimbursement  of the  Administrative  Agent for all
disbursements made by the Administrative  Agent for taxes,  assessments or liens
superior to the Security Interests and which the Administrative Agent shall deem
expedient to pay;

     (c) Then, to the  reimbursement of the  Administrative  Agent for any other
disbursements  made by, or reasonable  expenses incurred by, the  Administrative
Agent in accordance with the terms hereof;

     (d) Then,  to the Secured  Indebtedness,  in any manner  determined  by the
Administrative Agent in its sole discretion;

     (e)  Then,  to  the  Refractive  Administrative  Agent  until  all  secured
obligations of Pledgor to it and Refractive Lenders have been paid; and

     (f)      The remainder of such proceeds, if any, shall be paid to Pledgor.

         The foregoing  application  provisions shall apply not only to proceeds
resulting from foreclosure but also to proceeds or distributions  resulting from
any other claim,  (including claims made in bankruptcy  proceedings),  action or
proceeding  to  enforce  or  protect  the  Administrative  Agent's  lien  in the
Collateral.

         SECTION  5.7  Enforcement  of  Secured  Indebtedness.  Nothing  in this
Agreement  shall affect or impair the  unconditional  and absolute  right of the
Administrative  Agent to enforce the Secured  Indebtedness  as and when the same
shall become due in accordance  with the terms of the Loan Documents  whether by
acceleration or otherwise.


<PAGE>



                                   ARTICLE VI

                                  MISCELLANEOUS

         SECTION 6.1 Terms Commercially Reasonable.  The terms of this Agreement
shall be deemed  commercially  reasonable  within  the  meaning  of the  Uniform
Commercial Code in effect and applicable hereto.

         SECTION 6.2 Headings.  The headings of articles and sections herein are
inserted only for convenience and shall in no way define,  describe or limit the
scope or intent of any provision of this Agreement.

         SECTION   6.3   Amendments.   No   change,   amendment,   modification,
cancellation  or discharge of any  provision  of this  Agreement  shall be valid
unless consented to in writing by the Administrative  Agent and Pledgor (subject
to the terms of the Loan Agreement).

         SECTION  6.4  Assignment  of the  Administrative  Agent's  Rights.  The
Administrative  Agent  shall have the right to assign all or any  portion of its
rights  under  this  Agreement  to  any  subsequent  holder  or  holders  of the
Obligations.

         SECTION  6.5 Parties in  Interest.  As and when used  herein,  the term
"Pledgor"  shall mean and include  Pledgor  herein named and his  successors and
permitted assigns,  and the term  "Administrative  Agent" shall mean and include
the  Administrative  Agent herein named and his successors and assigns,  and all
covenants and  agreements  herein shall be binding upon and inure to the benefit
of Pledgor and the Administrative  Agent and their respective assigns,  provided
that  Pledgor  shall have no right to assign his rights  hereunder  to any other
Person  except  in  connection  with  a  transfer  of the  Collateral  permitted
hereunder.

         SECTION  6.6  APPLICABLE  LAWS.  THIS  AGREEMENT  SHALL  BE  CONSTRUED,
INTERPRETED  AND  ENFORCED  UNDER AND PURSUANT TO THE LAWS OF THE STATE OF TEXAS
AND  APPLICABLE  FEDERAL LAW. IF ANY  PROVISION OF THIS  AGREEMENT IS HELD TO BE
INVALID  OR  UNENFORCEABLE,   THE  VALIDITY  AND  ENFORCEABILITY  OF  THE  OTHER
PROVISIONS OF THIS AGREEMENT SHALL REMAIN UNAFFECTED.

         SECTION 6.7 Notices.  Any notices or other  communications  required or
permitted to be given by this Agreement or any other  documents and  instruments
referred  to herein  must be given in  accordance  with  Section  11 of the Loan
Agreement, to the address of such party as follows:

   If to the Administrative Agent:
                                  515 Congress Avenue, 11th Floor
                                  Austin, Texas 78701
                                  Attn: Wade Morgan

                    If to Pledgor:
                                  1301 Capital of Texas Highway
                                  Suite C-300
                                  Austin, Texas 78746-6550
                                  Attn: Treasurer


<PAGE>


         SECTION 6.8  Financing  Statement.  The  Administrative  Agent shall be
entitled  at any  time to file a  photographic  or  other  reproduction  of this
Agreement as a financing statement,  but the failure of the Administrative Agent
to do so shall not impair the validity or enforceability of this Agreement.

         SECTION  6.9  Obligations  Absolute.  All  rights and  remedies  of the
Administrative  Agent hereunder,  and all obligations of the Pledgor  hereunder,
shall be absolute and unconditional irrespective of:

          (a) any lack of validity or  enforceability  of the Loan  Agreement or
     any of the other  Loan  Documents  or any  other  agreement  or  instrument
     relating to any of the foregoing;

          (b) any change in the time,  manner, or place of payment of, or in any
     other term of, all or any of the  Obligations,  or any other  amendment  or
     waiver of or any consent to any departure from the Loan Agreement or any of
     the other Loan Documents;

          (c) any exchange,  release, or nonperfection of any Collateral, or any
     release or  amendment  or waiver of or consent  to any  departure  from any
     guarantee, for all or any of the Obligations; or

                  (d) any other circumstance  (other than payment in full of the
         Obligations) that might otherwise constitute a defense available to, or
         a discharge of, Pledgor.

         SECTION 6.10  Confirmation  of Liens.  Pledgor  acknowledges  that this
Agreement has been given in amendment, renewal, restatement, and confirmation of
Pledgor's  obligations,  covenants,  and agreements  contained in the Pledge and
Security  Agreements  previously  executed by Pledgor in favor of Administrative
Agent and the Lenders, including,  without limitation, that dated April 26, 1996
(the "Previous  Pledge").  Pledgor further  confirms and agrees that neither the
execution of the Loan Agreement or any other Loan Document,  or the consummation
of the transactions described therein, shall in any way affect the liens granted
under the  Previous  Pledge  or the  perfection  or  priority  thereof,  and the
obligations  evidenced by the Previous  Pledge shall  continue in full force and
effect as modified, amended and restated by the terms contained herein.

         SECTION 6.11  Counterparts.  This Agreement may be executed in multiple
counterparts,  each of which shall be deemed to be an original, but all of which
shall  constitute  one and the  same  instrument,  and in  making  proof of this
Agreement it shall not be necessary to produce or account for more than one such
counterpart.


<PAGE>


         SECTION  6.12 ENTIRE  AGREEMENT.  THIS  AGREEMENT  EMBODIES  THE FINAL,
ENTIRE  AGREEMENT  OF  PLEDGOR,  THE  AGENTS  AND THE  LENDERS  WITH  RESPECT TO
PLEDGOR'S PLEDGE OF THE PLEDGED  PARTNERSHIP  INTERESTS AND RESTATES ANY AND ALL
PRIOR COMMITMENTS,  AGREEMENTS,  REPRESENTATIONS,  AND  UNDERSTANDINGS,  WHETHER
WRITTEN OR ORAL,  RELATING TO THE  SUBJECT  MATTER  HEREOF.  THIS  AGREEMENT  IS
INTENDED  BY  PLEDGOR,  THE  AGENTS  AND THE  LENDERS  AS A FINAL  AND  COMPLETE
EXPRESSION  OF THE TERMS OF THIS  AGREEMENT,  AND NO COURSE OF  DEALING  BETWEEN
PLEDGOR,  THE  AGENTS  OR THE  LENDERS,  NO  COURSE  OF  PERFORMANCE,  NO  TRADE
PRACTICES,  AND  NO  EVIDENCE  OF  PRIOR,  CONTEMPORANEOUS  OR  SUBSEQUENT  ORAL
AGREEMENTS OR  DISCUSSIONS  OR OTHER  EXTRINSIC  EVIDENCE OF ANY NATURE SHALL BE
USED TO CONTRADICT, VARY, SUPPLEMENT OR MODIFY ANY TERM OF THIS AGREEMENT. THERE
ARE NO ORAL AGREEMENTS AMONG PLEDGOR, THE AGENTS AND THE LENDERS.

                     [REMAINDER OF PAGE INTENTIONALLY BLANK.

                            SIGNATURE PAGES FOLLOW.]


<PAGE>



                                                   Pledge and Security Agreement

         IN WITNESS  WHEREOF,  Pledgor has executed this Agreement as of the day
and year first above written.

                                    PLEDGOR:

                                                     OHIO LITHO, INC.,
                                                       a Delaware corporation

                                                     By: /s/ Teena E. Belcik
                                                              Teena E. Belcik
                                                              Treasurer


<PAGE>



                                                                       Exhibit A



                                    EXHIBIT A

                                  PARTNERSHIPS

Ohio Mobile Lithotripter, Ltd.

Ohio Mobile Lithotripter II, Ltd.





<PAGE>



                                                                       Exhibit B



                                    EXHIBIT B

                             PARTNERSHIP AGREEMENTS

First  Amended and  Restated  Agreement  of Limited  Partnership  of Ohio Mobile
Lithotripter,  Ltd. dated August 1, 1991, as amended by First Amendment to First
Amended and Restated  Agreement of Limited  Partnership dated as of December 31,
1992

Certificate of Limited Partnership of Ohio Mobile  Lithotripter,  Ltd. dated May
21, 1991

First  Amended and  Restated  Agreement  of Limited  Partnership  of Ohio Mobile
Lithotripter II, Ltd.

Certificate of Limited  Partnership of Ohio Mobile  Lithotripter  II, Ltd. dated
August 23, 1995




                          Pledge and Security Agreement



                          PLEDGE AND SECURITY AGREEMENT

         THIS  PLEDGE  AND  SECURITY  AGREEMENT  (the  "Agreement")  dated as of
January 31,  2000,  is by and between OHIO LITHO,  INC., a Delaware  corporation
("Pledgor"), whose street address is 1301 Capital of Texas Highway, Suite C-300,
Austin, Texas 78746-6550,  for the benefit of BANK OF AMERICA,  N.A., a national
banking association ("B of A"), whose street address is 901 Main Street, Dallas,
Texas 75202, not in its individual  capacity but solely as administrative  agent
for itself and each of the other banks or lending institutions (each, a "Lender"
and collectively, the "Lender") which is or may from time to time become a party
to the Loan Agreement (as hereinbelow defined) (in such capacity,  together with
its successors in such capacity, the "Administrative Agent").

                                R E C I T A L S:

     A.  Prime  Refractive  Management,  L.L.C.,  a Delaware  limited  liability
company  ("Borrower"),  has entered into that certain Loan Agreement dated as of
the date hereof with B of A as Administrative Agent and as a Lender, BankBoston,
N.A., as Documentation Agent and as a Lender, and the other Lenders from time to
time party thereto, as amended,  waived, restated, and supplemented from time to
time ("Loan Agreement").

         B. Pledgor and certain  other  guarantors  have  executed  that certain
Guaranty  Agreement  dated as of the date  hereof  (as the same may be  amended,
supplemented or modified from time to time, the  "Guaranty"),  pursuant to which
Pledgor has guaranteed to the Agents (as defined in the Loan  Agreement) and the
Lenders  the full and  complete  payment  and  performance  of the  liabilities,
obligations,  and  indebtedness  of the  Borrower  to the Agents and the Lenders
under the Loan Documents (as defined in the Loan Agreement).

     C. As a condition to entering into the Loan Agreement, Pledgor must execute
and deliver this Agreement.

         NOW  THEREFORE,  in  consideration  of the  premises and other good and
valuable  consideration,  the  receipt  and  sufficiency  of  which  are  hereby
acknowledged, Pledgor agrees with the Administrative Agent as follows:

                                    ARTICLE I

                                   DEFINITIONS

         (a) Each term used herein and defined in the Loan Agreement  shall have
the  meaning  assigned to it in the Loan  Agreement,  unless  otherwise  defined
herein or the context otherwise requires.

         (b) In addition,  as used herein,  the  following  terms shall,  unless
otherwise indicated, have the following meanings:

         "Borrower" has the meaning set forth in the recitals.

         "Code" shall mean the Uniform Commercial Code as in effect in the State
of Texas.

         "Collateral"  shall mean the assets and interests of Pledgor identified
in Section 2.1 hereof.


<PAGE>



                          Pledge and Security Agreement

                                       12



         "Event of  Default"  shall have the  meaning  assigned  to such term in
Section 5.1.

         "Guaranty" shall mean that certain  Guaranty  Agreement dated as of the
date hereof, executed by Pledgor and certain other guarantors for the benefit of
the Agents and the Lenders, guaranteeing the full payment and performance of the
Obligations, as amended, modified, confirmed, and extended from time to time.

         "Partnerships"  shall mean (a) those partnerships and limited liability
companies  listed on  Exhibit  A  attached  hereto  and  incorporated  herein by
reference,  as such  partnerships  or limited  liability  companies exist or may
hereinafter be restated,  amended or restructured,  (b) any  partnership,  joint
venture,  or limited  liability  company in which  Pledgor  shall,  at any time,
become  a  limited  or  general  partner,   venturer,  or  member,  or  (c)  any
partnership, joint venture or corporation formed as a result of the restructure,
reorganization or amendment of the Partnerships.

         "Partnership  Agreements"  shall  mean (a) those  agreements  listed on
Exhibit B attached hereto and  incorporated  herein by reference  (together with
any  modifications,  amendments or  restatements  thereof),  and (b) partnership
agreements,  joint venture agreements,  or organizational  agreements for any of
the partnerships,  joint ventures,  or limited liability  companies described in
clause  (b) of  the  definition  of  "Partnerships"  above  (together  with  any
modifications,  amendments or restatements thereof), and "Partnership Agreement"
means any one of the Partnership Agreements.

         "Pledged Partnership Interests" shall mean all of Pledgor's partnership
interests,  whether general or limited, venture, or membership interests, in the
Partnerships,  including,  without limitation, all of Pledgor's right, title and
interest now or hereafter accruing under the Partnership Agreements with respect
to any  interest  now owned or  hereafter  acquired  or owned by  Pledgor in the
Partnerships,  and including all  distributions,  allocations,  proceeds,  fees,
preferences,  payments or other benefits,  which Pledgor now is or may hereafter
become  entitled to receive with respect to such  interests in the  Partnerships
and with respect to the repayment of all loans now or hereafter  made by Pledgor
to the Partnerships,  and Pledgor's undivided  percentage interest in the assets
of the Partnerships.

         "Secured  Indebtedness" shall have the meaning assigned to such term in
Section 2.1(c) hereof.

         "Security Interests" shall mean the pledge, collateral assignment,  and
security interests securing the Secured  Indebtedness,  including (i) the pledge
and  security  interest in the  Pledged  Partnership  Interests  granted in this
Agreement  and  (ii)  all  other  security  interests  created  or  assigned  as
additional security for the Secured  Indebtedness  pursuant to the provisions of
this Agreement.

         (c) Whenever the context so requires,  the neuter  gender  includes the
masculine and  feminine,  and the singular  number  includes the plural and vice
versa.


<PAGE>


                                   ARTICLE II

                            COLLATERAL AND OBLIGATION

         SECTION 2.1       Grant of Security Interest.
                           --------------------------

         (a) As collateral  security for Secured  Indebtedness,  Pledgor  hereby
pledges and grants to the Administrative  Agent, for the benefit of the Lenders,
a lien on and security  interest in and to, and agrees and acknowledges that the
Administrative Agent has, and shall continue to have, a security interest in and
to, and assigns, transfers, pledges and conveys to the Administrative Agent, all
of  Pledgor's  right,  title  and  interest  in and to the  following  described
collateral (the "Collateral") now owned or hereafter acquired, wherever located,
howsoever  arising or created,  and whether now existing or  hereafter  arising,
existing or created,  subject to a first lien in favor of Bank of America, N.A.,
as Administrative Agent ("Prime  Administrative Agent") under the Fourth Amended
and Restated Loan Agreement  dated the date hereof (the "Prime Loan  Agreement")
among Prime Medical  Services,  Inc., Prime  Administrative  Agent,  BankBoston,
N.A., as  documentation  agent,  and the lenders ("Prime  Lenders") from time to
time thereunder:

                    (i)  the  Pledged  Partnership  Interests  and all rights of
                         Pledgor with respect  thereto and all proceeds,  income
                         and profits therefrom;


                  (ii)     all of Pledgor's  distribution rights, income rights,
                           liquidation  interest,   accounts,  contract  rights,
                           general intangibles,  notes, instruments,  drafts and
                           documents   relating  to  the   Pledged   Partnership
                           Interests;

                  (iii)    to the extent attributable to the Pledged Partnership
                           Interests,  all promissory  notes,  notes receivable,
                           accounts,  accounts  receivable and instruments owned
                           or held by Pledgor or, in which Pledgor owns or holds
                           an   interest,    evidencing   obligations   of   the
                           Partnerships;

                  (iv)     all liens, security interests,  collateral,  property
                           and  assets  securing  any of the  promissory  notes,
                           notes receivables,  instruments,  accounts receivable
                           and other  claims and  interest  described  in clause
                           (iii) above;

                    (v)  all books, files, computer records,  computer software,
                         electronic  information  and other  files,  records  or
                         information  relating  to any or all of the  foregoing;
                         and

                  (vi)     all substitutions,  replacements, products, proceeds,
                           income and profits arising from any of the foregoing;
                           including without limitation insurance proceeds.

         (b)  The  Security   Interests  are  granted  and  the   Collateral  is
collaterally  assigned as security only and shall not subject the Administrative
Agent or any holder of the  Secured  Indebtedness  to, or transfer or in any way
affect or modify,  any obligation or liability of Pledgor with respect to any of
the Collateral.

         (c)  The   Collateral   shall   secure   the   following   obligations,
indebtedness,  and liabilities  (whether at stated maturity,  by acceleration or
otherwise)  (all  such   obligations,   indebtedness,   and  liabilities   being
hereinafter sometimes called the "Secured Indebtedness"):


<PAGE>


                    (i)  the  Obligations and the  obligations,  liabilities and
                         indebtedness  of Pledgor to the Agents and the  Lenders
                         under the Guaranty;

                  (ii)     all reasonable costs and expenses, including, without
                           limitation,  all reasonable attorneys' fees and legal
                           expenses, incurred by any of the Agents or any Lender
                           to preserve and maintain the Collateral,  collect the
                           obligations   herein  described,   and  enforce  this
                           Agreement; and

                    (iii)all extensions,  renewals,  and modifications of any of
                         the foregoing.

         SECTION 2.2 Consent.  To the extent any Partnership  Agreement requires
the consent or agreement of Pledgor to the transfer,  conveyance, or encumbrance
as security  for the Secured  Indebtedness  of all or any portion of the Pledged
Partnership  Interests,  Pledgor hereby irrevocably consents to (a) the grant of
the security  interest  described in Section 2.1 of this Agreement,  and (b) any
transfer or  conveyance  of the Pledged  Partnership  Interests  pursuant to the
Administrative  Agent's exercise of its rights and remedies under Section 5.4 of
this Agreement or under any other Loan Document.

         SECTION 2.3 Pledgor  Remains  Liable.  Notwithstanding  anything to the
contrary contained herein, (a) Pledgor shall remain liable under the Partnership
Agreements  to the  extent set forth  therein  to perform  all of its duties and
obligations  thereunder  to the same  extent as if this  Agreement  had not been
executed  (b) the  exercise  by the  Administrative  Agent of any of its  rights
hereunder shall not release Pledgor from any of its duties or obligations  under
the contracts and  agreements  included in the  Collateral,  and (c) neither the
Administrative Agent nor any Lender shall have any obligation or liability under
the  Partnership  Agreements  by  reason  of  this  Agreement,   nor  shall  the
Administrative  Agent  or  any  Lender  be  obligated  to  perform  any  of  the
obligations or duties of Pledgor  thereunder or to take any action to collect or
enforce any claim for payment assigned hereunder.

                                   ARTICLE III

                         REPRESENTATIONS AND WARRANTIES

         Pledgor hereby represents and warrants to the  Administrative  Agent as
follows:

         (a) Pledgor has good and indefeasible title to the Pledged  Partnership
Interests  and  other  Collateral  free and  clear of any  Lien  except  for the
Security  Interests created by this Agreement and the security interests granted
in favor of Prime  Administrative  Agent,  and has all  necessary  authority  to
pledge and  collaterally  assign the  Pledged  Partnership  Interests  and other
Collateral  as security  for the Secured  Obligations  and such  assignment  and
transfer is not contrary to or in conflict  with the  Partnership  Agreements or
any other agreement;

         (b) No  financing  statement  or other  instrument  similar  in  effect
covering all or any part of the  Collateral is on file in any recording  office,
except such as may have been filed in favor of the Administrative Agent relating
to this Agreement or those in favor of Prime Administrative Agent;

     (c) This  Agreement  has been duly executed and delivered by Pledgor and is
the legal and binding  obligation of Pledgor  enforceable in accordance with its
terms;



<PAGE>


         (d) Upon  execution  of this  Agreement  and an  appropriate  financing
statement  by  Pledgor  and the  recording  of the  financing  statement  in the
appropriate  office,  the  Administrative  Agent  will  have a valid,  perfected
security  interest in the  Collateral,  subject  only to the prior lien of Prime
Administrative Agent;

         (e) Neither the  execution  and  delivery  of this  Agreement,  nor the
consummation of any of the transactions hereby contemplated, nor compliance with
the terms and provisions hereof, will contravene or materially conflict with (i)
any material  provision of law,  statute or  regulation  to which Pledgor or the
Partnerships  is  subject  or  (ii)  any  judgment,  license,  order  or  permit
applicable to Pledgor or the Partnerships.  No consent, approval,  authorization
or  order of any  court,  governmental  authority,  partner  or  third  party is
required that has not been received or taken (i) for the grant by Pledgor of the
Security  Interests,  (ii) for the  execution,  delivery or  performance of this
Agreement by Pledgor,  (iii) for the  perfection of the Security  Interests,  or
(iv) except for such notices as are required by the Code or the Loan  Agreement,
for  the  exercise  by the  Administrative  Agent  of its  rights  and  remedies
hereunder (provided,  however,  that the purchaser of the Collateral at any sale
thereof  pursuant to Section 5.4 hereof may be required to obtain the consent of
the partners in the  Partnerships  and/or satisfy other  conditions set forth in
the Partnership  Agreements prior to such purchaser's  admission as a partner in
the Partnership);

     (f) The chief  executive  office and principal place of business of Pledgor
is in Austin, Travis County, Texas; and

         (g) To the best  knowledge  and belief of  Pledgor,  Pledgor  has fully
performed each and every one of his obligations and duties under the Partnership
Agreements  on or prior to the date due;  Pledgor has not received any notice of
any  default  in  the  performance  of his  obligations  under  the  Partnership
Agreements or of any situation which could give rise to such an event of default
thereunder.

                                   ARTICLE IV

                               PLEDGOR'S COVENANTS

         Pledgor hereby covenants and agrees with the Administrative  Agent that
until the Secured Indebtedness is paid and performed in full:

         (a)  Pledgor  will not cause,  permit or consent  to any  amendment  or
modification  to the  Partnership  Agreements  in effect  as of the date  hereof
except as permitted in the Prime Loan Agreement;

         (b)  Pledgor  will  pay and  discharge  promptly  when  due all  taxes,
assessments,  forced contributions,  governmental charges, fines, penalties, and
any other lawful claims, of every  description,  payable by Pledgor with respect
to (or  which,  if not paid  could  result  in an  encumbrance  upon) any of the
Collateral, except as otherwise permitted by the terms of the Loan Agreement. In
the  event  that  Pledgor  should,  for any  reason,  fail to pay and  discharge
promptly any taxes,  assessments,  forced  contributions,  governmental charges,
fines,  or  penalties  when due  (subject  to the  provisions  of the Prime Loan
Agreement),  then the Administrative Agent shall be authorized, but shall not be
obligated, to pay the same, with full subrogation to all rights of any Person by
reason of such payment,  and the amounts so paid, together with interest thereon
as provided herein, shall be secured by the Security Interests;


<PAGE>


         (c) Pledgor will not sell, transfer, mortgage or otherwise encumber any
Collateral  in any manner,  except for the  security  interest in favor of Prime
Administrative  Agent,  without  first  obtaining  the  written  consent  of the
Administrative  Agent. Any written consent to any such sale, mortgage,  transfer
or  encumbrance  shall  not be  construed  to be a waiver of this  provision  in
respect of any subsequent proposed sale, mortgage, transfer or encumbrance;

         (d)  Pledgor  will,  at its  expense and in such manner and form as the
Administrative Agent may from time to time reasonably require, execute, deliver,
file  and  record  any  financing   statement,   specific  assignment  or  other
instruments,  certificates  or  papers  and take any  other  action  that may be
necessary or desirable,  or that the Administrative  Agent may from time to time
reasonably  request,  in order to  create,  preserve,  perfect or  validate  any
Security Interest or to enable the Administrative  Agent to exercise and enforce
its rights  hereunder with respect to any of the Collateral.  In the event,  for
any  reason,  that the law of any  jurisdiction  other  than the  State of Texas
becomes or is applicable to the Collateral,  or any part thereof, Pledgor agrees
to execute and deliver all such instruments and to do all such other things that
may be necessary or  appropriate  to preserve,  protect and enforce the Security
Interests of the Administrative  Agent under the law of such other jurisdiction,
to at least the same extent that the Security Interests would be protected under
the Code. To the extent permitted by applicable law,  Pledgor hereby  authorizes
the  Administrative  Agent  to  execute  and  file,  in the name of  Pledgor  or
otherwise,  Uniform Commercial Code financing statements that the Administrative
Agent in its sole  discretion  may deem  necessary  or  appropriate  to  further
perfect the Security Interests;

         (e) If Pledgor receives,  by virtue of being or having been an owner of
any of the Collateral, any notes, other instruments, options, cash distributions
or any other distribution,  resulting from a Capital Event (hereinafter defined)
Pledgor  shall  receive the same in trust for the benefit of the  Administrative
Agent,  shall immediately  notify the  Administrative  Agent of such receipt and
shall  immediately  take all such actions and execute all such  documents as the
Administrative  Agent deems  necessary or  appropriate  to continue or create as
perfected Liens, in favor of the Administrative Agent covering such notes, other
instruments, options, cash distributions, subject ony to the prior lien in favor
of the Prime  Administrative  Agent.  As used herein,  the term "Capital  Event"
shall mean any event generating or resulting in revenues not attributable to the
normal business operations of the Partnerships including without limitation, any
mortgaging of assets,  refinancing of existing  indebtedness of any Partnership,
condemnation of any assets of any Partnership, sale or transfer of any assets of
any Partnership outside the ordinary course of business, or payment of insurance
proceeds. At all times other than during the continuance of an Event of Default,
Pledgor shall be entitled to receive free from the security  interest hereof any
note, other  instrument,  option,  cash  distribution or any other  distribution
resulting from any event other than a Capital Event;

         (f) Pledgor will notify the  Administrative  Agent in writing  prior to
the removal of Pledgor's chief  executive  office or principal place of business
from the State of Texas;

         (g) Pledgor shall cause to be obtained any and all waivers and consents
necessary to make  effective the grant  contained in and to perfect the security
interest  granted to the  Administrative  Agent  pursuant to Section 2.1 hereof,
including without limitation,  all necessary waivers and consents from the other
partners, if any, of each Partnership;

         (h) Pledgor shall perform fully all obligations  imposed upon it by any
agreements  or  instruments  concerning  all or  any  part  of  the  Collateral,
including  without  limitation the Partnership  Agreements and shall maintain in
full force and effect all such agreements and  instruments,  and shall not amend
or modify,  or consent to the amendment or  modification  of such  agreements or
instruments, without the prior written consent of the Administrative Agent; and


<PAGE>


         (i)  Pledgor  shall  promptly  notify the  Administrative  Agent of any
material adverse change in any material fact or material circumstance  warranted
or represented by Pledgor in this Agreement or in any other writing furnished by
Pledgor to the  Administrative  Agent in connection  with the  Collateral or the
Secured Indebtedness,  and shall promptly notify the Administrative Agent of any
claim,  action or  proceeding  affecting  title to the  Collateral,  or any part
thereof,  or  the  Security  Interests  herein,  and,  at  the  request  of  the
Administrative  Agent, shall appear and defend, at Pledgor's  expense,  any such
action or proceeding.

                                    ARTICLE V

                    GENERAL AUTHORITY AND POWERS AND REMEDIES

         SECTION 5.1       Events of Default.
                           -----------------

         Pledgor shall be in default under this  Agreement upon the happening of
any of the  following  events  or  conditions  (hereinafter  called an "Event of
Default"):

         (a)      An Event of Default under the Loan Agreement shall occur; or

     (b) The ownership of any of the  Collateral  becomes  vested in a person or
entity other than Pledgor, except as permitted hereunder; or

         (c) The  Administrative  Agent's Liens in any of the Collateral  should
become  unenforceable,  or cease to be first priority Liens, subject only to the
prior lien of Prime Administrative Agent.

         SECTION 5.2 Right to Receive  Distributions.  The Administrative  Agent
shall  have the  right,  at any time  following  the  occurrence  and during the
continuation of an Event of Default,  to receive all payments and  distributions
made to Pledgor upon or with  respect to the  Collateral  and Pledgor  agrees to
take all such action as the  Administrative  Agent may reasonably deem necessary
or appropriate to give effect to such right.

         SECTION 5.3 General Authority.  Pledgor hereby irrevocably appoints the
Administrative  Agent,  and its  successors  and  assigns,  the true and  lawful
attorney-in-fact  of Pledgor,  with full power of  substitution,  in the name of
Pledgor,  for the sole  use and  benefit  of the  Administrative  Agent,  but at
Pledgor's expense,  to the extent permitted by law to exercise,  at any time and
from time to time  following the  occurrence  and during the  continuance  of an
Event of Default,  all or any of the following powers with respect to all or any
of the Collateral:

     (a) to ask,  demand,  sue for,  collect,  receive and give  acquittance and
receipts for any and all monies due or to become due upon or by virtue thereof;

     (b) to  receive,  endorse,  and  collect  any drafts or other  instruments,
documents and chattel paper, in connection with clause (a) preceding;

     (c) to  settle,  compromise,  compound,  prosecute  or defend any action or
proceeding with respect thereto;

         (d)  subject  to  Section  5.4  hereof,  to sell,  transfer,  assign or
otherwise  deal in or with  the  same  or the  proceeds  thereof  as  fully  and
effectually as if the Administrative Agent were the absolute owner thereof; and


<PAGE>


     (e) to extend  the time of payment  of any or all  thereof  and to make any
allowance and other adjustments with reference thereto.

In addition,  the  Administrative  Agent, at any time, either before or after an
Event of Default, shall have the right, together with such accountants and other
agents or representatives as they may from time to time designate,  to visit and
inspect the Partnerships'  properties,  assets, books, records and documents and
to discuss the Partnerships'  affairs,  finances and accounts with Pledgor's and
the Partnerships'  representatives,  officers or directors,  during all business
hours as the  Administrative  Agent  may  designate,  and to make and take  away
copies of the  Partnerships'  records  at the  Administrative  Agent's  expense.
Pledgor  shall  furnish  to  Administrative  Agent  any  information  reasonably
requested by the Administrative Agent in connection with the Collateral. Pledgor
will maintain complete and accurate books and records regarding the Collateral.

         SECTION 5.4       Remedies Upon Default.
                           ---------------------

         (a) If any Event of Default shall have occurred and is continuing,  the
Administrative  Agent,  at its option,  without demand,  presentment,  notice of
acceleration,  intention to  accelerate or other notice (which are fully waived)
may:

                  (1) exercise all the rights of a secured  party under the Code
         (whether  or not the Code is in effect in the  jurisdiction  where such
         rights are exercise, unless prohibited by applicable law).

     (2) apply  the  cash,  if any,  then  held by the  Administrative  Agent as
Collateral as specified in Section 5.6.

                  (3) sell all of the  Collateral  or any part thereof at public
         or private sale or at any broker's board or on any securities exchange,
         for cash,  upon  credit or for  future  delivery,  and at such price or
         prices as the  Administrative  Agent may reasonably deem  satisfactory.
         Upon the  Administrative  Agent's  demand,  Pledgor will take all steps
         necessary to prepare the  Collateral  for and  otherwise  assist in any
         proposed  disposition  of the  Collateral.  Any  holder of the  Secured
         Indebtedness  may be the  purchaser of any or all of the  Collateral so
         sold at any public sale (or, if the Collateral is of a type customarily
         sold in a  recognized  market or is of a type  which is the  subject of
         widely distributed standard price quotations,  at any private sale) and
         thereafter  hold the same  absolutely,  free from any right or claim of
         whatsoever kind. Any holder of the Secured  Indebtedness shall have the
         right to offset  the amount of its bid  against an equal  amount of the
         Secured Indebtedness held by such holder.


<PAGE>


         Pledgor agrees that, because of the Securities Act of 1933, as amended,
         or any other laws or regulations,  and for other reasons,  there may be
         legal  and/or  practical  restrictions  or  limitations  affecting  the
         Administrative  Agent in any attempts to dispose of certain portions of
         the  Collateral  and for the  enforcement  of their  rights.  For these
         reasons,  the Administrative Agent is hereby authorized by Pledgor, but
         not obligated,  upon the occurrence and during the  continuation  of an
         Event of Default,  to sell all or any part of the Collateral at private
         sale,  subject to  investment  letter or in any other manner which will
         not require the  Collateral,  or any part thereof,  to be registered in
         accordance  with the Securities  Act of 1933, as amended,  or the rules
         and  regulations   promulgated   thereunder,   or  any  other  laws  or
         regulations,  at a  reasonable  price  at such  private  sale or  other
         distribution in the manner  mentioned above.  Pledgor  understands that
         the  Administrative  Agent  may in its  discretion  approach  a limited
         number of potential purchasers and that a sale under such circumstances
         may  yield a lower  price  for the  Collateral,  or any  part or  party
         thereof,  than would  otherwise be obtainable if such  collateral  were
         either  afforded  to  a  larger  number  or  potential  purchasers,  or
         registered or sold in the open market. Pledgor agrees that such private
         sale  shall be deemed to have  been made in a  commercially  reasonable
         manner,  and that the  Administrative  Agent has no obligation to delay
         sale of any  Collateral to permit the issuer thereof to register it for
         public sale under any applicable federal or state securities laws.

         The  Administrative  Agent is authorized,  in connection  with any such
         sale (i) to restrict the prospective bidders on or purchasers of any of
         the Collateral to a limited number of sophisticated  investors who will
         represent and agree that they are  purchasing for their own account for
         investment  and not with a view to the  distribution  or sale of any of
         such Collateral and (ii) to impose such other limitations or conditions
         in connection with any such sale as the Administrative Agent reasonably
         deems  necessary  in order  to  comply  with  applicable  law.  Pledgor
         covenants  and agrees that it will execute and deliver  such  documents
         and take such other action as the Administrative Agent reasonably deems
         necessary  in order that any such sale may be made in  compliance  with
         applicable law. Upon any such sale the Administrative  Agent shall have
         the right to deliver,  assign and transfer to the purchaser thereof the
         Collateral  so sold.  Each  purchaser  at any such sale  shall hold the
         Collateral so sold absolutely,  free from any claim or right of Pledgor
         of  whatsoever  kind,  including  any equity or right of  redemption of
         Pledgor.  Pledgor,  to the extent  permitted by applicable  law, hereby
         specifically  waives all rights of redemption,  stay or appraisal which
         it has or may have under any law now existing or hereafter enacted.

         Pledgor   agrees   that  five  (5)  days'   written   notice  from  the
         Administrative Agent to Pledgor of the Administrative Agent's intention
         to make any such public or private sale or sale at a broker's  board or
         on a securities  exchange shall  constitute  "reasonable  notification"
         within the meaning of Section  9-504(c) of the Code.  Such notice shall
         (1) in case of a public  sale,  state the time and place fixed for such
         sale,  (2) in  case  of sale at a  broker's  board  or on a  securities
         exchange,  state the board or  exchange  at which  such a sale is to be
         made and the day on which the  Collateral,  or the  portion  thereof so
         being sold, will first be offered to sale at such board or exchange and
         (3) in the case of a private sale,  state the day after which such sale
         may be consummated.  Any such public sale shall be held at such time or
         times within ordinary business hours and at such place or places as the
         Administrative  Agent may fix in the notice of such  sale.  At any such
         sale,  the  Collateral  may be  sold in one  lot as an  entirety  or in
         separate parcels, as the Administrative Agent may reasonably determine.
         The  Administrative  Agent shall not be obligated to make any such sale
         pursuant to any such  notice.  The  Administrative  Agent may,  without
         notice or publication,  adjourn any public or private sale or cause the
         same to be adjourned from time to time by  announcement at the time and
         place  fixed  for the  sale,  and such  sale may be made at any time or
         place to which the same may be so adjourned.

         In case of any sale of all or any part of the  Collateral  on credit or
         for future  delivery,  the  Collateral  so sold may be  retained by the
         Administrative  Agent until the selling  price is paid by the purchaser
         thereof,  but the Administrative Agent shall not incur any liability in
         case  of the  failure  of  such  purchaser  to  take up and pay for the
         Collateral so sold and in case of any such failure, such Collateral may
         again be sold upon like notice.  The Administrative  Agent,  instead of
         exercising the power of sale herein conferred upon it, may proceed by a
         suit or suits at law or in equity to foreclose  the Security  Interests
         and sell the Collateral,  or any portion  thereof,  under a judgment or
         decree of a court or courts of competent jurisdiction.


<PAGE>


         (b)  Without  the  limiting  the   foregoing,   or  imposing  upon  the
Administrative  Agent any  obligations or duties not required by applicable law,
Pledgor acknowledges and agrees that, in foreclosing upon any of the Collateral,
or exercising  any other rights or remedies  provided the  Administrative  Agent
hereunder or under applicable law, the  Administrative  Agent may, but shall not
be required to (1) qualify or restrict prospective  purchasers of the Collateral
by requiring evidence of sophistication and/or  creditworthiness,  and requiring
the execution and delivery of confidentiality  agreements or other documents and
agreements as a condition to such prospective purchasers' receipt of information
regarding the Collateral or participation  in any public or private  foreclosure
sale process; (2) provide to prospective  purchasers the Partnership  Agreements
and business and financial information  regarding the Partnerships  available in
the files of the Administrative  Agent at the time of commencing the foreclosure
process,  without the requirement that the Administrative  Agent obtain, or seek
to  obtain,  any  updated  business  or  financial  information  or  Partnership
Agreements, or verify, or certify to prospective purchasers, the accuracy of any
such business or financial  information or Partnership  Agreements;  (3) sell at
foreclosure  all, or a portion but not all, of the rights,  titles and interests
of  Pledgor  in a  particular  Partnership  or group of  Partnerships;  it being
further  specifically  acknowledged  by Pledgor  that  limitations  or potential
limitations  on  the  transfer  of  certain  Collateral  under  the  Partnership
Agreements or other  applicable  agreements or law may limit the  Administrative
Agent's right or ability to foreclose  upon or sell certain  rights,  titles and
interests  of  Pledgor  in the  Partnerships;  (4)  offer  for  sale,  and sell,
partnership  interests  either with, or without,  first  employing an appraiser,
investment  banker, or broker with respect to the evaluation of Collateral,  the
solicitation of purchasers for Collateral, or the manner of sale of Collateral.

         (c) The  Administrative  Agent  shall  have all  rights,  remedies  and
recourse  granted in the Loan Agreement and the other Loan Documents or existing
at common law or equity (including  specifically those granted by the Code), and
such rights and  remedies (1) shall be  cumulative  and  concurrent,  (2) may be
pursued separately,  successively or concurrently  against Pledgor and any party
obligated to pay or perform the Obligations, any of the Collateral, or any other
security  for  any  of  the   Obligations,   at  the  sole   discretion  of  the
Administrative  Agent,  and (3) may be exercised  as often as occasion  therefor
shall arise, it being agreed by Pledgor that the exercise or failure to exercise
any such  rights  or  remedies  shall in no event be  construed  as a waiver  or
release thereof or of any other right, remedy or recourse.

         (d)  Notwithstanding  a  foreclosure  upon  any  of the  Collateral  or
exercise of any other remedy by the  Administrative  Agent in connection with an
Event of Default,  Pledgor shall not be subrogated  thereby to any rights of the
Administrative Agent against the Collateral or any other security for any of the
Obligations.  Pledgor shall not be deemed to be the owner of any interest in any
of  the  Obligations  until  all  of  the  Obligations  have  been  paid  to the
Administrative Agent and are fully performed and discharged.

         (e)  All  recitals  in  any  instrument  of  assignment  or  any  other
instrument executed by the Administrative  Agent incident to the sale, transfer,
assignment or other  disposition  or  utilization  of the Collateral or any part
thereof  hereunder  shall be presumptive  evidence of the matters stated therein
and all  prerequisites  of such sale or other action  contained in such recitals
shall be presumed to have been performed or to have occurred.


<PAGE>


         SECTION  5.5  Waivers  by  Pledgor.  In case of any  Event of  Default,
neither Pledgor nor anyone claiming by, through or under Pledgor,  to the extent
Pledgor  may  lawfully  so  agree,  shall or will set up,  claim or seek to take
advantage of any appraisement,  valuation, stay, extension or redemption law now
or hereafter in force in any locality  where any of the  Collateral  is situated
for purposes of applicable law, in order to prevent or hinder the enforcement of
this  Agreement,  or the  absolute  sale of the  Collateral,  or the  final  and
absolute putting into possession  thereof,  immediately  after such sale, of the
purchaser thereof;  and Pledgor in Pledgor's own right and for all who may claim
under Pledgor, hereby waives, to the fullest extent that Pledgor may lawfully do
so, the benefit of any and all right to have the  Collateral  marshaled upon any
enforcement of the Security  Interests  herein granted,  and Pledgor agrees that
the  Administrative  Agent or any  court  having  jurisdiction  to  enforce  the
Security Interests may sell the Collateral in parts or as an entirety.

         SECTION 5.6  Application of Proceeds.  The  Administrative  Agent shall
apply  the  proceeds  of any  foreclosure  sale or  other  realization  upon the
Collateral  as follows  (as  modified,  if  necessary,  by the  requirements  of
applicable law):

         (a) First,  to the payment of all reasonable  costs and expenses of any
foreclosure   and  collection   hereunder  and  all  proceedings  in  connection
therewith, including reasonable compensation to Administrative Agent's counsel;

         (b) Then,  to the  reimbursement  of the  Administrative  Agent for all
disbursements made by the Administrative  Agent for taxes,  assessments or liens
superior to the Security Interests and which the Administrative Agent shall deem
expedient to pay;

     (c) Then, to the  reimbursement of the  Administrative  Agent for any other
disbursements  made by, or reasonable  expenses incurred by, the  Administrative
Agent in accordance with the terms hereof;

     (d) Then, to the Prime  Administrative  Agent until all secured obligations
of Pledgor to it and the Prime Lenders are paid;

     (e) Then,  to the Secured  Indebtedness,  in any manner  determined  by the
Administrative Agent in its sole discretion; and

     (f) The remainder of such proceeds, if any, shall be paid to Pledgor.

         The foregoing  application  provisions shall apply not only to proceeds
resulting from foreclosure but also to proceeds or distributions  resulting from
any other claim,  (including claims made in bankruptcy  proceedings),  action or
proceeding  to  enforce  or  protect  the  Administrative  Agent's  lien  in the
Collateral.

         SECTION  5.7  Enforcement  of  Secured  Indebtedness.  Nothing  in this
Agreement  shall affect or impair the  unconditional  and absolute  right of the
Administrative  Agent to enforce the Secured  Indebtedness  as and when the same
shall become due in accordance  with the terms of the Loan Documents  whether by
acceleration or otherwise.

                                   ARTICLE VI

                                  MISCELLANEOUS

         SECTION 6.1 Terms Commercially Reasonable.  The terms of this Agreement
shall be deemed  commercially  reasonable  within  the  meaning  of the  Uniform
Commercial Code in effect and applicable hereto.

         SECTION 6.2 Headings.  The headings of articles and sections herein are
inserted only for convenience and shall in no way define,  describe or limit the
scope or intent of any provision of this Agreement.


<PAGE>


         SECTION   6.3   Amendments.   No   change,   amendment,   modification,
cancellation  or discharge of any  provision  of this  Agreement  shall be valid
unless consented to in writing by the Administrative  Agent and Pledgor (subject
to the terms of the Loan Agreement).

         SECTION  6.4  Assignment  of the  Administrative  Agent's  Rights.  The
Administrative  Agent  shall have the right to assign all or any  portion of its
rights  under  this  Agreement  to  any  subsequent  holder  or  holders  of the
Obligations.

         SECTION  6.5 Parties in  Interest.  As and when used  herein,  the term
"Pledgor"  shall mean and include  Pledgor  herein named and his  successors and
permitted assigns,  and the term  "Administrative  Agent" shall mean and include
the  Administrative  Agent herein named and his successors and assigns,  and all
covenants and  agreements  herein shall be binding upon and inure to the benefit
of Pledgor and the Administrative  Agent and their respective assigns,  provided
that  Pledgor  shall have no right to assign his rights  hereunder  to any other
Person  except  in  connection  with  a  transfer  of the  Collateral  permitted
hereunder.

         SECTION  6.6  APPLICABLE  LAWS.  THIS  AGREEMENT  SHALL  BE  CONSTRUED,
INTERPRETED  AND  ENFORCED  UNDER AND PURSUANT TO THE LAWS OF THE STATE OF TEXAS
AND  APPLICABLE  FEDERAL LAW. IF ANY  PROVISION OF THIS  AGREEMENT IS HELD TO BE
INVALID  OR  UNENFORCEABLE,   THE  VALIDITY  AND  ENFORCEABILITY  OF  THE  OTHER
PROVISIONS OF THIS AGREEMENT SHALL REMAIN UNAFFECTED.

         SECTION 6.7 Notices.  Any notices or other  communications  required or
permitted to be given by this Agreement or any other  documents and  instruments
referred  to herein  must be given in  accordance  with  Section  11 of the Loan
Agreement, to the address of such party as follows:

         If to the Administrative Agent:       515 Congress Avenue, 11th Floor

                                               Austin, Texas 78701

                                               Attn: Wade Morgan

         If to Pledgor:                        1301 Capital of Texas Highway

                                               Suite C-300

                                               Austin, Texas 78746-6550

                                               Attn: Treasurer

         SECTION 6.8  Financing  Statement.  The  Administrative  Agent shall be
entitled  at any  time to file a  photographic  or  other  reproduction  of this
Agreement as a financing statement,  but the failure of the Administrative Agent
to do so shall not impair the validity or enforceability of this Agreement.

         SECTION  6.9  Obligations  Absolute.  All  rights and  remedies  of the
Administrative  Agent hereunder,  and all obligations of the Pledgor  hereunder,
shall be absolute and unconditional irrespective of:

               (a) any lack of validity or  enforceability of the Loan Agreement
          or any  of  the  other  Loan  Documents  or  any  other  agreement  or
          instrument relating to any of the foregoing;

                  (b) any change in the time, manner, or place of payment of, or
         in any  other  term of,  all or any of the  Obligations,  or any  other
         amendment  or waiver of or any consent to any  departure  from the Loan
         Agreement or any of the other Loan Documents;


<PAGE>


               (c) any exchange, release, or nonperfection of any Collateral, or
          any release or amendment or waiver of or consent to any departure from
          any guarantee, for all or any of the Obligations; or

                  (d) any other circumstance  (other than payment in full of the
         Obligations) that might otherwise constitute a defense available to, or
         a discharge of, Pledgor.

         SECTION 6.10  Counterparts.  This Agreement may be executed in multiple
counterparts,  each of which shall be deemed to be an original, but all of which
shall  constitute  one and the  same  instrument,  and in  making  proof of this
Agreement it shall not be necessary to produce or account for more than one such
counterpart.

         SECTION  6.11 ENTIRE  AGREEMENT.  THIS  AGREEMENT  EMBODIES  THE FINAL,
ENTIRE  AGREEMENT  OF  PLEDGOR,  THE  AGENTS  AND THE  LENDERS  WITH  RESPECT TO
PLEDGOR'S PLEDGE OF THE PLEDGED  PARTNERSHIP  INTERESTS AND RESTATES ANY AND ALL
PRIOR COMMITMENTS,  AGREEMENTS,  REPRESENTATIONS,  AND  UNDERSTANDINGS,  WHETHER
WRITTEN OR ORAL,  RELATING TO THE  SUBJECT  MATTER  HEREOF.  THIS  AGREEMENT  IS
INTENDED  BY  PLEDGOR,  THE  AGENTS  AND THE  LENDERS  AS A FINAL  AND  COMPLETE
EXPRESSION  OF THE TERMS OF THIS  AGREEMENT,  AND NO COURSE OF  DEALING  BETWEEN
PLEDGOR,  THE  AGENTS  OR THE  LENDERS,  NO  COURSE  OF  PERFORMANCE,  NO  TRADE
PRACTICES,  AND  NO  EVIDENCE  OF  PRIOR,  CONTEMPORANEOUS  OR  SUBSEQUENT  ORAL
AGREEMENTS OR  DISCUSSIONS  OR OTHER  EXTRINSIC  EVIDENCE OF ANY NATURE SHALL BE
USED TO CONTRADICT, VARY, SUPPLEMENT OR MODIFY ANY TERM OF THIS AGREEMENT. THERE
ARE NO ORAL AGREEMENTS AMONG PLEDGOR, THE AGENTS AND THE LENDERS.

                     [REMAINDER OF PAGE INTENTIONALLY BLANK.

                            SIGNATURE PAGES FOLLOW.]


<PAGE>



                          Pledge and Security Agreement

         IN WITNESS  WHEREOF,  Pledgor has executed this Agreement as of the day
and year first above written.

                                    PLEDGOR:

                                                     OHIO LITHO, INC.,
                                                       a Delaware corporation

                                                     By: /s/ Teena E. Belcik
                                                              Teena E. Belcik
                                                              Treasurer


<PAGE>



                                                                       Exhibit A



                                    EXHIBIT A

                                  PARTNERSHIPS

Ohio Mobile Lithotripter, Ltd.

Ohio Mobile Lithotripter II, Ltd.




<PAGE>



                                                                       Exhibit B



                                    EXHIBIT B

                             PARTNERSHIP AGREEMENTS

First  Amended and  Restated  Agreement  of Limited  Partnership  of Ohio Mobile
Lithotripter,  Ltd. dated August 1, 1991, as amended by First Amendment to First
Amended and Restated  Agreement of Limited  Partnership dated as of December 31,
1992

Certificate of Limited Partnership of Ohio Mobile  Lithotripter,  Ltd. dated May
21, 1991

First  Amended and  Restated  Agreement  of Limited  Partnership  of Ohio Mobile
Lithotripter II, Ltd.

Certificate of Limited  Partnership of Ohio Mobile  Lithotripter  II, Ltd. dated
August 23, 1995