MEMBERSHIP INTEREST

                         TRANSFER RESTRICTION AGREEMENT

     This Membership Interest Transfer Restriction  Agreement (this "Agreement")
is entered  into  effective as of the 1st day of March,  2000,  by and among MBC
Holding  Company,  L.L.C.,  a Texas limited  liability  company (the "Company"),
Prime RVC,  Inc., a Delaware  corporation  ("Prime"),  Paul Michael  Mann,  M.D.
("Mann"),  Ralph  G.  Berkeley,  M.D.  ("Berkeley"),  Michael  B.  Caplan,  M.D.
("Caplan"),  and Mark F. Micheletti  ("Micheletti").  Mann, Berkeley, Caplan and
Micheletti,  together with any  subsequent  Members in the Company who hereafter
execute this Agreement, are collectively referred to herein as the "Members".

                                R E C I T A L S:

             WHEREAS,  Mann, Berkeley,  Caplan and Micheletti own all the issued
and  outstanding  membership  interests  of the  Company  (all  such  membership
interests,  together with any hereafter acquired, are hereinafter referred to as
the "Membership Interests"); and

             WHEREAS, this Agreement is a "Transaction  Document," as defined in
that  certain  Contribution  Agreement  (the  "Contribution   Agreement")  dated
effective March 1, 2000, by and among Prime,  Prime MBC, L.L.C., a Texas limited
liability  company,  the  Company,  Mann  Berkeley  Eye  Center,  P.A.,  a Texas
professional association, Mann, Berkeley, Caplan and Micheletti.

             WHEREAS,  the  Members,  the Company and Prime desire to enter into
this Agreement to control the distribution of ownership interests in the Company
and to promote the harmonious management of the Company's affairs.

             NOW,  THEREFORE,  in  consideration  of the  foregoing,  the mutual
covenants and agreements contained herein, and for other valuable consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

                                    ARTICLE I

               PERMITTED TRANSFERS; RESTRICTIONS AGAINST TRANSFER

As used in this Agreement,  "Permitted Transfers" shall mean any transfer of all
or any  part of any  Member's  Membership  Interest  to (i) the  members  of the
immediate  family of the Member or a trust or trusts for the  benefit of members
of the immediate family of the Member, provided that after any such transfer the
Member  retains  the sole  express  right to vote,  or direct  the votes of, the
Membership  Interest,  (ii) any other  Member,  provided that after any transfer
pursuant to this subsection (ii) is consummated,  Mann,  Berkeley and Caplan (or
trusts  that  hold  Membership  Interests  as a result  of  Permitted  Transfers
subsection (i) above) must  collectively own in the aggregate at least fifty-one
percent (51%) of the total outstanding  Membership  Interests of the Company, or
(iii) Prime. Any Member transferring all or a portion of its Membership Interest
pursuant to a Permitted  Transfer  shall give  written  notice of the  Permitted
Transfer  (containing the same  information as required for notice under Section
2.1.1) to Prime and the other  Members  fifteen (15) days prior to the effective
date of the Permitted Transfer. Except for a Permitted Transfer, or as otherwise
provided  in this  Agreement,  a Member  shall  not  transfer,  assign,  pledge,
hypothecate,  or in any way alienate any  Membership  Interest,  or any interest
therein,  whether  voluntarily  or by operation of law, or by gift or otherwise,
without the prior written  consent of the Company,  the other Members and Prime,
which  consent  may be  withheld  in their  sole and  absolute  discretion.  Any
purported transfer in violation of any provision of this Agreement shall be void
and  ineffectual,  shall not  operate to transfer  any  interest or title to the
purported  transferee,  and shall give the Company,  the other Members and Prime
options to purchase such Membership Interest in the manner and on the conditions
hereinafter provided. As used in this Agreement, "Option Members" shall mean all
Members of the Company except the Member who, prior to the proposed  transfer or
the  incident  resulting  in the  proposed  transfer  of all or a  portion  of a
Membership Interest, owned such interest.

                                   ARTICLE II

                                     OPTIONS

2.1      OPTION UPON VOLUNTARY TRANSFER.

             2.1.1Notice  of  Intention  to  Transfer.  If a Member  intends  to
voluntarily  transfer any of its Membership  Interest,  other than pursuant to a
Permitted  Transfer,  to any person other than the Company,  and does not obtain
the written consents required in ARTICLE I hereof, the Member shall give written
notice to the other  Members and Prime  stating (i) the  intention to transfer a
Membership  Interest,  (ii) the amount of Membership Interest to be transferred,
(iii) the name, business and residence address of the proposed transferee,  (iv)
the  nature  and  amount of the  consideration,  and (v) the other  terms of the
proposed sale.

             2.1.2Option  to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days after  receipt of the notice of intent to transfer,  an
option  to  purchase  all  or  any  portion  of  the  Membership   Interest  the
transferring Member intends to transfer,  for the price and upon the other terms
stated in the notice of intent to transfer.  If the Option Members fail,  within
such 30-day period,  to exercise  their purchase  option (by delivery of written
notice) with respect to the entire Membership  Interest being  transferred,  the
Option  Members shall be deemed to have elected not to exercise  their  purchase
option with respect to such unpurchased Membership Interest.  Upon any notice of
non-exercise (or deemed  non-exercise) by the Option Members,  Prime shall have,
and may exercise  within 30 days of receipt of notice of such  non-exercise  (or
deemed  non-exercise),  an option to purchase all of such  remaining  Membership
Interest upon the same terms and conditions.

             2.1.3Death  Before Closing.  If a Member who proposed to transfer a
Membership  Interest  dies  prior  to the  closing  of  the  sale  and  purchase
contemplated  by this  Section  2.1, the  Membership  Interest of such  deceased
Member shall be the subject of sale and purchase under Section 2.3.

             2.1.4Allowable  Consideration.  All parties hereto  acknowledge and
agree that it would be  impractical  to exercise  an option to purchase  arising
pursuant to this Section 2.1 whenever the proposed  consideration to be received
by the transferring  Member is other than cash or cash  equivalents.  Therefore,
the parties agree that no transfer  shall be permitted and no option shall arise
pursuant to this Section 2.1 whenever the  consideration to be received from the
proposed transferee is other than cash or cash equivalents.

2.2      OPTION UPON CERTAIN INVOLUNTARY TRANSFERS.

             2  2.1Exercise  Event and  Notice.  The  filing of a  voluntary  or
involuntary petition of bankruptcy by or on behalf of a Member, an assignment by
a Member of any of its Membership Interest, or of any right or interest therein,
for the benefit of creditors, or the voluntary transfer,  transfer by law or any
other transfer,  of any Membership Interest, or of any right or interest therein
(other  than  transfers  governed by ARTICLE I or  Sections  2.1,  2.3 or 2.4 or
ARTICLE  VII  hereof),  shall  give the other  Members  and Prime the  option to
purchase the  Membership  Interest of such bankrupt  Member or such  transferred
Membership  Interest  as  provided  herein.  Upon the filing of a  voluntary  or
involuntary  petition of bankruptcy by or on behalf of a Member or an assignment
by  Member  of any of its  Membership  Interest,  or of any  right  or  interest
therein, for the benefit of creditors, the Member or its personal representative
shall promptly give written  notice of such  occurrence to the other Members and
Prime. In the event of a transfer of Membership  Interest,  as described  above,
the Member  transferring  such  Membership  Interest shall promptly give written
notice of such transfer to the other Members and Prime.

             2.2.2Option  to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days after receipt of the notice of the applicable  exercise
event,  an option to purchase all or any portion of the Membership  Interest the
bankrupt or transferring Member intends to transfer,  for the price and upon the
other terms hereinafter provided. If the Option Members fail, within such 30-day
period,  to exercise their purchase  option (by delivery of written notice) with
respect to the entire Membership Interest being transferred,  the Option Members
shall be deemed to have  elected  not to  exercise  their  purchase  option with
respect to such unpurchased Membership Interest. Upon any notice of non-exercise
(or deemed  non-exercise)  by the Option  Members,  Prime  shall  have,  and may
exercise  within 30 days of  receipt of notice of such  non-exercise  (or deemed
non-exercise),  an option to purchase all of such remaining  Membership Interest
for the price and upon the other terms hereinafter provided.

2.3      PURCHASE AND SALE OF MEMBERSHIP INTEREST UPON DEATH.

             2.3.1Notice   of  Death.   Upon  the  death  of  the  Member,   the
representative  of the estate of the deceased Member shall promptly give written
notice of the death to the other Members and Prime.

             2.3.2Option  to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days  after  receipt  of the  notice of death,  an option to
purchase all or any portion of the Membership  Interest of the deceased  Member,
for the price and upon the  other  terms  hereinafter  provided.  If the  Option
Members fail,  within such 30-day period,  to exercise their purchase option (by
delivery of written  notice)  with  respect to the  entirety of such  Membership
Interest,  the Option  Members  shall be deemed to have  elected not to exercise
their purchase option with respect to such unpurchased Membership Interest. Upon
any notice of non-exercise (or deemed non-exercise) by the Option Members, Prime
shall  have,  and may  exercise  within  30 days of  receipt  of  notice of such
non-exercise  (or  deemed  non-exercise),  an  option  to  purchase  all of such
remaining Membership Interest for the price and upon the other terms hereinafter
provided.

2.4  OPTION UPON DEATH OF A MEMBER'S SPOUSE, TERMINATION OF MARITAL RELATIONSHIP
     OR PARTITION OF COMMUNITY PROPERTY.

             2.4.1Death of Member's Spouse. Each Member and each Member's spouse
agree that in the event the spouse of a Member  predeceases such Member and such
Member does not succeed by the spouse's  last will and testament or by operation
of law to any interest  (including,  without  limitation,  a community  property
interest) of the spouse in the Membership Interest,  such Member shall have, and
may exercise within 60 days after the death of the spouse, an option to purchase
all or any  portion of the  spouse's  interest  for the price and upon the other
terms hereinafter  provided.  If the Member fails, within such 60-day period, to
exercise his purchase option (by delivery of written notice) with respect to the
entirety of such spouse's interest,  that Member shall be deemed to have elected
not to exercise his purchase option with respect to such spouse's interest. Upon
any notice of non-exercise (or deemed  non-exercise)  by the Member,  the Option
Members shall then have,  and may exercise  within 30 days after receipt of such
non-exercise (or deemed non-exercise),  an option to purchase all or any portion
of the  deceased  spouse's  interest,  for the price  and upon the  other  terms
hereinafter  provided. If the Option Members fail, within such 30-day period, to
exercise their purchase  option (by delivery of written  notice) with respect to
the entirety of such deceased  spouse's  interest,  the Option  Members shall be
deemed to have  elected not to exercise  their  purchase  option with respect to
such unpurchased deceased spouse's interest. Upon any notice of non-exercise (or
deemed  non-exercise) by the Option Members,  Prime shall have, and may exercise
within  30  days  of  receipt  of  notice  of  such   non-exercise   (or  deemed
non-exercise),  an option  to  purchase  all of such  remaining  portion  of the
deceased  spouse's  interest for the price and upon the other terms  hereinafter
provided.

             2.4.2Termination of Marital  Relationship or Partition of Community
Property. In the event a divorce,  annulment or other proceeding for termination
of the  marital  relationship  is  filed by or  against  a  Member,  or upon the
initiation  of any voluntary or  involuntary  attempt to partition the community
property  estate between a Member and such Member's  spouse for any reason,  the
Member shall  promptly give written  notice to the other  Members and Prime,  of
such event.  The Member shall have, and may exercise within 60 days of giving of
such notice, an option to purchase all or any portion of the departing  spouse's
interest in such Membership Interest (including without limitation any community
property  interest,  for purposes of this  Section),  for the price and upon the
other  terms  hereinafter  provided.  If the Member  fails,  within  such 60-day
period,  to exercise  his purchase  option (by delivery of written  notice) with
respect to the entirety of such spouse's  interest,  that Member shall be deemed
to have  elected  not to  exercise  his  purchase  option  with  respect to such
spouse's interest.  Upon any notice of non-exercise (or deemed  non-exercise) by
the Member,  the Option Members shall then have, and may exercise within 30 days
after  receipt  of such  non-exercise  (or  deemed  non-exercise),  an option to
purchase all or any portion of the departing  spouse's  interest,  for the price
and upon the other  terms  hereinafter  provided.  If the Option  Members  fail,
within such 30-day period,  to exercise  their  purchase  option (by delivery of
written  notice)  with  respect  to the  entirety  of  such  departing  spouse's
interest,  the Option  Members  shall be deemed to have  elected not to exercise
their  purchase  option  with  respect to such  unpurchased  departing  spouse's
interest. Upon any notice of non-exercise (or deemed non-exercise) by the Option
Members,  Prime shall have, and may exercise within 30 days of receipt of notice
of such non-exercise (or deemed non-exercise), an option to purchase all of such
remaining portion of the departing  spouse's interest for the price and upon the
other terms hereinafter provided.

2.5      ALTERNATE NOTICES.

             The failure of any  person,  whether a party to this  Agreement  or
otherwise,  to give notice of the occurrence of an Exercise Event (as defined in
Section 4.3) as contemplated herein shall not operate to prevent the creation of
any option which would otherwise arise pursuant to this ARTICLE II. Any party to
this  Agreement who has actual  knowledge of the occurrence of an Exercise Event
may give the required written notice of the occurrence of an Exercise Event, and
upon the giving of such written  notice the options  shall be created and become
exercisable  to the  same  extent  as if such  notice  was  given  by the  party
initially contemplated above. For instance, and purely by way of example, in the
event of the death of a Member,  another  Member having actual  knowledge of the
Member's  death  may give the  notice  initially  contemplated  to be given by a
representative  of the estate of the deceased  Member  pursuant to Section 2.3.1
above,  whereupon the Option  Members'  option  described in Section 2.3.2 would
arise and become  exercisable to the same extent as if the notice had been given
by the representative of the estate of the deceased Member.

2.6      OPPORTUNITY TO CURE.

         Before Prime may exercise any option to purchase a Membership  Interest
pursuant to Sections 2.2, 2.3 or 2.4, Prime shall deliver  written notice of its
intent to exercise its right ("Cure  Notice") to the Option  Members,  who shall
have ten days from the date of receipt  of such Cure  Notice to  exercise  their
rights and purchase such Membership  Interest,  upon such terms as are otherwise
provided  herein.  If each of the Option  Members do not  exercise  their rights
within ten days after  receipt of the Cure  Notice,  then Prime may exercise its
options under this Article II.

                                   ARTICLE III

                   EXERCISE OF OPTIONS; EFFECT OF NON-EXERCISE

3.1      MANNER OF EXERCISE OF OPTIONS.

             All options granted in, or arising pursuant to, ARTICLE II shall be
exercised by a written notice to that effect  delivered within the time provided
for the exercise of the option.

3.2      COMPLETE EXERCISE OF OPTIONS.

             Notwithstanding  anything  herein to the  contrary,  the holders of
options granted in, or arising pursuant to, ARTICLE II must,  either alone or in
the  aggregate,  exercise the options in such a manner as to purchase all of the
Membership  Interest (or interest therein) subject to such options,  and failure
to do so shall cause a forfeiture of the options.

3.3      MULTIPLE OPTION HOLDERS.

             In cases  where an option is held by more than one  Option  Member,
each  purchasing  Option  Member  shall  be  entitled  to  purchase  his  or her
proportionate  share of the Membership Interest subject to the option. An Option
Member's  proportionate  share  shall  equal  the  total  amount  of  Membership
Interests  subject to the option multiplied by a fraction the numerator of which
is the  amount  of  Membership  Interests  held by such  Option  Member  and the
denominator  of which shall be the amount of  Membership  Interests  held by all
Option Members electing to exercise the option.

3.4      EFFECT OF NON-EXERCISE OF OPTIONS.

             If the  holders of options  granted  or  arising  pursuant  to this
Agreement do not exercise  their  options,  or such  options are  forfeited,  as
provided herein,  the person or persons  acquiring the Membership  Interests (or
interest  therein)  that  were  the  subject  of the  options  shall  execute  a
counterpart  of this  Agreement  and  become a party  hereto and shall hold such
Membership  Interests  subject to all the terms and conditions  provided herein,
and any transfer of such Membership  Interests (or interest  therein) shall only
be made in accordance  with the terms and  conditions  provided  herein.  In the
event the person or persons  acquiring  the  Membership  Interests  (or interest
therein)  fail to execute a  counterpart  of this  Agreement  and become a party
hereto,  such transfer shall be void and  ineffectual,  and shall not operate to
transfer any interest or title to the purported  transferee and such  Membership
Interests shall thereafter be subject to cancellation and  extinguishment by the
Company,  without  consideration  therefor.  In  addition,  in  the  event  of a
voluntary  transfer  subject to the provisions of Section 2.1, upon the lapse or
forfeiture of the options arising pursuant to that Section, the Member proposing
the  transfer  shall have the right to  effectuate  the  transfer of  Membership
Interests  in  accordance  with the  terms  stated  in the  notice  of intent to
transfer,  and the  transferee of such  Membership  Interests  shall execute and
become a party to this  Agreement  and  shall  hold  such  Membership  Interests
subject to all of its terms and conditions.  Provided further, however, any such
transfer of Membership  Interests shall be void and  ineffectual,  and shall not
operate to transfer any interest or title to the  purported  transferee,  if (i)
the  transfer  is not upon the terms or is not to the  transferee  stated in the
notice of intent to transfer,  or (ii) the transfer is not closed within 10 days
of receipt of written notice of the election not to exercise,  or the forfeiture
of, all applicable options.

                                   ARTICLE IV

                                 PURCHASE PRICE

4.1      PURCHASE PRICE.

             The  purchase  price of the  Membership  Interests  to be purchased
pursuant to options granted, held or exercised pursuant to Sections 2.2, 2.3 and
2.4  hereof,  shall be the amount  calculated  in  accordance  with  Section 4.2
hereof.

4.2      CALCULATION OF PURCHASE PRICE.

             When  determined in accordance  with this Section 4.2, the purchase
price for the Membership  Interest or any portion  thereof or spouse's  interest
therein shall be equal to the Appraised  Value of the Membership  Interest as of
the Valuation Date (as defined in Section 4.3 hereof), reduced when necessary to
reflect the purchase of less than a one hundred  percent (100%) interest in each
of the Membership Interests to be transferred (for example:  reduced by one-half
when a  spouse's  interest  is only an  undivided  one-half  community  property
interest in each of the Membership  Interests of a Member spouse).  For purposes
of this Agreement,  the "Appraised Value" of a Membership  Interest shall be (i)
based on the overall value of the Company as a going concern, expressed in a per
Membership Interest unit amount without  consideration to whether the Membership
Interest,  or interest therein,  being transferred  constitutes a controlling or
minority  interest in the Company,  and (ii) determined by a certified  business
appraiser,  selected  by the  Company,  that is a member of either the  American
Society of Appraisers or the Institute of Business  Appraisers;  but if a Member
or Prime  disagrees  with such  determination  that  Member or Prime may, at its
expense,  have another certified  business  appraiser that is a member of one or
both of the above named professional  organizations  determine the value, and if
the two appraisers cannot agree upon a value, they shall mutually select a third
certified  business  appraiser  (that  meets  the  above  described   membership
requirements) who shall,  together with the first two appraisers,  determine the
value of the  Membership  Interest by majority  vote.  The expense of such third
appraiser  shall  also be paid by the  Member or Prime,  as the case may be, who
disagrees  with the value  determination  of the Company's  original  appraiser,
unless the appraised value ultimately  determined is more than ten percent (10%)
greater than the value determined by the Company's original appraiser.

4.3      CERTAIN DEFINITIONS.

             As used herein,  the term "Valuation  Date" shall mean and refer to
the end of the fiscal year of the Company  immediately  preceding  the  Exercise
Event,  unless the purchasing party elects to use the alternate  valuation date,
in which  event the  Valuation  Date  shall be the end of the month  immediately
preceding the Exercise  Event. As used herein,  the term "Exercise  Event" shall
mean and refer to the event or  circumstance  described  in  ARTICLE  II of this
Agreement, as a result of which the Company, a Member, or Prime, as the case may
be in the first  instance,  becomes  entitled  to  exercise  a  purchase  option
hereunder.

                                    ARTICLE V

                          PAYMENT OF THE PURCHASE PRICE

5.1      PAYMENT.

             Except as otherwise  provided in this Agreement,  including Section
2.1, the purchase price for a Membership Interest to be purchased from a selling
party shall either: (i) be paid in cash; or (ii) at the option of the purchasing
party,  up to seventy  percent (70%) of the purchase  price may be deferred with
the remainder paid in cash at the closing.

5.2      PROMISSORY NOTE.

             If the purchasing  party elects to defer part of the purchase price
by the execution and delivery of a promissory  note, the deferred portion of the
price shall be evidenced by the promissory  note of the purchasing  party to the
order of the selling party payable in sixty (60) equal monthly  installments  of
principal  and interest on or before the first day of each month  beginning  the
month next following the date of closing. The interest rate for such installment
promissory  note shall be equal to the prime or base rate on corporate  loans at
large U.S.  money center  commercial  banks as  published  in the "Money  Rates"
column of the Wall  Street  Journal  on the date of  exercise  of the  option to
purchase  (or, if such option is not  exercised  on a date on which such rate is
published, the next following date on which such rate is published). In no event
shall the interest rate exceed the maximum legal  interest rate then  prevailing
for such obligations in the state of Texas. The note shall be secured by a first
lien security interest in the Membership Interest transferred and the purchasing
party shall  deliver  certificates  evidencing  the  Membership  Interest to the
selling party and take such further action as is reasonably necessary to perfect
the security interest.

                                   ARTICLE VI

                                   THE CLOSING

             Unless otherwise agreed by the parties, the closing of the sale and
purchase of a Membership  Interest shall take place at the principal  offices of
the Company within sixty (60) days after the exercise of any option  provided by
this Agreement.  Each party hereto  (including the spouses of the Members) shall
bear its own transaction  costs,  including  legal and accounting  fees, if any,
attributable to any transfer of a Membership Interest,  or any interest therein,
pursuant to this  Agreement.  Upon the closing,  the selling party shall deliver
its  Membership  Interest  to the  purchaser  free and  clear of all  liens  and
encumbrances,  and shall deliver to the Company its  resignation and that of all
of its nominees, if any, as officers and directors of the Company and any of the
Company's subsidiaries.  The selling party shall deliver to the purchasing party
at closing, all appropriate documents of transfer,  including without limitation
bills of sale, assignments or other instruments of conveyance. As a condition to
any closing of the sale and purchase of a  Membership  Interest (or any interest
therein) pursuant to this Agreement:  (i) the selling party shall be indemnified
by the purchasing party (in a form reasonably satisfactory to the selling party)
for all the Company's liabilities,  whether fixed or contingent,  to lenders and
others,  incurred prior to the closing of the  transaction,  (ii) the purchasing
party and/or the Company  shall cause the release of any personal  guaranties by
the  selling  party that the  selling  party may have  granted to the  Company's
lenders or other  creditors  or which may have  otherwise  been  provided by the
selling party for the benefit of the Company,  and (iii) if the selling party is
a creditor of the Company, the purchasing party shall unconditionally  guarantee
the debt of the Company to the  selling  party and execute  such  documents  and
instruments   of  guarantee  as  may  be  necessary  in  connection   therewith.
Furthermore,  and as a condition to closing, in the event the selling party owes
any amounts to the Company at the time of closing,  such  indebtedness  shall be
paid in full by the selling party at or prior to the closing, or may be deducted
from and offset  against the  purchase  price by the  purchasing  party,  in the
purchasing  party's  sole  discretion.  In the event of a failure  to close as a
result of the  non-satisfaction  of the  conditions to closing set forth herein,
this  Agreement  shall  remain  in full  force  and  effect  and all  Membership
Interests  shall remain  subject to the  restrictions  contained  herein and, in
addition,  the parties hereto shall be entitled to such other remedies as may be
available in the event the failure to close constitutes a breach hereof.

                                   ARTICLE VII

                             LEGEND ON CERTIFICATES

             All Membership  Interests now or hereafter owned by the Members, or
their  permitted  transferees,  shall  be  subject  to the  provisions  of  this
Agreement,  and any  certificates  representing  same shall  bear the  following
legend:

             "THE  MEMBERSHIP   INTEREST   REPRESENTED   HEREBY  AND  THE  SALE,
             ASSIGNMENT,  TRANSFER,  PLEDGE  OR OTHER  DISPOSITION  THEREOF  ARE
             SUBJECT TO CERTAIN RESTRICTIONS  CONTAINED IN A MEMBERSHIP INTEREST
             TRANSFER  RESTRICTION  AGREEMENT  AMONG THE  COMPANY AND THE WITHIN
             NAMED MEMBER, AND ANY AMENDMENT  THERETO.  THE AGREEMENT LIMITS THE
             USE OF THIS MEMBERSHIP  INTEREST AS COLLATERAL FOR ANY LOAN WHETHER
             BY PLEDGE,  HYPOTHECATION  OR OTHERWISE.  A COPY OF THE  MEMBERSHIP
             INTERES   TRANSFER   RESTRICTION   AGREEMENT  AND  ALL   APPLICABLE
             AMENDMENTS  THERETO  WILL BE FURNISHED BY THE COMPANY TO THE HOLDER
             HEREOF  WITHOUT  CHARGE UPON WRITTEN  REQUEST TO THE COMPANY AT ITS
             PRINCIPAL PLACE OF BUSINESS OR REGISTERED OFFICE."

                                  ARTICLE VIII

                            TERMINATION OF AGREEMENT

             This Agreement and all restrictions on Membership Interest transfer
created hereby shall terminate on the occurrence of any of the following events:

             (a)  The bankruptcy or dissolution of the Company.

             (b) The ownership by one person of all of the Membership  Interests
of the Company which are then subject to this Agreement.

             (c) The execution of a written  instrument  by the Company,  all of
the Members who then own Membership  Interests  subject to this  Agreement,  and
Prime which terminates the same.

             (d) The date  twenty-one  (21)  years  after  the death of the last
survivor of all individuals who are parties to this Agreement.

                                   ARTICLE IX

                               GENERAL PROVISIONS

9.1      REMEDIES FOR BREACH.

             The  Membership  Interests are unique  chattels,  and each party to
this Agreement shall have the remedies which are available to him, her or it for
the violation of any of the terms of this Agreement,  including, but not limited
to, the equitable remedy of specific performance.

9.2      BINDING EFFECT.

             This  Agreement  is binding  upon and inures to the  benefit of the
Company,  its  successors  and  permitted  assigns,  to the  Members  and  their
respective heirs,  personal  representatives,  successors and permitted assigns,
and to Prime,  its successors and permitted  assigns.  This Agreement may not be
assigned,  in whole or in part, by any party hereto without the express  written
consent of all parties hereto.

9.3      PRIOR AGREEMENTS.

             This  Agreement  supersedes  all prior written and oral  agreements
between the parties regarding the subject matter hereof.

9.4      GOVERNING LAWS.

             This Agreement is executed under,  and in conformity with, the laws
of the State of Texas and shall be governed  thereby.  If any  provision of this
Agreement  shall be determined to be invalid or  unenforceable  or prohibited by
the laws of the State of Texas, this Agreement shall be considered  divisible as
to such provisions and such  provisions  shall be inoperative and shall not be a
part of the consideration  moving from any party to another party. The remaining
provisions  shall be valid and binding upon the parties and be of like effect as
though such invalid,  unenforceable  or prohibited  provisions were not included
herein.

9.5      AMENDMENT.

             This  Agreement  may be  amended  in whole  or in part  only by the
written consent of all the parties.  Such amendment shall be effective as of the
date then  determined by the parties and shall  supersede any provisions  herein
contained which are in conflict.

9.6      CAPTIONS AND GENDER.

             The captions and titles herein are for convenience only and are not
intended to include or  conclusively  define the subject matter of the text. All
pronouns and  references  thereto shall refer to the  masculine,  feminine,  and
neuter  genders,  singular  or plural,  as the  identification  of the  persons,
entities, and companies may require. The term "person" as used in this Agreement
shall include natural persons, companies,  partnerships, trusts, estates and any
other form of entity.

9.7      NOTICES.

             All notices  required to be given  hereunder  shall be deemed to be
duly given by  personally  delivering  such notice or by mailing it by certified
mail, to the Company,  to the Members,  and to Prime at the following  addresses
(which  may be  changed  by giving  written  notice of such  change to all other
parties hereto):

             To the Company:                        MBC Holding Company, L.L.C.
                                                    1200 Binz, Suite 1000
                                                    Houston, Texas 77004

             To Mann:                               Paul Michael Mann, M.D.
                                                    1200 Binz, Suite 1000
                                                    Houston, Texas 77004

             To Berkeley:                           Ralph G. Berkeley, M.D.
                                                    1200 Binz, Suite 1000
                                                    Houston, Texas 77004

             To Caplan:                             Michael B. Caplan, M.D.
                                                    1200 Binz, Suite 1000
                                                    Houston, Texas 77004

             To Micheletti:                         Mark F. Micheletti
                                                    1200 Binz, Suite 1000
                                                    Houston, Texas 77004

             To Prime:                              Prime RVC, Inc.
                                                    Attention: President
                                                    1301 Capital of
                                                        Texas Highway
                                                    Austin, Texas 78746

9.8  BINDING EFFECT OF THIS AGREEMENT ON ADDITIONAL MEMBERSHIP INTEREST ACQUIRED
     BY A MEMBER.

             In the event a Member acquires,  contracts to acquire,  or receives
any Membership  Interests of the Company which are not subject to this Agreement
at the time of acquisition,  such additional  Membership Interests of the Member
shall  be   automatically   subject  to  this  Agreement  and  any  certificates
representing  such Membership  Interests shall bear the legend prescribed herein
and this Agreement shall be amended, if necessary, to reflect the acquisition of
such Membership Interests by the Member.

9.9      EXECUTION OF DOCUMENTS.

             Whenever Membership Interests are to be purchased by the Company, a
Member, or Prime pursuant to this Agreement,  the transferor shall do all things
and execute and deliver all documents and make all transfers as may be necessary
to consummate such purchase.  In the event that the transferor  refuses to abide
by the terms and  conditions  specified  herein,  the  purchaser(s)  may  tender
payment  for such  Membership  Interest by mailing  payment to the  transferor's
attention  at the  address  of the  Company's  registered  office on file at the
office of the Texas Secretary of State.  After payment is tendered  accordingly,
the Company shall be entitled to cancel such  Membership  Interest on its books,
and reissue such Membership Interest to the purchaser(s) or, if the purchaser is
the Company,  the Company may hold such Membership Interest as treasury stock or
cancel such Membership Interest.

9.10     ACTIONS BY THE COMPANY.

             Any decision by the Company to exercise any purchase  option,  give
any notice or otherwise enforce any provisions of this Agreement,  shall be made
by a majority  vote of Members who are not then in breach of this  Agreement and
whose Membership Interests are not then the subject of any option or requirement
of notice of an Exercise Event.

                            [Signature pages follow]


<PAGE>


                                       S-2

                                SIGNATURE PAGE TO

                               MEMBERSHIP INTEREST

                         TRANSFER RESTRICTION AGREEMENT

             EXECUTED as of the date first mentioned above.

             COMPANY:                       MBC Holding Company, L.L.C.


                                                By:
                                                Printed Name:__________________
                                                Title:

         MANN:

                                                     Paul Michael Mann, M.D.


         BERKELEY:

                                                     Ralph G. Berkeley, M.D.


         CAPLAN:

                                                     Michael B. Caplan, M.D.


         MICHELETTI:

                                                     Mark F. Micheletti

         PRIME:                             Prime RVC, Inc.

                                                  By:
                                                  Printed Name:
                                                  Title:


<PAGE>


                                SPOUSAL CONSENTS

             The  undersigned   spouse  of  Paul  Michael  Mann,  M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the membership  interest of MBC Holding Company,  L.L.C.,  referred to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                            Signature:
                                            Printed Name:

             The  undersigned  spouse  of  Ralph  G.  Berkeley,   M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the membership  interest of MBC Holding Company,  L.L.C.,  referred to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                            Signature:
                                            Printed Name:

             The  undersigned  spouse  of  Michael  B.  Caplan,   M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the membership  interest of MBC Holding Company,  L.L.C.,  referred to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                            Signature:
                                            Printed Name:

             The undersigned  spouse of Mark F. Micheletti  hereunto  subscribes
her name in evidence of her agreement and consent to the disposition made of any
interest  she may have,  including  any  community  property  interests,  in the
membership interest of MBC Holding Company, L.L.C., referred to in the foregoing
Agreement, and to all other provisions of such Agreement.

                                            Signature:
                                            Printed Name: