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                            STOCK PURCHASE AGREEMENT
                                        
                                        
                                    between
                                        
                                        
                            COBE LABORATORIES, INC.
                                        
                                        
                                      and
                                        
                                        
                              REN CORPORATION-USA
                                        
                                        
                                        
                                        
                          Dated as of February 9, 1992
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
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                          TABLE OF CONTENTS
                           ----------------

Section                                               Page
-------                                               ----

                            ARTICLE I
                           DEFINITIONS

1.01      Definitions .................................  1

                                   
                              ARTICLE II
                     PURCHASE AND SALE OF SHARES;
                               CLOSING

2.01      Authorization, Purchase and
            Sale of Shares ...........................   4
2.02      Closing ....................................   4

                                   
                             ARTICLE III
            REPRESENTATIONS AND WARRANTIES OF THE COMPANY
                                   

3.01      Organization and Qualification;
            Subsidiaries ..............................  5
3.02      Charter of Incorporation and By-Laws ........  5
3.03      Capitalization ..............................  6
3.04      Authority Relative to This Agreement ........  6
3.05      No Conflict; Required Filings and
            Consents ..................................  7
3.06      Common Stock ................................  8
3.07      SEC Filings; Financial Statements ...........  8
3.08      Private Offering ............................  9
3.09      Brokers ..................................... 10

                                   
                              ARTICLE IV
                  REPRESENTATIONS AND WARRANTIES OF
                            THE PURCHASER
                                   

4.01      Corporate Organization ...................... 10
4.02      Authority Relative to This Agreement ........ 10
4.03      No Conflict; Required Filings and Consents... 11
4.04      Funds ....................................... 11
4.05      Securities Act .............................. 11
4.06      Brokers ..................................... 12



                                   
                                 (ii)

Section                                               Page
-------                                               ----

                                  
                              ARTICLE V
                        ADDITIONAL AGREEMENTS


5.01      Conduct of Business by the Company
            Pending the Closing ....................... 13
5.02      Regulatory and Other Authorizations ......... 13
5.03      Access to Information ....................... 13
5.04      Notification of Certain Matters ............. 14
5.05      Further Action; Reasonable Efforts .......... 14
5.06      Public Announcements ........................ 14
5.07      Legend ...................................... 14


                              ARTICLE VI
                      CONDITIONS TO THE CLOSING


6.01      Conditions to Obligations of the Purchaser..  15
6.02      Conditions to Obligations of the Company....  17

                                   
                             ARTICLE VII
                           INDEMNIFICATION


7.01      Survival of Representations and Warranties... 18
7.02      Indemnification by the Company .............. 18
7.03      Indemnification by the Purchaser ............ 18
7.04      Materiality ................................. 19
7.05      Time Period; Dollar Threshold ............... 19
7.06      Notice and Defense .......................... 19

                                   
                             ARTICLE VIII
                  TERMINATION, AMENDMENT AND WAIVER

8.01      Termination ................................. 20
8.02      Effect of Termination ....................... 21
8.03      Amendment ................................... 21
8.04      Waiver ...................................... 21



                                   
                                (iii)


                                   
                              ARTICLE IX
                          GENERAL PROVISIONS

Section                                               Page
-------                                               ----

9.01      Notices ....................................  22
9.02      Entire Agreement; Assignment ...............  23
9.03      Parties in Interest ........................  23
9.04      Governing Law ..............................  23
9.05      Headings ...................................  23
9.06      Counterparts ...............................  23
9.07      Specific Performance .......................  23


EXHIBIT A  Form of Amendment No. 2 to
             the May 11, 1991 Stock Purchase Agreement


EXHIBIT B  Contents of Opinion of Wyatt, Tarrant, Combs,
             Gibert & Milan



DISCLOSURE SCHEDULE





               STOCK PURCHASE AGREEMENT (this "Agreement"), dated as of February
                                               ---------
9, 1992, between REN CORPORATION-USA, a Tennessee corporation (the "Company"),
                                                                    -------
and COBE LABORATORIES, INC., a Colorado corporation (the "Purchaser").
                                                          ---------

                                W I T N E S S E T H:
                                - - - - - - - - - -

               WHEREAS, the Company desires to authorize, issue and sell to the
Purchaser, and the Purchaser desires to purchase from the Company, the Shares
(as hereinafter defined).

               NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements hereinafter set forth, the parties hereto agree as
follows:


                               ARTICLE I

                              DEFINITIONS
                              -----------

               SECTION 1.01. Definitions. As used in this
                             -----------
Agreement, the following terms shall have the following meanings:

               "Affiliate" of a Person means a Person that, directly or
                ---------
indirectly, through one or more intermediaries, controls, is controlled by, or
is under common control with, the first mentioned Person.


               "Amendment No. 2" means the Amendment No. 2 to the Stock Purchase
                ---------------
Agreement, dated as of May 11, 1991, as amended by Amendment No. 1, dated May
24, 1991, between the Company and the Purchaser, substantially in the form of
Exhibit A hereto.

               "Bankruptcy Proceeding" has the meaning specified in Section
                ---------------------
6.01(e).

               "Board" means the Board of Directors of the Company.
                -----

               "Business Day" means any day other than a Saturday, Sunday or
                ------------
federal holiday and consists of the time period from 12:01 a.m. through 12:00
midnight, Eastern Standard Time.

               "By-Laws" means the Restated By-Laws of the Company, as amended
                -------
through the date hereof.





                                       2


               "Charter of Incorporation" means the Restated Charter of
                ------------------------
Incorporation of the Company, as amended through the date hereof.

               "Closing" means the completion of the transactions specified
                -------
herein relating to the purchase and sale of the Shares, as contemplated by
Section 2.01 hereof.

               "Closing Date" means the date on which the Closing shall occur.
                ------------

               "Common Stock" means the common shares of the Company, no par
                ------------
value.

               "Company" means REN Corporation-USA, a Tennessee corporation.
                -------

               "Company Loss" has the meaning specified in Section 7.03.
                ------------

               "control" (including the terms "controlled by" and "under common
                -------                        -------------       ------------
control with") means the possession, directly or indirectly, or as trustee or
------------
executor, of the power to direct or cause the direction of the management and/or
policies of a Person, whether through the ownership of stock, as trustee or
executor, by contract or credit arrangement, or otherwise.

               "December Balance Sheet" means the balance sheet, dated as of
                ----------------------
December 31, 1991, included in the December Financial Statements.


               "December Financial Statements" has the meaning specified in
                -----------------------------
Section 3.07(c).

               "Disclosure Schedule" means the Disclosure Schedule, dated as of
                -------------------
the date hereof, delivered to the Purchaser by the Company and forming a part of
this Agreement.

               "Encumbrance" means any security interest, pledge, mortgage, lien
                -----------
(including environmental liens), charge, adverse claim or restriction of any
kind, including, without limitation, any restriction on the use, voting,
transfer, receipt of income or other exercise of any attributes of ownership,
but excluding such Encumbrances which, taken as a whole, would not have a
Material Adverse Effect.

               "Exchange Act" means the Securities Exchange Act of 1934, as
                ------------
amended, together with the rules and regulations promulgated thereunder.





                                       3

               "First Union Loan Agreement" means the amended and restated loan
                --------------------------
agreement, dated as of March 18, 1990, between the Company and First Union
National Bank of North Carolina, a national banking association under the laws
of the United States, as such agreement has been amended, supplemented, restated
or otherwise modified from time to time, together with any notes, security
pledge, guaranty or other ancillary agreements executed pursuant thereto.

               "GAAP" means U.S. generally accepted accounting principles and
                ----
practices in effect from time to time, applied consistently throughout the
periods involved.

               "HSR Act" means the Hart-Scott-Rodino Antitrust Improvements Act
                -------
of 1976, as amended, and the rules and regulations promulgated thereunder.

               "Liabilities" means any and all debts, liabilities and
                -----------
obligations, whether accrued or fixed, absolute or contingent, mature or
unmatured, or determined or determinable, including, without limitation, those
arising under any law, rule, regulation or order by a governmental
authority, and those arising under any contract, agreement, commitment or
undertaking.

               "Loss" has the meaning specified in Section 7.03.
                ----

               "Material Adverse Effect" means any circumstance, change, event,
                -----------------------
transaction, loss, failure, effect or other occurrence that is, or is reasonably
likely to be, materially adverse to the business, operations, properties
(including intangible properties), condition (financial or otherwise), assets,
Liabilities, results of operations or prospects of the Company and its
Subsidiaries taken as a whole.

               "Person" means an individual, corporation, partnership,
                ------
association, trust, joint venture, unincorporated organization, other entity or
group (as defined in Section 13(d)(3) of the Exchange Act).

               "Purchase Price" has the meaning specified in Section 2.01.
                --------------

               "Purchaser Loss" has the meaning specified in Section 7.02.
                --------------

               "SEC" means the Securities and Exchange Commission.
                ---

               "SEC Reports" means all forms, reports and documents required to
                -----------
be filed by the Company with the SEC since November 28, 1989, including, without
limitation, (i) the





                                     4

Company's Annual Reports on Form 10-K for the fiscal years ended December 31,
1989 and 1990 and (ii) all other reports or registrations filed by the Company
with the SEC since November 28, 1989.

               "Securities Act" means the Securities Act of 1933, as amended,
                --------------
together with the rules and regulations promulgated thereunder.

               "Shares" has the meaning specified in Section 2.01.
                ------
               "Subsidiary" or "Subsidiaries" means any corporation,
                ----------      ------------
partnership, joint venture or other legal entity, of which the Company or any
other Person, as the case may be (either alone or through or together with any
other Subsidiary), owns, directly or indirectly, 50 percent or more of the stock
or other equity interests, and the holders of which are generally entitled to
vote for the election of the board of directors or other governing body of such
corporation or other legal entity.


                                  ARTICLE II

                    PURCHASE AND SALE OF SHARES; CLOSING
                    ------------------------------------

               SECTION 2.01. Authorization, Purchase and Sale of Shares. Upon
                             ------------------------------------------
the terms and subject to the conditions set forth herein, at the Closing, the
Company shall authorize, issue and sell to the Purchaser, and the Purchaser
shall purchase from the Company, 1,170,732 shares of Common Stock (such shares
of Common Stock being herein the "Shares") for an aggregate purchase price of
                                  ------
$12,000,003 (the "Purchase Price").
                  --------------

               SECTION 2.02. Closing. (a) The Closing of the purchase and sale
                             -------
shall take place within three Business Days of the satisfaction or waiver of the
conditions set forth herein, at the offices of Wyatt, Tarrant, Combs, Gilbert &
Milom, Suite 1350, Third National Bank Building, Nashville, Tennessee, or at
such other time and place as the Company and the Purchaser may mutually agree in
writing.

               (b) At the Closing, the Company shall deliver or cause to be
delivered to the Purchaser: (i) stock certificates evidencing the Shares
registered in the name of the Purchaser (or its designee); (ii) the certificate
referred to in Section 6.01(a); (iii) the legal opinion referred to in Section
6.01(g); (iv) a receipt for the Purchase Price; and (v) such other documents as
the Purchaser shall reasonably request.



                                       5

               (c) At the Closing, the Purchaser shall deliver to the Seller:
(i) the Purchase Price, by wire transfer, to an account or accounts designated
by the Company at least two Business Days prior to the Closing Date; (ii) the
certificate referred to in Section 6.02(a); (iii) a receipt for the
Shares; and (iv) such other documents as the Company shall reasonably request.


                                 ARTICLE III

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY
                  ---------------------------------------------

               The Company represents and warrants to the Purchaser that:


               SECTION 3.01. Organization and Qualification; Subsidiaries. The
                             --------------------------------------------
Company and each of its Subsidiaries are corporations duly organized, validly
existing and in good standing under the laws of their respective jurisdictions
of incorporation, and have the requisite corporate power and authority to own,
lease and operate their properties and carry on their businesses in all material
respects as presently owned or conducted. The Company and each of its
Subsidiaries are duly qualified or licensed as a foreign corporation to do
business, and are in good standing, in each jurisdiction where the character of
their properties owned, leased or operated by them, or the nature of their
activities, makes such qualification or licensing necessary, except those
jurisdictions, if any, in which the failure to be so duly qualified or licensed
and in good standing would not, taken as a whole, have a Material Adverse
Effect.  Schedule 3.01 of the Disclosure Schedule sets forth a complete and
correct list of each of the Subsidiaries of the Company.

               SECTION 3.02. Charter of Incorporation and By-Laws. The Company
                             ------------------------------------
has heretofore furnished to the Purchaser a complete and correct copy of the
Charter of Incorporation and the By-Laws, each as amended to date, each
of which is in full force and effect. The Company is not in violation of any of
the provisions of the Charter of Incorporation or By-Laws, and its Subsidiaries
are not in violation of any of the provisions of their charters of
incorporation, by-laws or equivalent organizational documents, except where such
violation would not, taken as a whole, have a Material Adverse Effect.




                                        6

               SECTION 3.03. Capitalization. (a) The authorized capital stock of
                             --------------
the Company consists of (x) 10,000,000 shares of Preferred Stock, of which none
is issued, outstanding or reserved for issuance, and (y) 60,000,000 shares of
Common Stock, of which (i) 11,210,737 shares of Common Stock are issued and
outstanding, (ii) 0 shares of Common Stock are held in the treasury of the
Company, (iii) an aggregate of 271,400 shares of Common Stock are subject to
outstanding options, and 481,125 shares are reserved for issuance, pursuant to
the Company's Stock Option Plan, (iv) an aggregate of 331,838 shares of Common
Stock are subject to outstanding promissory notes that are convertible into
shares of Common Stock, (v) 180,000 shares of Common Stock are held in escrow on
behalf of the Company and certain shareholders, in connection with a settlement
of a claim arising from an acquisition of a treatment center in Douglas,
Georgia, and (vi) an aggregate of 100,700 shares of Common Stock are subject to
outstanding warrants that are exercisable into shares of Common Stock.

               (b) Except as set forth in this Section 3.03 or in Schedule
3.03(b) of the Disclosure Schedule, there are no options, warrants or other
rights, agreements, arrangements or commitments of any character to which the
Company or any of its Subsidiaries is a party, or obligating the Company or
any of its Subsidiaries to issue or sell any shares of capital stock of, or
other equity interests in, the Company or any of its Subsidiaries. Except as set
forth in Schedule 3.03(b) of the Disclosure Schedule, there are no outstanding
contractual obligations of the Company or any of its Subsidiaries to repurchase,
redeem or otherwise acquire any of the capital stock of the Company or any
Subsidiary or to provide funds to or make any investment (in the form of a
loan, capital contribution or otherwise) in any Subsidiary or any other entity.
Each of the outstanding shares of capital stock of each of the Company's
Subsidiaries is duly authorized, validly issued, fully paid and nonassessable,
and is owned by the Company, directly or indirectly, free and clear of all
Encumbrances, except as set forth in Schedule 3.03(b) of the Disclosure
Schedule, and for any Encumbrances incurred pursuant to the First Union Loan
Agreement and Encumbrances for taxes not yet due and payable.

               (c) Except as set forth on Schedule 3.03(c) of the Disclosure
Schedule, the Company is not party to any agreement granting registration rights
to any Person with respect to any equity or debt securities of the Company.

               SECTION 3.04. Authority Relative to This Agreement. The Company
                             ------------------------------------
has all necessary corporate power and authority to execute and deliver this
Agreement, to perform




                                       7

its obligations and to consummate the transactions contemplated hereunder. The
execution, delivery and performance of this Agreement by the Company have been
duly and validly authorized by all necessary corporate action, and no other
corporate proceedings on the part of the Company are necessary to authorize this
Agreement or to consummate the transactions contemplated by this Agreement. This
Agreement has been duly and validly executed and delivered by the Company and,
assuming the due authorization, execution and delivery hereof by the Purchaser
and payment for the Shares as contemplated by this Agreement, constitutes the
legal, valid and binding obligation of the Company, enforceable against the
Company in accordance with its terms (except, in each such case, as
enforceability may be limited by bankruptcy, insolvency, reorganization and
other similar laws now or hereafter in effect relating to or affecting
creditors' rights generally, and to the extent that the remedy of specific
performance and injunctive and other forms of equitable relief are subject to
certain equitable defenses and to the discretion of the court before which any
proceeding therefor may be brought).

               SECTION 3.05. No Conflict; Required Filings and Consents. 
                             ------------------------------------------
(a) Assuming the satisfaction of the conditions set forth in Article VI hereof, 
the execution and delivery of this Agreement by the Company do not, and the
performance of this Agreement (including, without limitation, the consummation
of the transactions contemplated hereunder) will not, (i) conflict with or
violate the Charter of Incorporation or By-Laws, (ii) conflict with or violate
the charters of incorporation or by-laws or equivalent organizational documents
of any of the Company's Subsidiaries, (iii) conflict with or violate any law,
rule, regulation, order, judgment or decree applicable to the Company or any of
its Subsidiaries or by which the Company or any of its Subsidiaries respective
properties are bound or affected, or (iv) result in any breach of, or constitute
a default (or an event which, with notice or lapse of time or both, would become
a default) under, or give to others any rights of termination, amendment,
acceleration or cancellation of, or result in the creation of a lien or
encumbrance on any of the properties or assets of the Company or any of its
Subsidiaries pursuant to, any note, bond, mortgage, indenture, contract,
agreement, lease, license, permit, insurance policy or other instrument or
obligation to which the Company or any of its Subsidiaries is a party, or by
which the Company or any of its Subsidiaries or its or any of their respective
properties are bound or affected, except, in the case of clauses (ii), (iii) and
(iv) above, for such conflicts which would not, taken as a whole, have a
Material Adverse Effect.





                                        8

               (b) The execution and delivery of this Agreement by the Company
do not, and the performance of this Agreement by the Company (including, without
limitation, the consummation of the transactions hereunder) will not, require
any consent, approval, authorization or permit of, or filing (other than
filings, if any, required on Form 8-K with the SEC and pursuant to the HSR Act)
with, or notification to, any third party or any governmental or regulatory
authority, domestic or foreign, on the part of the Company or any of its
Subsidiaries.

               SECTION 3.06. Common Stock. Assuming all conditions set forth in
                             ------------
Article VI are satisfied, following the consummation of the transactions
hereunder, all of the Shares subject to issuance pursuant to this Agreement,
upon such issuance against payment for such Shares as contemplated by this
Agreement, shall (i) be duly authorized, validly issued, fully paid and
nonassessable and (ii) not be subject to any Encumbrances (other than those that
may be incurred by the Purchaser). The Shares shall have accorded to them full
voting rights. None of the Shares are "Control Shares", as such term is defined
in the Tennessee Business Corporation Act.

               SECTION 3.07. SEC Filings; Financial Statements. (a) The Company
                             ---------------------------------
has filed all forms, reports, statements and documents required to be filed with
the SEC since November 28, 1989, including, without limitation, the SEC Reports.
The SEC Reports (i) were each prepared in accordance with, and, at the time of
filing, complied in all material respects with, the requirements of the
Securities Act or the Exchange Act, as the case may be, and (ii) did not, at the
time they were filed, contain any untrue statement of a material fact or omit to
state a material fact required to be stated therein or necessary in order to
make the statements therein, in the light of the circumstances under which they
were made, not misleading. None of the Company's Subsidiaries is required to
file any forms, reports or other documents with the SEC.

               (b) Each of the consolidated financial statements (including, in
each case, any related notes thereto) contained in the SEC Reports has been
prepared in accordance with GAAP (except as may be indicated in the notes
thereto), and each presents fairly the consolidated financial position of the
Company and its consolidated Subsidiaries at the respective dates thereof and
the consolidated results of its operations and changes in cash flows for the
periods




                                       9

indicated, except that the unaudited interim financial statements were or are
subject to normal and recurring year-end adjustments, which were not and are not
expected to be material in amount.

               (c) Schedule 3.07(c) of the Disclosure Schedule hereto sets forth
the unaudited consolidated balance sheet of the Company and its Subsidiaries and
the unaudited statement of operations for the 12-month period ended December 31,
1991 (the "December Financial Statements"). The December Financial Statements
           -----------------------------
have been prepared in accordance with GAAP and present fairly the financial
condition of the Company and its consolidated Subsidiaries as of December 31,
1991 and the consolidated results of its operations for the 12-month period
ended December 31, 1991, except that the December Financial Statements are
subject to normal or recurring year-end adjustments, which are not expected to
be material in amount.

               (d) Except as set forth in Schedule 3.07(d) of the Disclosure
Schedule hereto and as and to the extent set forth on the December Financial
Statements, neither the Company nor any of its Subsidiaries has any Liabilities,
including, without limitation, liabilities for taxes which would be
required to be reflected on a balance sheet, or in the notes thereto prepared in
accordance with GAAP, except for liabilities or obligations incurred in the
ordinary course of business since December 31, 1991 which would not, taken as a
whole, have a Material Adverse Effect.

               SECTION 3.08. Private Offering. (a) Assuming the accuracy of the
                             ----------------
representations and warranties of the Purchaser, the sale of the Shares
hereunder is exempt from the registration and prospectus delivery requirements
of the Securities Act.

               (b) No form of general solicitation or general advertising
(including, without limitation, advertisements, articles, notices or other
communications published in any newspaper, magazine or other medium or broadcast
over television or radio, or any seminar or meeting whose attendees have been
invited by any general solicitation or general advertising) was used by the
Company or any other Person acting on behalf of the Company in respect of the
Shares or in connection with the offer and sale of the Shares.


                                      10

               SECTION 3.09. Brokers. No broker, finder or investment banker is
                             -------
entitled to any brokerage, finder's or other fee or commission in connection
with the transactions hereunder based upon arrangements made by or on behalf of
the Company.


                                   ARTICLE IV

                   REPRESENTATIONS AND WARRANTIES OF THE PURCHASER
                   -----------------------------------------------

               The Purchaser represents and warrants to the Company that:

               SECTION 4.01. Corporate Organization. The Purchaser is a
                             ----------------------
corporation duly organized, validly existing and in good standing under the laws
of Colorado and has the requisite corporate power and authority and any
necessary governmental authority to own, operate or lease the properties that it
purports to own, operate or lease and to carry on its business as it is now
being conducted.

               SECTION 4.02. Authority Relative to This Agreement. The Purchaser
                             ------------------------------------
has all necessary corporate power and authority to execute and deliver this
Agreement and to perform its obligations and to consummate the transactions
contemplated hereunder. The execution and delivery of this Agreement by the
Purchaser and the purchase of the Shares as provided in Section 2.01 hereof by
the Purchaser hereunder have been duly and validly authorized by all necessary
corporate action of the Purchaser and no other corporate proceedings on the part
of the Purchaser are necessary to authorize this Agreement or the purchase of
the Shares by the Purchaser as contemplated hereby. This Agreement has been
duly and validly executed and delivered by the Purchaser and, assuming the due
authorization, execution and delivery by the Company, constitutes the legal,
valid and binding obligation of the Purchaser enforceable against the Purchaser
in accordance with its terms (except in each such case as enforceability may be
limited by bankruptcy, insolvency, reorganization and other similar laws now or
hereafter in effect relating to or affecting creditors' rights generally and to
the extent that the remedy of specific performance and injunctive and other
forms of equitable relief are subject to certain equitable defenses and to the
discretion of the court before which any proceeding therefor may be brought),



                                       11

               SECTION 4.03. No Conflict; Required Filings and Consents. (a) The
                             ------------------------------------------
execution and delivery of this Agreement by the Purchaser do not, and the
performance of this Agreement by the Purchaser will not, (i) conflict with or
violate the articles of incorporation or by-laws or equivalent organizational
documents of the Purchaser, (ii) conflict with or violate any law, rule,
regulation, order, judgment or decree applicable to the Purchaser or by which it
or its properties are bound or affected, or (iii) result in any breach of or
constitute a default (or an event which with notice or lapse of time or both
would become a default) under, or give to others any rights of termination,
amendment, acceleration or cancellation of, or result in the creation of a lien
or encumbrance on any of the property or assets of the Purchaser pursuant to,
any note, bond, mortgage, indenture, contract, agreement, lease, license,
permit, franchise or other instrument or obligation to which the Purchaser is a
party or by which the Purchaser or any of its properties is bound or affected,
except, in the case of this clause (iii) and clause (ii) above, for any such
breaches, defaults or other occurrences which would not, individually or in the
aggregate, have a material adverse effect on the business, operations,
properties (including intangible properties), condition (financial or
otherwise), assets or liabilities of the Purchaser.

               (b) The execution and delivery of this Agreement by the Purchaser
do not, and the performance of this Agreement by the Purchaser (including,
without limitation, the consummation of the transactions hereunder) will not,
require any consent, approval, authorization or permit of, or filing (other
than a filing pursuant to the HSR Act) with or notification to, any third party
or any governmental or regulatory authority, domestic or foreign.

               SECTION 4.04. Funds. The Purchaser has and, immediately prior to
                             -----
the Closing, will have the funds necessary to consummate the purchase of the
Shares hereunder.

               SECTION 4.05. Securities Act. The Shares purchased by the
                             --------------
Purchaser pursuant to this Agreement are being acquired for investment only and
not with a view to any sale or distribution (within the meaning of the
Securities Act) of the Shares or any part thereof. The Purchaser agrees at all
times to sell or otherwise dispose of all or any part of the Shares so acquired
by the Purchaser (and any securities issued in exchange therefor) only pursuant
to a registration, or exemption therefrom, under the Securities Act and in


                                   12

compliance with applicable state securities laws. The Purchaser will take any
steps necessary to insure that any purchaser will agree not to sell or otherwise
dispose of Shares except in compliance with the requirements contained in the
preceding sentence. The Purchaser is an "accredited investor" within the meaning
of Rule 501 promulgated under the Securities Act and has such knowledge and
experience in financial and business matters as to be capable of evaluating the
merits and risks of an investment in the Shares. The Purchaser has received all
the information it deems material to its evaluation of the business, assets,
liabilities, financial condition and results of operations of the Company and
all the information it has requested from the Company and considers necessary or
appropriate for deciding whether to purchase the Shares. The Purchaser has the
ability to bear the economic risks of the Purchaser's prospective investment and
the Purchaser is able, without materially impairing its financial
condition, to hold the Shares for an indefinite period of time and to suffer
complete loss on its investment. The Purchaser understands and has fully
considered for purposes of this investment the risks of this investment and
understands that: (i) this investment is suitable only for an investor who is
able to bear the economic consequences of losing his or its entire investment;
(2) the Shares represent an extremely speculative investment which involves a
high degree of risk of loss; (3) there are substantial restrictions on the
transferability of the Shares and, accordingly, it may not be possible for the
Purchaser to liquidate his or its investment in the Shares in case of emergency;
and (4) there have been no representations as to the possible future value, if
any, of the Shares.

               The Purchaser understands and acknowledges that the sale of the
Shares pursuant to this Agreement will not be registered under the Securities
Act on the grounds that the offering and sale of securities contemplated by this
Agreement are exempt from registration pursuant to Section 4(2) of the
Securities Act, and that the Company's reliance upon such exemption is
predicated in part upon the Purchaser's representations set forth in this
Agreement.

               SECTION 4.06. Brokers. No broker, finder or investment banker is
                             -------
entitled to any brokerage, finder's or other fee or commission in connection
with the transactions hereunder based upon arrangements made by or on behalf of
the Purchaser.





                                       13

                                   ARTICLE V

                             ADDITIONAL AGREEMENTS
                             ---------------------

               SECTION 5.01. Conduct of Business by the Company Pending the
                             ----------------------------------------------
Closing. Except as contemplated by this Agreement, the Company covenants and
-------
agrees that, during the period between the date of this Agreement and through
and including the Closing Date, unless the Purchaser shall otherwise agree in
writing, the businesses of the Company and its Subsidiaries shall be conducted
only in, and the Company and its Subsidiaries shall not take any action except
in, the ordinary course of business and in a manner consistent with past
practice.

               SECTION 5.02. Regulatory and Other Authorizations. Each party
                             -----------------------------------
hereto will use its reasonable best efforts to obtain all authorizations,
consents, orders and approvals of all third parties and of all federal, state
and local regulatory bodies and officials that may be or become necessary for
its execution and delivery of, and the performance of its obligations pursuant
to, this Agreement and will cooperate fully with the other party in promptly
seeking to obtain all such authorizations, consents, orders and approvals. Each
party hereto agrees to make, or cause its "ultimate parent entity" (as such term
is defined in the HSR Act) to make, an appropriate filing of a Notification and
Report Form pursuant to the HSR Act with respect to the transactions
contemplated hereby within ten Business Days of the date hereof. The parties
hereto will not take any action that will have the effect of delaying, impairing
or impeding the receipt of any required approvals.

               SECTION 5.03 Access to Information. (a) From the date hereof to
                            ---------------------
the Closing Date, the Company shall, and shall cause its Subsidiaries, officers,
directors, employees, auditors and other agents to, afford the officers,
employees, auditors and other agents of the Purchaser reasonable access at all
reasonable times to its officers, employees, agents, properties, offices, plants
and other facilities and to all books and records, and shall furnish the
Purchaser with all financial, operating and other data and information with
respect to the business and properties of the Company as the Purchaser, through
its officers, employees or agents, may reasonably request. The Purchaser agrees
to maintain the strict confidentiality of such data and information and not to
disclose such data to any third party.




                                      14

               (b) No investigation pursuant to this Section 5.03 shall affect
any representations or warranties of the parties herein or the conditions to the
obligations of the parties hereto.

               SECTION 5.04. Notification of Certain Matters. The Company shall
                             -------------------------------
give prompt notice to the Purchaser, and the Purchaser shall give prompt notice
to the Company, of (i) the occurrence, or non-occurrence, of any event the
occurrence, or non-occurrence, of which would be likely to cause any
representation or warranty contained in this Agreement to be untrue or
inaccurate and (ii) any failure of the Company or the Purchaser, as the case may
be, to comply with or satisfy any covenant, condition or agreement to be
complied with or satisfied by it hereunder; provided, however, that the delivery
                                            --------  -------
of any notice pursuant to this Section 5.04 shall not limit or otherwise affect
the remedies available hereunder to the party receiving such notice.

               SECTION 5.05. Further Action; Reasonable Efforts. Upon the terms
                             ----------------------------------
and subject to the conditions hereof, each of the parties hereto shall use all
reasonable efforts to take, or cause to be taken, all appropriate action, and to
do or cause to be done all things necessary, proper or advisable under
applicable laws and regulations to consummate and make effective the
transactions contemplated hereunder.

               SECTION 5.06. Public Announcements. The Purchaser and the Company
                             --------------------
shall consult with each other before issuing any press release or otherwise
making any public statements with respect to the transactions contemplated
hereunder and shall not issue any such press release or make any such public
statement prior to such consultation, except as may be, and to the extent,
required by law or any listing agreement with the National Association of
Securities Dealers.

               SECTION 5.07. Legend. The Purchaser agrees that all certificates
                             ------
representing the Shares issued pursuant to this Agreement shall bear the
following legend:

                "THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
        REGISTERED UNDER THE SECURITIES ACT OF 1933 OR SECURITIES LAWS OF ANY
        STATE AND NEITHER THE SECURITIES NOR ANY INTEREST THEREIN MAY BE SOLD OR
        OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN
        EXEMPTION THEREUNDER. THE SHARES REPRESENTED BY THIS CERTIFICATE ARE
        SUBJECT (IN CERTAIN CIRCUMSTANCES) TO A RIGHT OF FIRST OFFER AS SET
        FORTH IN THE STOCK PURCHASE AGREEMENT DATED AS OF MAY 11, 1991, AS
        AMENDED, BETWEEN THE COMPANY AND COBE LABORATORIES, INC."




                                       15


                                   ARTICLE VI


                           CONDITIONS TO THE CLOSING
                           -------------------------

              SECTION 6.01. Conditions to Obligations of the Purchaser. The
                            ------------------------------------------
obligations of the Purchaser to effect the Closing shall be subject to the prior
fulfillment of each of the following conditions:

                (a) Representations and Warranties; Agreements and Covenants.
                    --------------------------------------------------------
         Except for changes permitted or contemplated hereby or consented to by
         the Purchaser and  except for matters waived or consented to by the
         Purchaser pursuant to Section 8.04, (i) the representations and
         warranties of the Company contained in this Agreement which are
         qualified as to materiality shall be true in all respects and all other
         representatives and warranties shall be true and correct in all
         material respects on and as of the Closing, with the same force and
         effect as if made as of the Closing, (ii) all the agreements contained
         in this Agreement to be performed or complied with by the Company, at
         or before the Closing, shall have been performed or complied with in
         all material respects and (iii) the Purchaser shall have received a
         certificate of the Company, signed by the Chief Executive Officer
         thereof, as to the fulfillment of the conditions set forth in the
         foregoing clauses (i) and (ii).

                (b) No Cessation Order. No order, ruling or determination
                    ------------------
         having the effect of halting the trading of the Common Stock shall have
         been issued or made by the SEC or other regulatory authority and be
         continuing and no proceedings for that purpose shall have been
         instituted and be pending.

                (c) Litigation. There shall have been no order or preliminary
                    ----------
         or permanent injunction entered in any action or proceeding before any
         federal, state or foreign court or governmental, administrative or
         regulatory authority or agency, or no other action taken or threatened,
         or statute, rule, regulation, legislation, interpretation, judgment or
         order enacted, entered, enforced, promulgated, amended, issued or
         deemed applicable to the Purchaser, the Company or any Subsidiary or
         Affiliate of the Purchaser, by any federal, state or foreign
         legislative body, court, government or governmental, administrative or
         regulatory authority or agency which


                                      16

         shall have remained in effect and which shall have had the effect of:
         (i) making illegal, materially delaying or otherwise directly or
         indirectly restraining or prohibiting the consummation of the
         transactions hereunder; (ii) prohibiting or materially limiting the
         ownership of the Shares; (iii) imposing material limitations on the
         ability of the Purchaser to exercise full rights of ownership
         of any of the Shares, including, without limitation, the right to vote
         any shares of Common Stock; or (iv) requiring divestiture by the
         Purchaser of any Shares.

                 (d) Calamities. There shall not have occurred and be continuing
                     ----------
         (i) any general suspension of, or limitation on prices for or trading
         in, securities on any United States securities exchange, {ii) a
         declaration of a banking moratorium or any suspension of payments in
         respect of banks in the United States, (iii) any limitation (whether or
         not mandatory) by any government or governmental, administrative or
         regulatory authority or agency, domestic or foreign, or other event
         that materially adversely affects the ability of the Purchaser to
         purchase the Shares hereunder, or (iv) a commencement of a war or
         armed hostilities or other national or international calamity directly
         involving the United States or Sweden.

                 (e) Bankruptcy; Insolvency; Etc. No proceeding shall have been
                     ----------------------------
         instituted or consented to by or against the Company seeking to
         adjudicate it bankrupt or insolvent, or seeking liquidation, winding-
         up, reorganization, arrangement, adjustment, protection, relief, or
         composition of its debts under any law relating to bankruptcy,
         insolvency or reorganization or relief of debtors, or seeking the entry
         of an order for relief or the appointment of a receiver, trustee,
         custodian or other similar official for it or any substantial part of
         its property (each such action being a "Bankruptcy Proceeding"), and
                                                 ---------------------
         the Company shall not have taken any corporate action to authorize any
         Bankruptcy Proceeding.

                 (f) No Material Adverse Effect. No fact, event or condition
                     --------------------------
         (financial or otherwise) shall have occurred with respect to the
         Company or any of its Subsidiaries having, individually or in the
         aggregate, a Material Adverse Effect.



                                      17

                (g) Opinion. The Purchaser shall have received an opinion from
                    -------
         Wyatt, Tarrant, Combs, Gibert & Milan substantially to the effect of
         Exhibit B hereto.

                (h) Amendment No. 2. Amendment No. 2 shall have been executed
                    ---------------
         and delivered by the Company.

                (i) HSR Act. Any waiting period (and any extension thereof)
                    -------
         under the HSR Act applicable to the purchase of the Shares contemplated
         hereby shall have expired or shall have been terminated.

                SECTION 6.02. Conditions to Obligations of the Company. The
                              ----------------------------------------
obligations of the Company to effect the Closing shall be subject to the prior
fulfillment of each of the following conditions:

                (a) Representations and Warranties. (i) The representations and
                    ------------------------------
         warranties of the Purchaser contained in this Agreement and in any
         certificates or agreements of the Purchaser delivered pursuant hereto
         shall be true and correct in all material respects on and as of the
         Closing, with the same force and effect as if made as of the Closing,
         (ii) all the agreements contained in this Agreement and in any
         certificates or agreements of the Purchaser delivered pursuant hereto
         to be performed or complied with by the Purchaser, at or before
         the Closing, shall have been performed or complied with in all material
         respects and (iii) the Company shall have received a certificate of the
         Purchaser, signed by a duly authorized officer thereof, as to the
         fulfillment of the conditions set forth in the foregoing clauses (i)
         and (ii).

                (b) Litigation. There shall have been no order or preliminary
                    ----------
         or permanent injunction entered in any action or proceeding before any
         federal, state or foreign court or governmental, administrative or
         regulatory authority or agency by any federal, state or foreign
         legislative body, court, government or governmental, administrative or
         regulatory authority or agency which shall have remained in effect and
         which shall have had the effect of making illegal the consummation of
         any of the transactions hereunder.




                                     18

                (c) HSR Act. Any waiting period (and any extension thereof)
                    -------
         under the HSR Act applicable to the purchase of the Shares contemplated
         hereby shall have expired or shall have been terminated.


                                  ARTICLE VII
                                INDEMNIFICATION

                SECTION 7.01. Survival of Representations and Warranties. The
                              ------------------------------------------
representations and warranties of the Company in Article III shall survive the
Closing until the date 15 months from the Closing Date. Neither the period of
survival nor the liability of any party with respect to the parties'
representations and warranties shall be reduced by any investigation made at any
time by or on behalf of any party.

                SECTION 7.02. Indemnification by the Company. The Purchaser, and
                              ------------------------------
its Affiliates, officers, directors, employees, agents, successors and assigns,
shall be indemnified and held harmless by the Company for any and all
Liabilities, losses, damages, claims, costs and expenses, interest, awards,
judgments and penalties (including, without limitation, legal costs and
expenses) actually suffered or incurred by them (hereinafter, a "Purchaser
                                                                 ---------
Loss"), arising out of or resulting from:
----

                (a) the breach of any representation or warranty made by the
         Company contained herein or in any document delivered by the Company
         hereunder at the Closing; or

                (b) the breach of any covenant or agreement by the Company
         contained herein.

                SECTION 7.03. Indemnification by the Purchaser. The Company, and
                              --------------------------------
its Affiliates, officers, directors, employees, agents, successors and assigns,
shall be indemnified and held harmless by the Purchaser for any and all
Liabilities, losses, damages, claims, costs and expenses, interest, awards,
judgments and penalties (including, without limitation, legal costs and
expenses) actually suffered or incurred by them (hereinafter, a "Company Loss"
                                                                 ------------
and, together with a Purchaser Loss, a "Loss"), arising out of or resulting
                                        ----
from:




                                       19

                (a) the breach of any representation or warranty made by the
         Purchaser contained herein or in any document delivered by the
         Purchaser hereunder at the Closing; or

                (b) the breach of any covenant or agreement by the Purchaser
         contained herein.

                SECTION 7.04. Materiality. Notwithstanding anything in this
                              -----------
Agreement to the contrary, for purposes of application of the indemnity
provisions of this Article VII, the amount of any Purchaser Loss or Company Loss
arising from the breach of such representation, warranty, covenant or agreement
shall be the entire amount of any such Loss actually incurred by the party being
indemnified hereunder as a result of such breach and not just that portion of
such Loss that exceeds the relevant level of materiality.

                SECTION 7.05. Time Period; Dollar Threshold. (a) The
                              -----------------------------
indemnification obligations of the Company and the Purchaser under this Article
VII shall continue for the same period of survival specified in Section 7.01 for
each such representation and warranty and shall terminate with the expiration of
the 15 month survival period for each such representation and warranty. Any
claim or demand against the Company or the Purchaser which is pending or
asserted at or prior to the expiration of any survival period may continue to be
asserted and indemnified against.

                (b) Neither the Company nor the Purchaser shall be entitled to
indemnification under this Article VII unless and until the aggregate amount of
the claims against the other party exceeds $1,000,000. If the aggregate amount
of such claims against either party exceeds $1,000,000, then that party may
claim indemnification for the entire aggregate amount of such claims.

                (c) The provisions of this Article VII shall be the sole and
exclusive remedy (other than injunctive relief) of the Company or the Purchaser
(regardless of against whom asserted) for the matters subject to
indemnification.

                SECTION 7.06. Notice and Defense. Each party shall within 30
                              ------------------
days of learning of any asserted liability or damage claimed to give rise to
indemnification hereunder notify the party obligated to indemnify it hereof in
writing; provided, however, that the failure of the indemnified party to so
         --------  -------
notify the indemnifying party shall not relieve the indemnifying party of its
obligations hereunder unless, and


                                       20

only to the extent that, such failure to notify prejudices the indemnifying
party. Thereafter, the indemnifying party shall have, at its election, the right
to compromise or defend any such matter at its sole cost and expense through
counsel chosen by it. If the indemnifying party so undertakes to compromise and
defend, the indemnifying party shall notify the other party of its intention to
do so. The indemnifying party must defend such matter diligently or the
indemnified party may assume control of the defense of such matter. Each party
agrees in all cases to cooperate with the defending party and its counsel in the
compromise of or defending of any such liabilities or claims. The defending
party and the nondefending party may be represented by the same counsel unless
such representation would be inappropriate due to actual or potential differing
interests between them. In addition, the nondefending party shall at all times
be entitled to monitor such defense through the appointment of counsel of its
own choosing, at its own cost and expense.

                                  ARTICLE VIII

                       TERMINATION, AMENDMENT AND WAIVER
                       ---------------------------------

                SECTION 8.01. Termination. (a) This Agreement may be terminated
                              -----------
and the transactions contemplated hereby may be abandoned at any time prior to
the Closing Date:

                (i) By mutual written consent duly authorized by the Boards of
        Directors of the Company and the Purchaser; or

                (ii) By the Purchaser, if (A) (1) any Person, other than the
        Purchaser, shall have acquired, or shall have been granted any option or
        right, conditional or otherwise, to acquire beneficial ownership of 20%
        or more of the outstanding shares of the Company's Common Stock, or (2)
        any group (other than a group including the Purchaser) shall have been
        formed which beneficially owns 20% or more of the outstanding shares of
        the Company's Common Stock; or (B) the Company shall have entered into
        an agreement with a third party with respect to any acquisition or
        purchase of all or a substantial portion of the assets of, or any equity
        interest in, the Company or any of its Subsidiaries or any business
        combination with the Company or any of its Subsidiaries by such third
        party; or




                                       21

                (iii) By the Purchaser or the Company, if any court of competent
        jurisdiction in the United States or other United States governmental
        authority shall have issued an order, decree or ruling or taken any
        other action restraining, enjoining or otherwise prohibiting any of the
        transactions hereunder and such order, decree, ruling or other action
        shall have become final and nonappealable; or

                (iv)  By the Purchaser or the Company, if the Closing shall not
        have occurred by April 30, 1992 or such later date as the Company and
        the Purchaser shall hereafter agree; provided, however, that the right
                                             --------  -------
        to terminate this Agreement under this Section 8.01(a)(iv) shall not be
        available to any party whose willful failure to fulfill any material
        obligation under this Agreement has been the cause of, or resulted in,
        the failure of the Closing to occur on or before such date.

                (b) This Agreement shall terminate (without any action or notice
(in writing or otherwise) by any of the parties hereto) if any Bankruptcy
Proceeding shall have been instituted or consented to by or against the Company.

                SECTION 8.02. Effect of Termination. In the event of the
                              ---------------------
termination of this Agreement pursuant to Section 8.01, this Agreement shall
forthwith become void and have no effect and there shall be no liability on the
part of any party hereto or its Affiliates, directors, officers or
shareholders; provided, however, that nothing herein shall relieve any party
              --------  -------
from liability for any breach hereof prior to such termination.

                SECTION 8.03. Amendment. This Agreement may be amended by the
                              ---------
parties hereto by action taken by or on behalf of the Company and the Purchaser
at any time prior to the Closing Date. This Agreement may not be amended except
by an instrument in writing signed by the parties hereto.

                SECTION 8.04. Waiver. At any time prior to the Closing Date,
                              ------
either party hereto may (a) extend the time for the performance of any of the
obligations or other acts of the other party hereto, (b) waive any inaccuracies
in the representations and warranties contained herein or in any document
delivered pursuant hereto and (c) waive compliance with any of the agreements or
conditions contained herein. Any such extension or waiver shall be valid if set
forth in an instrument in writing signed by the party to be bound




                                       22

thereby. The failure of either party to assert any of its rights hereunder shall
not constitute a waiver of any such rights.


                                   ARTICLE IX

                               GENERAL PROVISIONS
                               ------------------

               SECTION 9.01. Notices. All notices, requests, claims, demands and
                             -------
other communications hereunder shall be in writing and shall be given (and shall
be deemed to have been duly given upon receipt) by delivery in person, by
cable, telecopy, telegram or telex or by registered or certified mail (postage
prepaid, return receipt requested) to the respective parties at the following
addresses (or at such other address for a party as shall be specified by like
notice):


                (a) if to the Purchaser:

                    Cobe Laboratories, Inc.
                    1185 Oak Street
                    Lakewood, Colorado 80215
                    Attention: Mats Wahlstrom

                with a copy to:

                    Shearman & Sterling
                    599 Lexington Avenue
                    New York, New York 10022
                    Attention: Peter D. Lyons, Esq.


                (b) if to the Company:

                    REN Corporation-USA
                    6820 Charlotte Pike
                    Nashville, Tennessee 37209
                    Attention: Jerome S. Tannenbaum, M.D., C.E.O.

                with a copy to:

                    Wyatt, Tarrant, Combs, Gilbert & Milom
                    Suite 1350
                    Third National Bank Building
                    Nashville, Tennessee 37219
                    Attention: Ralph Levy, Esq.





                                        23

                SECTION 9.02. Entire Agreement; Assignment. This Agreement
                              ----------------------------
constitutes the entire agreement between the parties with respect to the subject
matter hereof and supersedes all prior agreements and undertakings, both written
and oral, between the parties with respect to the subject matter hereof. This
Agreement shall not be assigned by operation of law or otherwise, except that
the Purchaser may assign all or any of its rights and obligations hereunder to
any wholly owned Subsidiary of Gambro Aktiebolag, the owner of all the
outstanding capital stock of the Purchaser, upon the execution of a written
instrument whereby such assignee agrees to assume all of the Purchaser's
obligations hereunder and be bound by all the terms and conditions of this
Agreement; provided that no such assignment shall relieve the Purchaser of its
           --------
obligations hereunder if such assignee does not perform such obligations.

                SECTION 9.03. Parties in Interest. This Agreement shall be
                              -------------------
binding upon and inure solely to the benefit of each party hereto, and nothing
in this Agreement, express or implied, is intended to or shall confer upon any
other person any rights, benefits or remedies of any nature whatsoever under or
by reason of this Agreement.

                SECTION 9.04. Governing Law. This Agreement shall be governed
                              -------------
by, and construed in accordance with, the laws of the State of New York,
regardless of the laws that might otherwise govern under applicable principles
of conflicts of laws thereof.

                SECTION 9.05. Headings. The descriptive headings contained in
                              --------
this Agreement are included for convenience of reference only and shall not
affect in any way the meaning or interpretation of this Agreement.

                SECTION 9.06. Counterparts. This Agreement may be executed in
                              ------------
one or more counterparts, and by the different parties hereto in separate
counterparts, each of which when executed shall be deemed to be an original but
all of which taken together shall constitute one and the same agreement.

                SECTION 9.07. Specific Performance. The parties hereto agree
                              --------------------
that irreparable damage would occur in the event any of the provisions of this
Agreement were not to be performed in accordance with the terms hereof and that
the parties shall be entitled to specific performance of the



                                       24

terms hereof, in addition to any other remedy at law or equity.

                IN WITNESS WHEREOF, the Purchaser and the Company have each
caused this Agreement to be executed by its duly authorized officer as of the
date first written above.


                                        COBE LABORATORIES, INC.

                                        By
                                        ------------------------------
                                        Name: Mats Wohlstrom
                                        Title: President



                                        REN CORPORATION-USA



                                        By
                                        ------------------------------
                                        Name: Jerome S. Tannenbaum
                                        Title: Chief Executive Officer






                                                                       EXHIBIT A
                                                                       ---------


                         FORM OF AMENDMENT NO. 2 TO THE
                     MAY 11, 1991 STOCK PURCHASE AGREEMENT


                AMENDMENT NO. 2, dated as of __________, 1992 (this "Amendment")
                                                                     ---------
to the  Stock Purchase Agreement, dated as of May 11, 1991, as amended by
Amendment No. 1, dated as of May 24, 1991, between REN CORPORATION-USA, a
Tennessee  corporation (the "Company") and COBE LABORATORIES, INC., a Colorado
                             -------
corporation (the "Purchaser").
                  ---------

                              W I T N E S S E T H
                              - - - - - - - - - -


               WHEREAS, the Company and the Purchaser have entered into as of
May 11, 1991 a Stock Purchase Agreement (the "Purchase Agreement"; capitalized
                                              ------------------
terms used and not defined herein being used herein as defined in the Purchase
Agreement);

               WHEREAS, the Company and the Purchaser entered into on May 24,
1991 an Amendment No. 1 to the Purchase Agreement; and

               WHEREAS, the Company and the Purchaser have determined that it is
in their mutual interests to further amend the Purchase Agreement as hereinafter
set forth.

               NOW THEREFORE, in consideration of the premises and of the mutual
agreements and understandings hereinafter set forth, the Purchaser and the
Company agree as follows:

               SECTION 1. Amendments to the Purchase Agreement. The Purchase
                          ------------------------------------
Agreement is, effective as of the date hereof, hereby amended as follows:

                (a) New defined terms shall be added to Section 1.01,
         immediately following the definition of "Affiliate", to read as
         follows:

                "'Amendment No. 1' means the Amendment No. 1, dated May 24,
                  ---------------
        1991, to this Agreement between the Company and the Purchaser.

                'Amendment No. 2' means the Amendment No. 2, dated _______,
                 ---------------
        1992, to this Agreement between the Company and the Purchaser."

                (b) The defined term "Purchase Agreement" shall be restated in
         full to read as follows:




                "'Purchase Agreement' means this Agreement, as amended by
                  ------------------
         Amendment No. 1 and Amendment No. 2."

        (c) Sections 5.08(a) and (b) shall be restated in full to read as
follows:

                "(a) The Company agrees, effective upon the Closing Date, to
        decrease the size of the Board to seven directors and to appoint to the
        Board two persons designated by the Purchaser (members of the Board
        designated by the Purchaser pursuant to this Section 5.08 are referred
        to as the "Purchaser's Directors"), one with his original term expiring
                   ---------------------
        at the Company's 1992 annual stockholders' meeting and the other with
        his original term expiring at the Company's 1993 annual stockholders'
        meeting. Without the prior written consent of the Purchaser, the
        Company, acting through the Board, shall not increase the size of the
        Board beyond seven members.

                (b) Effective on the Closing Date and so long as the Purchaser
        owns at least 20% of the issued and outstanding Common Stock, the
        Purchaser shall have the right to request that the Company include (x)
        one person designated by the Purchaser as a nominee to serve as a member
        of the "Class Three Directors" (as such term is used in the By-Laws;
        provided that for purposes of this Agreement, such term shall be further
        --------
        defined to be that class of directors of the Board whose term next
        expires at the 1992 annual stockholders' meeting) of the Board and (y)
        one person designated by the Purchaser to serve as a member of the
        "Class One Directors" (as such term is used in the By-Laws; provided
                                                                    --------
        that for purposes of this Agreement, such term shall be further defined
        to be that class of directors of the Board whose term next expires at
        the 1993 annual stockholders' meeting) of the Board, and such persons
        shall be nominated by the Company. In the event the Purchaser owns 15%
        or more but less than 20% of the issued and outstanding Common Stock,
        the Purchaser shall have the right to request that the Company include
        one person designated by the Purchaser as a nominee to serve as a member
        of either the Class Three Directors or the Class One Directors of the
        Board, and such person shall be nominated by the Company. If the Board,
        in the exercise of its fiduciary duties, reasonably shall determine that
        any person designated by the Purchaser to be a nominee to the Board
        pursuant to this Section 5.08




                                        3

        is not qualified to serve on the Board and each of the committees
        specified in subsection (d) of this Section 5.08, the Purchaser shall
        have the opportunity to specify one or more additional designees who
        shall be so included as a nominee subject to the reasonable
        determination by the Board, in the exercise of their fiduciary duties,
        that any such additional designee is not qualified to serve on the Board
        and each of the committees specified in this Section 5.08. The Board
        shall recommend to the stockholders of the Company for election the
        designees of the Purchaser who are nominated by the Company to serve as
        members of the Board. In the event that a vacancy is created on the
        Board at any time by the death, disability, retirement, resignation or
        removal (with or without cause) of a Purchaser's Director, the Purchaser
        shall have the right to select a nominee to fill such vacancy. If the
        remaining Board members, in the exercise of their fiduciary duties,
        reasonably shall determine that such nominee is not qualified to serve
        on the Board and each of the committees specified in subsection (d) of
        this Section 5.08, the Purchaser shall have the opportunity to select
        one or more additional nominees. Subject to the qualification set forth
        in the immediately preceding sentence, the remaining members of the
        Board shall elect to the Board to fill such vacancy any such nominee of
        the Purchaser."

        (d) The second sentence of Section 5.10(b) shall be restated in full to
read as follows:

        "The Purchaser shall have the option to purchase from the Company
        additional shares of Common Stock to the extent necessary to permit the
        Purchaser to maintain 30% of the issued and outstanding shares of Common
        Stock and 30% of the Total Voting Power."

        SECTION 2. Counterparts. This Amendment may be executed in one or
                   ------------
more counterparts, and by the different parties hereto in separate counterparts,
each of which when executed shall be deemed to be an original, but all of which
taken together shall constitute one and the same agreement.

        SECTION 3. Governing Law. This Amendment shall be governed by,
                   -------------
and construed in accordance with, the laws of the State of New York applicable
to contracts executed in and to be performed in that State.


                                        4


               IN WITNESS WHEREOF, each of the Purchaser and the Company has
caused this Amendment to be executed as of the date first written above by their
respective officers thereunto duly authorized.


                                          REN CORPORATION-USA

                                          By
                                            ------------------------
                                            Name:
                                            Title:



                                          COBE LABORATORIES, INC.



                                          By
                                            ------------------------
                                             Name:
                                             Title:





                                                             EXHIBIT B
                                                             ---------


                             CONTENTS OF OPINION OF
                     WYATT, TARRANT, COMBS, GIBERT & MILAN

1. The Company is a corporation duly organized, validly existing and in good
standing under the laws of Tennessee and has the requisite corporate power and
authority to own, lease and operate its properties and carry on its business in
all material respects as presently owned or conducted. The Company is duly
qualified or licensed as a foreign corporation to do business, and is in good
standing, in each jurisdiction where the character of its properties owned,
leased or operated by it, or the nature of its activities makes such
qualification or licensing necessary, except those jurisdictions, if any, in
which the failure to be so duly qualified or licensed and in good standing would
not, taken as a whole, have a Material Adverse Effect.

2. The Company is not in violation of any of the provisions of the Charter of
Incorporation or By-Laws, except where such violation would not, individually or
in the aggregate, have a Material Adverse Effect.

3. The Company has all necessary corporate power and authority to execute and
deliver the Agreement and to perform its obligations and to consummate the
transactions contemplated thereunder. The execution, delivery and performance of
the Agreement by the Company have been duly and validly authorized by all
necessary corporate action and no other corporate proceedings on the part of the
Company are necessary to authorize the Agreement or to consummate the
transactions contemplated thereunder.

4. (a) The execution and delivery of the Agreement by the Company do not, and
the performance of the Agreement (including, without limitation, the
consummation of the transactions contemplated thereunder) will not, (i) conflict
with or violate the Charter of Incorporation or By-Laws, (ii) conflict with or
violate any law, rule, regulation, order, judgment or decree applicable to the
Company, or by which its or any of its properties are bound or affected, or
(iii) result in any breach of or constitute a default (or an



                                        2

event which with notice or lapse of time or both would become a default) under,
or give to others any rights of termination, amendment, acceleration or
cancellation of, or result in the creation of a lien or encumbrance on any of
the properties or assets of the Company which would have a Material Adverse
Effect, taken as a whole, pursuant to any note, bond, mortgage, indenture,
contract, agreement, lease, license, permit, insurance policy or other
instrument or obligation, and which note, bond, mortgage, indenture, contract,
agreement, license, permit, insurance policy or other instrument or obligation
to which the Company is a party, or by which the Company or its properties are
bound or affected.

(b)  The execution and delivery of the Agreement by the Company do not, and the
performance of the Agreement by the Company (including, without limitation, the
consummation of the transactions thereunder) will not require any consent,
approval, authorization or permit of, or filing (other than filings, if any,
required on Form 8-K with the SEC and the HSR Act) with or notification to, any
governmental or regulatory authority, domestic or foreign, on the part of the
Company.

5.   Following the consummation of the transactions thereunder, all the Shares
subject to issuance pursuant to the Agreement, upon such issuance against
payment for such Shares as contemplated by the Agreement shall (i) be duly
authorized, validly issued, fully paid and nonassessable, (ii) not be subject to
any Encumbrances and (iii) such Shares shall have accorded to them voting
rights.

6.   The Agreement has been duly and validly executed and delivered by the
Company and, assuming the due authorization, execution and delivery hereof by
the Purchaser, and payment for the Shares as contemplated by the Agreement,
constitutes the legal, valid and binding obligation of the Company enforceable
against the Company in accordance with its terms, except as such enforceability
may be limited by bankruptcy, insolvency, reorganization or other similar laws
affecting creditors' rights generally and by the availability of equitable
remedies.

     The following assumptions shall be made:

1.   Reliance upon representations and warranties of the Company and upon
     certificates of certain public officials;



                                       3

2.   Authenticity of all documents submitted to us as copies, genuineness of all
     signatures, and conformity to the originals of all documents submitted to
     counsel as copies;

3.   Due authorization, execution and delivery of the Agreement by the
     Purchaser;

4.   Neither the Purchaser nor any Affiliate of the Purchaser has acquired any
     shares of Voting Securities other than the Shares during the 90 day period
     prior to the Closing, and neither the Purchaser nor any Affiliate of the
     Purchaser will acquire any shares of Voting Securities other than the
     Shares during a period of 90 days after the Closing; and

5.   Compliance by the Company, the Purchaser and any Affiliate of either the
     Company or the Purchaser with the covenants, representations, warranties
     and agreements made, and to be performed by them pursuant to the Agreement.








                                                    EXECUTION COPY

                         AMENDMENT NO. 1 TO THE
               FEBRUARY 9, 1992 STOCK PURCHASE AGREEMENT

               AMENDMENT NO. 1, dated as of March 17, 1992 (this "Amendment") to
                                                                  ---------
the Stock Purchase Agreement, dated as of February 9, 1992 between REN 
CORPORATION-USA, a Tennessee corporation (the "Company"), and COBE LABORATORIES,
                                               -------
INC., a Colorado corporation (the "Purchaser").
                                   ---------


                               W I T N E S S E T H
                               - - - - - - - - - -

               WHEREAS, the Company and the Purchaser have entered into as of 
February 9, 1992 a Stock Purchase Agreement (the "1992 Purchase Agreement"; 
                                                  -----------------------
capitalized terms used and not defined herein being used herein as defined in 
the 1992 Purchase Agreement); and

               WHEREAS, the Company and the Purchaser have determined that it 
is in their mutual interests to amend the 1992 Purchase Agreement as hereinafter
set forth.

               NOW THEREFORE, in consideration of the premises and of the mutual
agreements and understandings hereinafter set forth, the Purchaser and the 
Company agree as follows:

               SECTION 1. Amendments to the 1992 Purchase Agreement. The 1992 
                          -----------------------------------------
Purchase Agreement is, effective as of the date hereof, hereby amended as 
follows:

               (a) Section 3.03(a) shall be restated in full to
     read as follows:

               "(a) The authorized capital stock of the Company consists 
               of (x) 10,000,000 shares of Preferred Stock, of which none 
               is issued, outstanding or reserved for issuance, and (y) 
               60,000,000 shares of Common Stock, of which (i) 11,722,575 
               shares of Common Stock are issued and outstanding, (ii)
               0 shares of Common Stock are held in the treasury of the 
               Company, (iii) an aggregate of 271,400 shares of Common Stock 
               are subject to outstanding options, and 481,125 shares are 
               reserved for issuance, pursuant to the Company's Stock 
               Option Plan, (iv) an aggregate of 331,838 shares of Common 
               Stock are subject to outstanding promissory notes that are 
               convertible into shares of Common Stock, and (v) an aggregate 
               of 100,700 shares of Common Stock are subject to outstanding 
               warrants that are exercisable into shares of Common Stock. Of 
               the 11,722,575 shares of Common Stock that are issued and






               outstanding, 180,000 shares are held in escrow on behalf of the
               Company and certain shareholders, in connection with a settlement
               of a claim arising from an acquisition of a treatment center in 
               Douglas, Georgia."

               (b) The second sentence of Section 5.02 shall be restated in full
     to read as follows:

               "Each party hereto agrees to make, or cause its 'ultimate parent 
               entity' (as such term is defined in the HSR Act) to make, an 
               appropriate filing of a Notification and Report Form pursuant 
               to the HSR Act as soon as reasonably practicable after the date 
               hereof."

               SECTION 2. Counterparts. This Amendment may be executed in one 
                          ------------
or more counterparts, and by the different parties hereto in separate 
counterparts, each of which when executed shall be deemed to be an original, 
but all of which taken together shall constitute one and the same agreement.

               SECTION 3. Governing Law. This Amendment shall be governed by, 
                          -------------
and construed in accordance with, the laws of the State of New York applicable 
to contracts executed in and to be performed in that State.

               IN WITNESS WHEREOF, each of the Purchaser and the Company has 
caused this Amendment to be executed as of the date first written above by their
respective officers thereunto duly authorized.

                                          REN CORPORATION-USA

                                          By /s/ Jerome S. Tannebaum
                                            ------------------------------
                                            Name: Jerome S. Tannebaum
                                            Title: Chief Executive Officer





                                          COBE LABORATORIES INC.


                                          BY /s/ Ronald F. Plusk
                                             --------------------------
                                             Name:  Ronald F. Plusk
                                             Title: Vice President
                                                    and Chief Financial
                                                    Officer