Exhibit (d)(4)

                      [Letterhead of UBS Securities Inc.]
 
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
                              REN CORPORATION-USA
                                       AT
                              $20.00 NET PER SHARE
                                       BY
                             REN ACQUISITION CORP.
                     AN INDIRECT WHOLLY OWNED SUBSIDIARY OF
                                   GAMBRO AB
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    THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
     CITY TIME, ON TUESDAY, OCTOBER 17, 1995 UNLESS THE OFFER IS EXTENDED.
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                                                              September 19, 1995
 
To Brokers, Dealers, Commercial Banks,
  Trust Companies and Other Nominees:
 
    We have been appointed by REN Acquisition Corp., a Tennessee corporation
("Purchaser") and an indirect wholly owned subsidiary of Gambro AB ("Gambro"), a
Swedish corporation, to act as Dealer Manager in connection with Purchaser's
offer to purchase all outstanding shares of common stock, no par value (the
"Shares"), of REN Corporation-USA, a Tennessee corporation (the "Company"), at a
price of $20.00 per Share, net to the seller in cash, upon the terms and subject
to the conditions set forth in Purchaser's Offer to Purchase, dated September
19, 1995 (the "Offer to Purchase"), and the related Letter of Transmittal (which
together constitute the "Offer") enclosed herewith. Please furnish copies of the
enclosed materials to those of your clients for whose accounts you hold Shares
registered in your name or in the name of your nominee.
 
    THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY AND
NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER AT LEAST A MAJORITY OF THE
THEN OUTSTANDING SHARES, OTHER THAN SHARES OWNED BENEFICIALLY BY OR OF RECORD BY
GAMBRO OR ANY OF ITS AFFILIATES. THE OFFER IS SUBJECT TO OTHER CERTAIN
CONDITIONS SET FORTH IN THE OFFER TO PURCHASE.
 
    Enclosed for your information and use are copies of the following documents:
 
    1. Offer to Purchase, dated September 19, 1995;
 
    2. Letter of Transmittal to be used by holders of Shares in accepting the
Offer and tendering Shares;
 
    3. Notice of Guaranteed Delivery to be used to accept the Offer if the
Shares and all other required documents are not immediately available or cannot
be delivered to The Bank of New York (the "Depositary") by the Expiration Date
(as defined in the Offer to Purchase) or if the procedure for book-entry
transfer cannot be completed by the Expiration Date;

    4. A letter to stockholders of the Company from Lawrence J. Centella,
President and Chief Executive Officer of the Company, together with a
Solicitation/Recommendation Statement on Schedule 14D-9 filed with the
Securities and Exchange Commission by the Company;
 
    5. A letter which may be sent to your clients for whose accounts you hold
Shares registered in your name or in the name of your nominee, with space
provided for obtaining such clients' instructions with regard to the Offer;
 
    6. Guidelines for Certification of Taxpayer Identification Number on
Substitute Form W-9; and
 
    7. Return envelope addressed to the Depositary.
 
    WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE. PLEASE NOTE
THAT THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
TIME, ON TUESDAY, OCTOBER 17, 1995, UNLESS THE OFFER IS EXTENDED.
 
    In all cases, payment for Shares accepted for payment pursuant to the Offer
will be made only after timely receipt by the Depositary of certificates
evidencing such Shares (or a confirmation of a book-entry transfer of such
Shares into the Depositary's account at one of the Book-Entry Transfer
Facilities (as defined in the Offer to Purchase)), a Letter of Transmittal (or
facsimile thereof) properly completed and duly executed and any other required
documents.
 
    If holders of Shares wish to tender, but cannot deliver such holder's
certificates, or cannot comply with the procedure for book-entry transfer, prior
to the expiration of the Offer, a tender of Shares may be effected by following
the guaranteed delivery procedure described under "THE TENDER OFFER -- Section
3. Procedures for Accepting the Offer and Tendering Shares" in the Offer to
Purchase.
 
    Purchaser will not pay any fees or commissions to any broker, dealer or
other person (other than the Dealer Manager, the Depositary and the Information
Agent as described in the Offer) in connection with the solicitation of tenders
of Shares pursuant to the Offer. However, Purchaser will reimburse you for
customary mailing and handling expenses incurred by you in forwarding any of the
enclosed materials to your clients. Purchaser will pay or cause to be paid any
stock transfer taxes payable with respect to the transfer of Shares to it,
except as otherwise provided in Instruction 6 of the Letter of Transmittal.
 
    Any inquiries you may have with respect to the Offer should be addressed to
UBS Securities Inc. (in such capacity, the "Dealer Manager") or Georgeson &
Company Inc. (the "Information Agent") at their respective addresses and
telephone numbers set forth on the back cover page of the Offer to Purchase.
 
    Additional copies of the enclosed material may be obtained from the
Information Agent, at the addresses and telephone numbers set forth on the back
cover page of the Offer to Purchase.
 
                                          Very truly yours,




                                          UBS SECURITIES INC.
 
    NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY OTHER PERSON THE AGENT OF GAMBRO, PURCHASER, COBE, THE COMPANY, THE
DEALER MANAGER, THE INFORMATION AGENT OR THE DEPOSITARY, OR OF ANY AFFILIATE OF
ANY OF THEM, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR TO MAKE
ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN
THE ENCLOSED DOCUMENTS AND THE STATEMENTS CONTAINED THEREIN.
 
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