<PAGE>   1
                                                                  EXHIBIT 10.9

                                 TENET BUYPOWER
                         PURCHASING ASSISTANCE AGREEMENT

This Purchasing Assistance Agreement (this "Agreement") is entered into by and
between Iasis Healthcare Corporation, a Delaware corporation as successor in
interest to JLL Hospital, LLC, a Delaware limited liability company, for itself
and on behalf of its subsidiaries identified on Exhibit A, attached hereto and
incorporated herein by this reference (collectively hereinafter, "Purchaser"),
located at 104 Woodmont, Suite 101, Nashville, Tennessee 37205, and Tenet
HealthSystem Medical, Inc., on behalf of itself and its affiliates, a Delaware
Corporation ("Tenet"), located at 14001 Dallas Parkway, Dallas, Texas 75240.

                                   WITNESSETH:

A.       Purchaser (through its direct and indirect subsidiaries) owns and/or
         operates those certain facilities listed on Exhibit B, attached hereto
         and incorporated herein by this reference (hereinafter referred to as
         "a facility" or collectively as "the facilities"), through which
         Purchaser and its direct and indirect subsidiaries (collectively,
         "Hospital") provides medical and hospital services.

B.       Tenet maintains agreements for purchasing various goods, supplies,
         materials, dietary products, pharmaceutical and equipment used by
         hospitals on a national basis.

C.       Hospital desires to purchase such goods, supplies, materials, dietary
         products, pharmaceutical and equipment under said national supply and
         purchase agreements to the extent permitted by such agreements, and to
         the extent that the price for purchase hereunder would be based upon
         meeting vendor terms and conditions.

NOW, THEREFORE, in consideration of the mutual covenants and agreements set
forth, it is agreed as follows:

1.       PURPOSE:

         Hospital hereby employs Tenet to assist Hospital in the purchasing of
         various supplies, goods, materials, dietary products, pharmaceutical
         and equipment used in the Hospital's normal and customary operations of
         the facilities and Tenet agrees to assist Hospital in the purchasing of
         such supplies, goods, materials, dietary products, pharmaceutical and
         equipment for the facilities, all as is more fully set forth below.

2.       TERM:

         Subject to prior termination under Paragraph 6, below, the term of this
         Agreement shall be for a period of one year commencing on October 5,
         1999, and ending on October 16, 2000 (the "Initial Term"); provided,
         however, that unless notice of termination is provided by Hospital at
         least 30 days prior to the expiration of the Initial Term or any
         renewal term, this agreement shall automatically be extended for
         successive one year periods.


<PAGE>   2

3.       TENET'S RESPONSIBILITIES:

         a.       Prior to the commencement date of this Agreement, Tenet has
                  delivered, or caused to be delivered, to Hospital a copy (or
                  brief summary hereof) of all national purchase and supply
                  agreements which Tenet has in effect at that time.
                  Additionally, Tenet will, during the term hereof, provide
                  Hospital with copies of any additional amendments, changes, or
                  terminations to such agreements on a timely basis so that
                  Hospital can be advised thereof.

         b.       Tenet will provide consultation with Hospital to effect a
                  smooth transition.

         c.       Tenet shall notify each of the contracting parties to such
                  national purchase and supply agreements that Hospital is
                  participating in such agreements to the extent permitted by
                  such agreements and accordingly is entitled to purchase of
                  such goods, supplies, materials, dietary products,
                  pharmaceutical and equipment and receive the same discounts
                  thereunder as Tenet.

         d.       Hospital acknowledges that Tenet has certain subsidiaries and
                  divisions in the health care field. Certain of these
                  subsidiaries or divisions may, from time to time, make
                  proposals to or do business with Hospital. Tenet shall in each
                  instance cause the disclosure of the related nature of such
                  enterprises, and Hospital shall in each such instance be free
                  to enter into or reject any such proposals or business dealing
                  solely on the respective merits.

4.       REPRESENTATIONS AND COVENANTS OF HOSPITAL:

         Hospital hereby represents to and covenants with Tenet as follows:

         a.       All purchasing by Hospital of goods, supplies, materials,
                  dietary products, pharmaceuticals and equipment under said
                  national purchasing and supply agreements shall be in the name
                  of Hospital or its controlled affiliates, and Hospital shall
                  be solely responsible for payment therefor.

         b.       Any purchase by Hospital under any such national purchase and
                  supply agreement will be between Hospital and the respective
                  contractor; Tenet does not make any warranty, express or
                  implied, as to such goods, supplies, materials, dietary
                  products, pharmaceuticals or equipment.

         c.       Hospital shall indemnify and hold Tenet harmless from any
                  liability brought against them or any of them as a result of
                  Hospital's action or inaction with respect to such national
                  purchase and supply agreements.

5.       ADMINISTRATIVE FEES:

         Tenet shall share back 50% of all administrative fees paid by suppliers
         against the Hospital's purchases as identified in Paragraph 8 of this
         Agreement.

6.       TERMINATION:

         a.       During the term hereof, either party may terminate this
                  Agreement with or without



<PAGE>   3


                  cause at any time by giving written notice to the other, such
                  termination to be effective sixty (60) days after the date
                  such notice is given.

         b.       Upon termination of this Agreement, whether by expiration of
                  its term or otherwise, provided that Tenet is not performing
                  services on a month-to-month basis as provided in Paragraph 2
                  above, neither Hospital nor Tenet shall have any further
                  obligations hereunder, and particularly no obligation to
                  maintain, update, or advise concerning any system or procedure
                  provided hereunder.

7.       SUCCESSORS AND ASSIGNS:

         a.       No party hereto may assign its interest in or delegate the
                  performance of its obligations under this Agreement to any
                  other person without obtaining the prior written consent of
                  the other party. Hospital may assign its interest to a duly
                  authorized successor in interest provided, however, that any
                  such transferee or assignee shall expressly assume in writing
                  the obligations of Hospital to Tenet as set forth herein.

         b.       The terms, provisions, covenants, obligations and conditions
                  of this Agreement shall be binding upon and shall inure to the
                  benefit of the successors in interest and the assigns of the
                  parties hereto, provided that no assignment, transfer, pledge
                  or mortgage by or through either party, as the case may be, in
                  violation of the provisions of this Agreement, shall vest any
                  rights in the assignee, transferee, pledgee or mortgagee.

8.       FEE FOR PURCHASING ASSISTANCE AGREEMENT:

         Hospital acknowledges that, as part of an agreement to furnish goods or
         services to Hospital, Tenet may receive a group purchasing
         administrative fee in connection with certain products that are
         purchased, licensed or leased by Hospital. Such payment shall equal 3%
         or less of the purchase price of the goods or services provided by the
         participating vendor. Tenet shall disclose to Hospital in writing, on
         an annual basis, and to the Secretary of Health and Human Services upon
         his or her request, the amount received from each vendor with respect
         to purchases made by or on behalf of Hospital. Within 90 days after the
         end of each fiscal quarter of Tenet (FYE May 31) during the term of
         this Agreement, Tenet shall provide Hospital with information from
         venders regarding administrative fees with respect to purchases by
         Hospital hereunder for such quarterly period.

9.       NOTICES:

         Any notice by any party to the other shall be in writing and shall be
         deemed to have been given on the earlier of (a) the date on which it is
         delivered personally or (b) four (4) days after it is deposited in the
         U.S. mail, postage prepaid, certified with return receipt requested and
         addressed to the party at its address as set forth on Page 1 of this
         Agreement (or at such other address as may have been designated by the
         party pursuant to this Paragraph 9).


<PAGE>   4

10.      APPLICABLE LAW:

         This Agreement is entered into in the State of New York and shall be
         governed by the laws of the State of York and all actions concerning
         this Agreement shall be brought in the courts of the State of New York.

11.      ACCESS TO BOOKS AND RECORDS OF TENET BY SECRETARY OF HHS OR AUTHORIZED
         REPRESENTATIVE:

         Upon written request of the Secretary of Health and Human Services or
         the Comptroller General or any of their duly authorized
         representatives, Tenet or any other related organization providing
         services with a value or cost of ten thousand dollars ($10,000.00) or
         more, over a twelve (12) month period, shall make available to the
         Secretary the contracts, books, documents and records that are
         necessary to certify the nature and extent of the costs of providing
         such services. Such inspection shall be available up to four (4) years
         after the rendering of such services. This paragraph is not intended to
         prohibit or impede any state audits pursuant to state law.

12.      ENTIRE AGREEMENT:

         This Agreement constitutes the sole and only Agreement of the parties
         hereto with respect to purchasing assistance services to the facilities
         and correctly sets forth the rights, duties, and obligations of each to
         the other as of its date. Any and all prior agreements, promises,
         proposals, negotiations or representations, whether written or oral
         with respect to purchasing assistance services to the facilities, which
         are not expressly set forth in this Agreement are hereby superseded and
         are of no force or effect. This Agreement is considered confidential,
         therefore, any specifics of this Agreement will not be discussed unless
         mutual consent has been agreed upon by both parties.


<PAGE>   5



IN WITNESS WHEREOF, the parties have caused this instrument to be duly executed

by their authorized representatives this 15th day of October, 1999.

TENET HEALTHSYSTEM MEDICAL, INC.            IASIS HEALTHCARE CORPORATION

By: /s/ Paul O'Neill                                 /s/ Frank Coyle
   -------------------------                         ---------------------------
Name:  Paul O'Neill                                  Signature
Title: Vice President
                                                        Frank Coyle
                                                     ---------------------------
                                                     Print Name
                                                        Secretary
                                                     ---------------------------
                                                     Title



<PAGE>   6


                                    EXHIBIT A

                             PURCHASER SUBSIDIARIES



St. Luke's Medical Center, LP
St. Luke's Behavioral Center, LP
Health Choice Arizona, Inc.
Metro Ambulatory Surgery Center, Inc.
Biltmore Surgery Center, Inc.
Palms of Pasadena, LP
Odessa Regional Hospital, LP
Tempe St. Luke's Hospital, LP
Memorial Hospital of Tampa, LP
Mesa General Hospital, LP
Town & Country Hospital, LP
Southwest General Hospital, LP
SSJ St. Petersburg Holdings, Inc.
First Choice Physicians Network Holdings, Inc.
Baptist Joint Venture Holdings, Inc.
Beaumont Hospital Holdings, Inc.
Iasis Healthcare Holdings, Inc.


<PAGE>   7


                                   EXHIBIT B

                                   FACILITIES

HealthChoice Arizona
Memorial Hospital of Tampa
Mesa General Hospital
Mid-Jefferson Hospital
Odessa Regional Hospital
Palms of Pasadena Hospital
Park Place Medical Center
St. Luke's Medical Center
St. Luke's Behavioral Health Center
Southwest General Hospital
Tempe St. Luke's Hospital
Town & Country Hospital
Davis Hospital and Medical Center
Jordan Valley Hospital
Pioneer Valley Hospital
State Street Hospital
Salt Lake Regional Medical Center