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                                                                Exhibit 10.5


                            STOCK PURCHASE AGREEMENT

         This Stock Purchase Agreement (this "AGREEMENT") is made as of June 27,
2000 by and between Mitchell E. Hersh, an individual ("PURCHASER"), and Ampulla,
LLC, a Texas limited liability company (the "SELLER").

         WHEREAS, the Seller owns all of the outstanding voting capital stock
(the "SHARES") of Prentiss Properties Limited, Inc., a Delaware corporation (the
"COMPANY").

         WHEREAS, the Seller desires to sell to Purchaser, and the Purchaser
desires to purchase from the Seller, all of the Shares on the terms and subject
to the conditions contained herein.

         WHEREAS, the execution of this Agreement is a condition to and an
inducement for Mack-Cali Realty Corporation and Mack-Cali Realty, L.P. to enter
into that certain Agreement and Plan of Merger, dated as of the date hereof, by
and among Mack-Cali Realty Corporation, Mack-Cali Realty, L.P., Prentiss
Properties Trust and Prentiss Properties Acquisition Partners, L.P. (the "MERGER
AGREEMENT").

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

         1. SALE AND PURCHASE OF THE SHARES. At the Closing (as hereinafter
defined) and upon the terms and subject to the conditions of this Agreement, the
Seller shall sell, deliver and transfer to the Purchaser, and the Purchaser
shall purchase and acquire from the Seller, all right, title and interest in and
to the Shares. As consideration for the purchase of the Shares, Purchaser shall
pay to the Seller the sum of One Hundred and Twenty Five Thousand Dollars
($125,000) (the "PURCHASE PRICE"). The Purchase Price shall be paid at Closing
by wire transfer of immediately available funds.

         2. CLOSING DELIVERIES. Subject to the conditions contained in this
Agreement, the deliveries contemplated by SECTION 1 hereof shall occur at such
time and date as the Merger (as defined in the Merger Agreement) is effected
(the "CLOSING"). To effect the transfer of the Shares, at the Closing (a) the
Seller will deliver to the Purchaser all original stock certificates evidencing
the Shares, duly endorsed or accompanied by appropriate stock powers, and (b)
the Purchaser will deliver to the Seller the Purchase Price in the manner
contemplated in SECTION 1 hereof. The deliveries set forth above shall be
considered to have taken place simultaneously, and no delivery shall be deemed
to have been completed until all other deliveries have been completed.

         3. REPRESENTATIONS AND WARRANTIES OF THE SELLER. The Seller represents
and warrants to the Purchaser as follows:

            3.1. OWNERSHIP. The Seller is the record and beneficial owner of the
Shares, free and clear of all liens, security interests, pledges, claims,
liabilities and restrictions of any nature whatsoever.

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            3.2. TITLE TO SHARES. The Purchaser shall acquire good and
marketable title to such Shares being purchased by such Purchaser from the
Seller free and clear of any liens, security interests, encumbrances and
restrictions of any nature whatsoever, except for restrictions imposed by
applicable federal and state securities laws.

            3.3. ORGANIZATION AND AUTHORITY. The Seller is a limited
liability company duly organized, validly existing and in good standing under
the laws of the State of Texas and has all requisite limited liability company
power and authority to enter into and perform this Agreement and to carry out
the transactions contemplated by this Agreement. The execution, delivery and
performance by the Seller of this Agreement and the consummation of the
transactions contemplated hereby by the Seller have been duly authorized by all
necessary company action on the part of the Seller. This Agreement has been duly
executed and delivered by the Seller and is a valid and binding obligation of
the Seller enforceable against the Seller in accordance with its terms, except
as such enforceability may be limited by bankruptcy, insolvency, reorganization,
moratorium and similar laws relating to or affecting creditors' rights generally
and by general equitable principles (regardless of whether such enforceability
is considered in a proceeding in law or in equity).

            3.4. NO CONFLICTS. The execution, delivery and performance of
this Agreement and the consummation of the transactions contemplated by this
Agreement do not and will not conflict with or result in any breach of any
terms, conditions or provisions of, or constitute a default, under (a) the
Seller's Articles of Organization or by-laws (each as amended to date and
presently in effect), (b) any agreement or other instrument to which the Seller
is a party or by which it or any of its properties is bound and which conflict,
breach or default would have a material adverse effect upon the Seller, its
assets, properties, business or condition (financial or otherwise) or (c) any
decree, judgment, order, statute, rule or regulation applicable to the Seller.

            3.5. NO CONSENTS. No consent, approval, order, authorization
or waiver from, notice to or declaration, registration or filing with any
governmental authority or any other person is necessary in connection with the
execution, delivery and performance by the Seller of this Agreement or the
consummation of the transactions contemplated hereby.

         4. REPRESENTATIONS AND WARRANTIES OF THE PURCHASER. The Purchaser
represents and warrants to the Seller as follows:

            4.1. ORGANIZATION AND AUTHORITY. This Agreement has been duly
executed and delivered by the Purchaser and is a valid and binding obligation of
the Purchaser enforceable against the Purchaser in accordance with its terms,
except as such enforceability may be limited by bankruptcy, insolvency,
reorganization, moratorium and similar laws relating to or affecting creditors'
rights generally and by general equitable principles (regardless of whether such
enforceability is considered in a proceeding in law or in equity).

            4.2. NO CONFLICTS. The execution, delivery and performance of
this Agreement and the consummation of the transactions contemplated by this
Agreement do not and will not conflict with or result in any breach of any of
the terms, conditions or provisions of, or constitute


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a default under (a) any agreement or other instrument to which the Purchaser is
party or by which it or any of its properties is bound and which conflict,
breach or default would have a material adverse effect upon the Purchaser, its
assets, properties, business or condition (financial or otherwise) or (b) any
decree, judgment, order, statute, rule or regulation applicable to the
Purchaser.

            4.3. NO CONSENTS. No consent, approval, order, authorization
or waiver from, notice to or declaration, registration or filing with any
governmental authority or any other person is necessary in connection with the
execution, delivery and performance by the Purchaser of this Agreement or the
consummation of the transactions contemplated hereby.

            4.4. ACCESS TO INFORMATION. The Purchaser has received or has
had full access to all the information it considers necessary or appropriate to
make an informed decision with respect to the Shares to be purchased by such
Purchaser under this Agreement. The Purchaser has had an opportunity to ask
questions and receive answers from the Company and the Seller regarding the
terms and conditions of the purchase of the Shares and to obtain additional
information (to the extent the Company or the Seller possessed such information
or could acquire it without unreasonable effort or expense) necessary to verify
any information furnished to such Purchaser or to which such Purchaser has had
access.

            4.5. INVESTMENT REPRESENTATIONS. The Purchaser understands
that the Shares have not been registered under the Securities Act of 1933, as
amended. The Purchaser is acquiring the Shares for investment purposes only and
is not purchasing the Shares with a view to the sale or distribution of any part
thereof. The Purchaser has made such investigation into the Company that
Purchaser considers necessary and appropriate to its purchase of the Shares, is
capable of evaluating the merits and risks of its purchase of the Shares, and is
relying solely upon such investigation and not upon any representation or
warranty made by Seller or the Company, other than the representations and
warranties specifically made in this Agreement.

         5. TERMINATION. This Agreement shall be terminated upon the occurrence
of any of the following circumstances:

         (a) By mutual written agreement of the Seller and the Purchaser; or

         (b) Upon the termination of the Merger Agreement in accordance with its
terms.

         6.  MISCELLANEOUS.

             6.1. NOTICES. All notices, consents and other communications
required or permitted under this Agreement shall be in writing, and shall be
deemed to have been duly given (a) when delivered personally, (b) when
received if sent by first class certified mail, postage prepaid, return
receipt requested, or (c) when delivered by an internationally recognized
overnight delivery service, postage or delivery charges prepaid, to a party.
Notices may also be given by facsimile and shall be effective on the date
transmitted if confirmed within twenty-four (24) hours thereafter by a signed
original sent in the manner provided in the preceding sentence. Any party may
change its address for notices by giving notice of a new address to the other
party in accordance with this SECTION 6.1, except that any such change of
address notice shall not be

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effective unless and until received. Any notice shall be sent to the parties
at the addresses set forth below:

                  If to the Seller:

                  Ampulla, L.L.C.
                  Michael V. Prentiss
                  5006 Seneca
                  Dallas, Texas 75209
                  Fax Number: (214) 351-5006

                  With a copy to:

                  Akin, Gump, Strauss, Hauer & Feld, L.L.P.
                  1700 Pacific Avenue, Suite 4100
                  Dallas, Texas 75201
                  Fax Number:  (214) 969-4343
                  Attn.:  Michael E. Dillard, P.C.

                  If to the Purchaser:

                  Mitchell E. Hersh
                  Mack-Cali Realty Corporation
                  11 Commerce Drive
                  Cranford, New Jersey  07016
                  Fax Number: (908) 272-6755

                  With a copy to:

                  Pryor, Cashman, Sherman & Flynn, LLP
                  410 Park Avenue
                  New York, New York  100222
                  Fax Number: (212) 326-0806
                  Attn.:  Blake Hornick, Esq.

             6.2. ENTIRE AGREEMENT. This Agreement constitutes the entire
agreement of the parties with respect to the subject matter hereof and
supersedes any and all prior written or oral communications and agreements, and
all contemporaneous oral communications among the parties concerning the subject
matter hereof.

             6.3. AMENDMENTS. No provision of this Agreement may be
amended, changed or modified in any manner, orally or otherwise, except by an
instrument in writing signed by the parties affected by such provision.

             6.4. SUCCESSORS AND ASSIGNS. This Agreement shall be binding
upon and inure to the benefit of the parties and their respective beneficiaries,
heirs, executors, administrators,


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successors and assigns. No party shall in any manner assign any of its rights or
obligations under this Agreement without the prior written consent of the other
party.

             6.5. GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS, WITHOUT GIVING
EFFECT TO PRINCIPLES OF CONFLICTS OF LAW OF ANY JURISDICTION.

             6.6. COUNTERPARTS. This Agreement may be executed in two or
more counterparts, each of which shall be deemed an original but all of which
together shall constitute one and the same instrument.

             6.7. SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All
representations and warranties contained herein shall survive the execution and
delivery of this Agreement and the Closing hereof, regardless of any
investigation at any time made by or on behalf of any party hereto.

             6.8. FURTHER ASSURANCES. At the Closing and thereafter, from
time to time and without additional consideration, the Seller and the Purchaser,
as the case may be, shall execute and deliver, or cause to be executed and
delivered, such additional or further transfers, assignments, endorsements,
consents and other instruments as the Purchaser or the Seller, as the case may
be, may reasonably request for the purpose of effectively carrying out the
transactions contemplated by this Agreement.


                            [SIGNATURE PAGE FOLLOWS]





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         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.

                                       SELLER:

                                       AMPULLA, L.L.C.

                                       By: /s/ Michael V. Prentiss
                                       -----------------------------
                                       Michael V. Prentiss
                                       Sole Member


                                       PURCHASER:

                                       /s/ Mitchell E. Hersh
                                       -----------------------------
                                       Mitchell E. Hersh







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