<PAGE>

                                                                     Exhibit 4.2


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                             MACK-CALI REALTY, L.P.,

                                     ISSUER

                                       to

                            WILMINGTON TRUST COMPANY,

                                     TRUSTEE


                            -------------------------


                          Supplemental Indenture No. 3

                          Dated as of December 21, 2000

                            -------------------------



                                   $15,000,000
                                       of
                              7.835% Notes due 2010


--------------------------------------------------------------------------------

<PAGE>

            SUPPLEMENTAL INDENTURE NO. 3, dated as of December 21, 2000 (the
"SUPPLEMENTAL INDENTURE"), between MACK-CALI REALTY, L.P., a limited partnership
duly organized and existing under the laws of the State of Delaware (herein
called the "ISSUER"), and WILMINGTON TRUST COMPANY, a Delaware banking
corporation duly organized and existing under the laws of the State of Delaware,
as Trustee (herein called the "TRUSTEE").

                             RECITALS OF THE ISSUER

            The Issuer and Mack-Cali Realty Corporation, a corporation duly
organized and existing under the laws of the State of Maryland (herein called
the "CORPORATION"), have heretofore delivered to the Trustee an Indenture dated
as of March 16, 1999 (the "ORIGINAL Indenture"), a form of which has been filed
with the Securities and Exchange Commission under the Securities Act of 1933, as
amended, as an exhibit to the Issuer's Registration Statement on Form S-3
(Registration No. 333-57103), providing for the issuance from time to time of
Debt Securities of the Issuer (the "SECURITIES").

            Section 301 of the Original Indenture provides for various matters
with respect to any series of Securities issued under the Original Indenture to
be established in an indenture supplemental to the Original Indenture.

            Section 901(7) of the Original Indenture provides for the Issuer and
the Trustee to enter into an indenture supplemental to the Original Indenture to
establish the form or terms of Securities of any series as provided by Sections
201 and 301 of the Original Indenture.

            The Board of Directors of the Corporation, the general partner of
the Issuer, has duly adopted resolutions authorizing the Issuer to execute and
deliver this Supplemental Indenture.

            All the conditions and requirements necessary to make this
Supplemental Indenture, when duly executed and delivered, a valid and binding
agreement in accordance with its terms and for the purposes herein expressed,
have been performed and fulfilled.

        NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

            For and in consideration of the premises and the purchase of the
Securities provided for herein by the Holders thereof, it is mutually covenanted
and agreed, for the equal and proportionate benefit of all Holders of the Notes,
as follows:

<PAGE>

                                   ARTICLE ONE


                   RELATION TO ORIGINAL INDENTURE; DEFINITIONS

            Section 1.1  RELATION TO ORIGINAL INDENTURE.

            This Supplemental Indenture constitutes an integral part of the
Original Indenture.

            Section 1.2  DEFINITIONS.

            For all purposes of this Supplemental Indenture, except as otherwise
expressly provided for or unless the context otherwise requires:

            (1) Capitalized terms used but not defined herein shall have the
      respective meanings assigned to them in the Original Indenture; and

            (2) All references herein to Articles and Sections, unless otherwise
      specified, refer to the corresponding Articles and Sections of this
      Supplemental Indenture.

            "ACQUIRED INDEBTEDNESS" means Indebtedness of a Person (i) existing
at the time such Person becomes a Subsidiary or (ii) assumed in connection with
the acquisition of assets from such Person, in each case, other than
Indebtedness incurred in connection with, or in contemplation of, such Person
becoming a Subsidiary or such acquisition. Acquired Indebtedness shall be deemed
to be incurred on the date of the related acquisition of assets from any Person
or the date the acquired Person becomes a Subsidiary.

            "ANNUAL SERVICE CHARGE" for any period means the aggregate interest
expense for such period in respect of, and the amortization during such period
of any original issue discount of, Indebtedness of the Issuer and its
Subsidiaries.

            "BUSINESS DAY" means any day, other than a Saturday or Sunday, that
is neither a legal holiday nor a day on which banking institutions in the City
of New York or Delaware are authorized or required by law, regulation or
executive order to close.

            "CONSOLIDATED INCOME AVAILABLE FOR DEBT SERVICE" for any period
means Earnings from Operations of the Issuer and its Subsidiaries plus amounts
which have been deducted, and minus amounts which have been added, for the
following (without duplication): (i) interest on Indebtedness of the Issuer and
its Subsidiaries, (ii) provision for taxes of the Issuer and its Subsidiaries
based on income, (iii) amortization of debt discount and deferred financing
costs, (iv) provisions for gains and losses on properties and depreciation and
amortization, (v)

                                       2
<PAGE>

increases in deferred taxes and other non-cash items, (vi) depreciation and
amortization with respect to interests in joint venture and partially owned
entity investments, (vii) the effect of any charge resulting from a change in
accounting principles in determining Earnings from Operations for such period
and (viii) amortization of deferred charges.

            "CORPORATE TRUST OFFICE" means the office of the Trustee at which,
at any particular time, its corporate trust business shall be principally
administered, which office at the date hereof is located at Rodney Square North,
1100 North Market Street, Wilmington, Delaware 19890-0001, Attention: Corporate
Trust Administration and, for purposes of the Place of Payment provisions of
Sections 305 and 1002 of the Original Indenture, is located at Rodney Square
North, 1100 North Market Street, Wilmington, Delaware 19890-0001, Attention:
Corporate Trust Administration.

            "EARNINGS FROM OPERATIONS" for any period means net income excluding
provisions for gains and losses on sales of investments or joint ventures,
extraordinary and non-recurring items, and property valuation losses, as
reflected in the consolidated financial statements of the Issuer and its
Subsidiaries for such period determined in accordance with GAAP.

            "ENCUMBRANCE" means any mortgage, lien, charge, pledge or security
interest of any kind.

            "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended, and the rules and regulations promulgated thereunder by the Commission.

            "GAAP" means generally accepted accounting principles as used in the
United States applied on a consistent basis as in effect from time to time;
provided that solely for purposes of any calculation required by the financial
covenants contained herein, "GAAP" shall mean generally accepted accounting
principles as used in the United States on the date hereof, applied on a
consistent basis.

            "INDEBTEDNESS" of the Issuer or any Subsidiary means, without
duplication, any indebtedness of the Issuer or any Subsidiary, whether or not
contingent, in respect of: (i) borrowed money evidenced by bonds, notes,
debentures or similar instruments whether or not such indebtedness is secured by
any Encumbrance existing on property owned by the Issuer or any Subsidiary, (ii)
indebtedness for borrowed money of a Person other than the Issuer or a
Subsidiary which is secured by any Encumbrance existing on property owned by the
Issuer or any Subsidiary, to the extent of the lesser of (x) the amount of
indebtedness so secured and (y) the fair market value of the property subject to
such Encumbrance, (iii) the reimbursement obligations, contingent or otherwise,
in connection with any letters of credit actually issued or amounts representing
the balance deferred and unpaid of the purchase price of any property or
services, except any such balance that

                                       3
<PAGE>

constitutes an accrued expense or trade payable, or (iv) any lease of property
by the Issuer or any Subsidiary as lessee which is reflected on the Issuer's
consolidated balance sheet as a capitalized lease in accordance with GAAP; and
also includes, to the extent not otherwise included, any obligation by the
Issuer or any Subsidiary to be liable for, or to pay, as obligor, guarantor or
otherwise (other than for purposes of collection in the ordinary course of
business), Indebtedness of another Person (other than the Issuer or any
Subsidiary; it being understood that Indebtedness shall be deemed to be incurred
by the Issuer or any Subsidiary whenever the Issuer or such Subsidiary shall
create, assume, guarantee or otherwise become liable in respect thereof;
Indebtedness of a Subsidiary of the Issuer existing prior to the time it became
a Subsidiary of the Issuer shall be deemed to be incurred upon such Subsidiary's
becoming a Subsidiary of the Issuer; and Indebtedness of a person existing prior
to a merger or consolidation of such person with the Issuer or any Subsidiary of
the Issuer in which such person is the successor to the Issuer or such
Subsidiary shall be deemed to be incurred upon the consummation of such merger
or consolidation; provided, however, the term "Indebtedness" shall not include
any such indebtedness that has been the subject of an "in substance" defeasance
in accordance with GAAP).

            "INTERCOMPANY INDEBTEDNESS" means Indebtedness to which the only
parties are the Issuer, the Corporation and any Subsidiary (but only so long as
such Indebtedness is held solely by any of the Issuer, the Corporation and any
Subsidiary) that is subordinate in right of payment to the Notes.

            "MAKE-WHOLE PREMIUM" means, in connection with any optional
redemption of any Notes, the excess, if any, of (i) the aggregate present value
as of the date of such redemption of each dollar of principal of such Notes
being redeemed and the amount of interest (exclusive of interest accrued to the
date of redemption) that would have been payable in respect of such dollar if
such redemption had not been made, determined by discounting, on a semi-annual
basis, such principal and interest at the Reinvestment Rate (determined on the
third Business Day preceding the date such notice of redemption is given) from
the respective dates on which such principal and interest would have been
payable if such redemption had not been made, over (ii) the aggregate principal
amount of such Notes being redeemed.

            "NOTES" has the meaning specified in Section 2.1 hereof.

            "REINVESTMENT RATE" means 0.25% (twenty-five one hundredths of one
percent) plus the arithmetic mean of the yields under the respective headings
"This Week" and "Last Week" published in the Statistical Release under the
caption "Treasury Constant Maturities" for the maturity (rounded to the nearest
month) corresponding to the remaining life to maturity of such Notes, as of the
payment date of the principal of such Notes being redeemed. If no maturity
exactly corresponds to such maturity, yields for the two published maturities
most closely corresponding to such maturity shall be calculated pursuant to the
immediately preceding sentence and the Reinvestment Rate shall be obtained by
linear interpolation, rounding in each of

                                       4
<PAGE>

such relevant periods to the nearest month. For such purposes of calculating the
Reinvestment Rate, the most recent Statistical Release published prior to the
date of determination of the Make-Whole Premium shall be used.

            "STATISTICAL RELEASE" means the statistical release designated
"H.15(519)" or any successor publication which is published weekly by the
Federal Reserve System and which establishes yields on actively traded United
States government securities adjusted to constant maturities or, if such
statistical release is not published at the time of any determination of the
Make-Whole Premium, then such other reasonably comparable index which shall be
designated by the Issuer.

            "SUBSIDIARY" means, with respect to any Person, any corporation or
other entity of which a majority of the voting power of the voting equity
securities or the outstanding equity interests of which are owned, directly or
indirectly, by such Person. For the purposes of this definition, "voting equity
securities" means equity securities having voting power for the election of
directors, whether at all times or only so long as no senior class of security
has such voting power by reason of any contingency.

            "TOTAL ASSETS" as of any date means the sum of (i) the Undepreciated
Real Estate Assets and (ii) all other assets of the Issuer and its Subsidiaries
determined in accordance with GAAP (but excluding accounts receivable and
intangibles).

            "TOTAL UNENCUMBERED ASSETS" means the sum of (i) those Undepreciated
Real Estate Assets not subject to an Encumbrance for borrowed money and (ii) all
other assets of the Issuer and its Subsidiaries not subject to an Encumbrance
for borrowed money, determined in accordance with GAAP (but excluding accounts
receivable and intangibles).

            "UNDEPRECIATED REAL ESTATE ASSETS" as of any date means the cost
(original cost plus capital improvements) of real estate assets of the Issuer
and its Subsidiaries on such date, before depreciation and amortization,
determined on a consolidated basis in accordance with GAAP.

            "UNSECURED INDEBTEDNESS" means Indebtedness which is not secured by
any Encumbrance upon any of the properties of the Issuer or any Subsidiary.

                                       5
<PAGE>

                                   ARTICLE TWO

                               THE SERIES OF NOTES

            Section 2.1 TITLE OF THE SECURITIES.

            There shall be a series of Securities designated the "7.835% Notes
due 2010" (the "NOTES").

            Section 2.2  LIMITATION ON AGGREGATE PRINCIPAL AMOUNT.

            The aggregate principal amount of the Notes shall be limited to
$15,000,000, and, except as provided in this Section and in Section 306 of the
Original Indenture, the Issuer shall not execute and the Trustee shall not
authenticate or deliver Notes in excess of such aggregate principal amount.

            Nothing contained in this Section 2.2 or elsewhere in this
Supplemental Indenture, or in the Notes, is intended to or shall limit execution
by the Issuer or authentication or delivery by the Trustee of Notes under the
circumstances contemplated by Sections 303, 304, 305, 306, 906, 1107 and 1305 of
the Original Indenture.

            Section 2.3  INTEREST AND INTEREST RATES; MATURITY DATE OF NOTES.

            The Notes will bear interest at a rate of 7.835% per annum from
December 21, 2000 or from the immediately preceding Interest Payment Date to
which interest has been paid or duly provided for, payable semi-annually in
arrears on June 15 and December 15 of each year, commencing on June 15, 2001
(each, an "INTEREST PAYMENT DATE"), to the Person in whose name such Note is
registered at the close of business on June 1 or December 1 (whether or not a
Business Day), as the case may be, next preceding such Interest Payment Date
(each, a "REGULAR RECORD Date"). Interest will be computed on the basis of a
360-day year comprised of twelve 30-day months. The interest so payable on any
Note which is not punctually paid or duly provided for on any Interest Payment
Date shall forthwith cease to be payable to the Person in whose name such Note
is registered on the relevant Regular Record Date, and such defaulted interest
shall instead be payable to the Person in whose name such Note is registered on
the Special Record Date or other specified date determined in accordance with
the Original Indenture.

            If any Interest Payment Date or Maturity falls on a day that is not
a Business Day, the required payment shall be made on the next Business Day as
if it were made on the date such payment was due and no interest shall accrue on
the amount so payable for the period from and after such Interest Payment Date
or Maturity, as the case may be.

            The Notes will mature on December 15, 2010.

                                       6
<PAGE>

            Section 2.4  LIMITATIONS ON INCURRENCE OF INDEBTEDNESS.

            (a) The Issuer will not, and will not permit any Subsidiary to,
incur any Indebtedness, other than Intercompany Indebtedness, if, immediately
after giving effect to the incurrence of such additional Indebtedness and the
application of the proceeds thereof, the aggregate principal amount of all
outstanding Indebtedness of the Issuer and its Subsidiaries on a consolidated
basis determined in accordance with GAAP is greater than 60% of the sum of
(without duplication) (i) the Total Assets of the Issuer and its Subsidiaries as
of the end of the calendar quarter covered in the Issuer's Annual Report on Form
10-K or Quarterly Report on Form 10-Q, as the case may be, most recently filed
with the Commission (or, if such filing is not permitted under the Exchange Act,
with the Trustee) prior to the incurrence of such additional Indebtedness and
(ii) the purchase price of any assets included in the definition of Total Assets
acquired, and the amount of any securities offering proceeds received (to the
extent such proceeds were not used to acquire items included in the definition
of Total Assets or used to reduce indebtedness), by the Issuer or any Subsidiary
since the end of such calendar quarter, including those proceeds obtained in
connection with the incurrence of such additional Indebtedness.

            (b) In addition to the limitation set forth in subsection (a) of
this Section 2.4, the Issuer will not, and will not permit any Subsidiary to,
incur any Indebtedness if the ratio of Consolidated Income Available for Debt
Service to the Annual Service Charge for the four consecutive fiscal quarters
most recently ended prior to the date on which such additional Indebtedness is
to be incurred shall have been less than 1.5:1, on a PRO FORMA basis after
giving effect thereto and to the application of the proceeds therefrom, and
calculated on the assumption that (i) such Indebtedness and any other
Indebtedness incurred by the Issuer and its Subsidiaries since the first day of
such four-quarter period and the application of the proceeds therefrom,
including to refinance other Indebtedness, had occurred at the beginning of such
period; (ii) the repayment or retirement of any other Indebtedness by the Issuer
and its Subsidiaries since the first day of such four-quarter period had been
repaid or retired at the beginning of such period (except that, in making such
computation, the amount of Indebtedness under any revolving credit facility
shall be computed based upon the average daily balance of such Indebtedness
during such period); (iii) in the case of Acquired Indebtedness or Indebtedness
incurred in connection with any acquisition since the first day of such
four-quarter period, the related acquisition had occurred as of the first day of
such period with the appropriate adjustments with respect to such acquisition
being included in such PRO FORMA calculation; and (iv) in the case of any
acquisition or disposition by the Issuer or its Subsidiaries of any asset or
group of assets since the first day of such four-quarter period, whether by
merger, stock purchase or sale, or asset purchase or sale, such acquisition or
disposition or any related repayment of Indebtedness had occurred as of the
first day of such period with the appropriate adjustments with respect to such
acquisition or disposition being included in such PRO FORMA calculation.

                                       7
<PAGE>

            (c) In addition to the limitations set forth in subsections (a) and
(b) of this Section 2.4, the Issuer will not, and will not permit any Subsidiary
to, incur any Indebtedness secured by any Encumbrance upon any of the property
of the Issuer or any Subsidiary, whether owned at the date of the Indenture or
thereafter acquired, if, immediately after giving effect to the incurrence of
such additional Indebtedness secured by an Encumbrance and the application of
the proceeds thereof, the aggregate principal amount of all outstanding
Indebtedness of the Issuer and its Subsidiaries on a consolidated basis which is
secured by any Encumbrance on property of the Issuer or any Subsidiary is
greater than 40% of the sum of (without duplication) (i) the Total Assets of the
Issuer and its Subsidiaries as of the end of the calendar quarter covered in the
Issuer's Annual Report on Form 10-K or Quarterly Report on Form 10-Q, as the
case may be, most recently filed with the Commission (or, if such filing is not
permitted under the Exchange Act, with the Trustee) prior to the incurrence of
such additional Indebtedness and (ii) the purchase price of any assets included
in the definition of Total Assets acquired, and the amount of any securities
offering proceeds received (to the extent such proceeds were not used to acquire
items included in the definition of Total Assets or used to reduce
Indebtedness), by the Issuer or any Subsidiary since the end of such calendar
quarter, including those proceeds obtained in connection with the incurrence of
such additional Indebtedness.

            (d) The Issuer and its Subsidiaries may not at any time own Total
Unencumbered Assets equal to less than 150% of the aggregate outstanding
principal amount of the Unsecured Indebtedness of the Issuer and its
Subsidiaries on a consolidated basis.

            (e) For purposes of this Section 2.4, Indebtedness shall be deemed
to be "incurred" by the Issuer or a Subsidiary whenever the Issuer or such
Subsidiary shall create, assume, guarantee or otherwise become liable in respect
thereof.

            Section 2.5  REDEMPTION.

            The Notes may be redeemed at any time at the option of the Issuer,
in whole or in part, at a redemption price equal to the sum of (i) the principal
amount of the Notes being redeemed plus accrued and unpaid interest thereon up
to but not including the Redemption Date and (ii) the Make-Whole Premium, if
any, with respect to such Notes (the "REDEMPTION PRICE").

            Section 2.6  PLACES OF PAYMENT.

            The Places of Payment where the Notes may be presented or
surrendered for payment, where the Notes may be surrendered for registration of
transfer or exchange and where notices and demands to and upon the Issuer in
respect of the Notes and the Original Indenture may be served shall be in
Wilmington, Delaware,

                                       8
<PAGE>

and the office or agency for such purpose shall initially be located at the
Corporate Trust Office.

            Section 2.7  METHOD OF PAYMENT.

            Payment of the principal of and interest on the Notes will be made
at the office or agency of the Issuer maintained for that purpose in Wilmington,
Delaware (which shall initially be an office or agency of the Trustee), in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts; PROVIDED, HOWEVER, that at
the option of the Issuer, payments of principal and interest on the Notes (other
than payments of principal and interest due at Maturity) may be made (i) by
check mailed to the address of the Person entitled thereto as such address shall
appear in the Security Register or (ii) by wire transfer to an account
maintained by the Person entitled thereto located within the United States.

            Section 2.8  CURRENCY.

            Principal and interest on the Notes shall be payable in Dollars.

            Section 2.9  REGISTERED SECURITIES; GLOBAL FORM.

            The Notes shall be issuable and transferable in fully registered
form as Registered Securities, without coupons. The Notes shall each be issued
in the form of one or more permanent Global Securities. The depository for the
Notes shall be The Depository Trust Company ("DTC"). The Notes shall not be
issuable in definitive form except as provided in Section 305 of the Original
Indenture.

            Section 2.10  FORM OF NOTES.

            The Notes shall be substantially in the form attached as EXHIBIT A
hereto.

            Section 2.11  REGISTRAR AND PAYING AGENT.

            The Trustee shall initially serve as Security Registrar and Paying
Agent for the Notes.

            Section 2.12  DEFEASANCE.

             The provisions of Sections 1402 and 1403 of the Original Indenture,
together with the other provisions of Article Fourteen of the Original
Indenture, shall be applicable to the Notes. The provisions of Section 1403 of
the Original Indenture shall apply to the covenants set forth in Sections 2.4
and 2.15 of this Supplemental Indenture and to those covenants specified in
Section 1403 of the Original Indenture.

                                       9
<PAGE>

            Section 2.13  EVENTS OF DEFAULT

            The provisions of clause (5) of Section 501 of the Original
Indenture as applicable with respect to the Notes shall be deemed to be amended
and restated in their entirety to read as follows:

            (5) default under any bond, debenture, note, mortgage, indenture or
instrument under which there may be issued or by which there may be secured or
evidenced any indebtedness (other than non-recourse indebtedness) for money
borrowed by the Issuer (or by any Subsidiary, the repayment of which the Issuer
has guaranteed or for which the Issuer is directly responsible or liable as
obligor or guarantor), having an aggregate principal amount outstanding of at
least $10,000,000, whether such recourse indebtedness now exists or shall
hereafter be created, which default shall have resulted in such indebtedness
becoming or being declared due and payable prior to the date on which it would
otherwise have become due and payable, without such indebtedness having been
discharged, or such acceleration having been rescinded or annulled, within a
period of 10 days after there shall have been given written notice, by
registered or certified mail, to the Issuer by the Trustee or to the Issuer and
the Trustee by the Holders of at least a majority in principal amount of the
Outstanding Securities of that series specifying such default and requiring the
Issuer to cause such indebtedness to be discharged or cause such acceleration to
be rescinded or annulled and stating that such notice is a "Notice of Default"
hereunder; or


            Section  2.14  ACCELERATION OF MATURITY; RESCISSION AND ANNULMENT.

            The provisions of the first paragraph of Section 502 of the Original
Indenture as applicable with respect to the Notes shall be deemed to be amended
and restated in their entirety to read as follows:

            If an Event of Default with respect to Securities of any series at
the time Outstanding occurs and is continuing, then in every such case the
Trustee or the Holders of not less than a majority in principal amount of the
Outstanding Securities of that series may declare the principal (or, if any
Securities are Original Issue Discount Securities

                                       10
<PAGE>

or Indexed Securities, such portion of the principal as may be specified in the
terms thereof) of all the Securities of that series to be due and payable
immediately, by a notice in writing to the Issuer (and to the Trustee if given
by the Holders), and upon any such declaration such principal or specified
portion thereof shall become immediately due and payable. If an Event of Default
with respect to the Securities of any series set forth in Section 501(6) or (7)
of the Original Indenture occurs and is continuing, then in every such case all
the Securities of that series shall become immediately due and payable, without
notice to the Issuer, at the principal amount thereof (or, if any Securities are
Original Issue Discount Securities or Indexed Securities, such portion of the
principal as may be specified in the terms thereof) plus accrued interest to the
date the Securities of that series are paid plus the Make-Whole Premium, if any,
on the Securities of that series.

            Section 2.15  PROVISION OF FINANCIAL INFORMATION.

            Whether or not the Issuer is subject to Section 13 or 15(d) of the
Exchange Act, the Issuer will, to the extent permitted under the Exchange Act,
file with the Commission the annual reports, quarterly reports and other
documents which the Issuer would have been required to file with the Commission
pursuant to such Section 13 or 15(d) if the Issuer were so subject, such
documents to be filed with the Commission on or prior to the respective dates
(the "Required Filing Dates") by which the Issuer would have been required so to
file such documents if the Issuer were so subject.

            The Issuer will also in any event (x) within 15 days of each
Required Filing Date (i) if the Issuer is not then subject to Section 13 or
15(d) of the Exchange Act, transmit by mail to all Holders, as their names and
addresses appear in the Security Register, without cost to such Holders, copies
of the annual reports and quarterly reports which the Issuer would have been
required to file with the Commission pursuant to Section 13 or 15(d) of the
Exchange Act if the Issuer were subject to such Sections, and (ii) file with the
Trustee copies of annual reports, quarterly reports and other documents which
the Issuer would have been required to file with the Commission pursuant to
Section 13 or 15(d) of the Exchange Act if the Issuer were subject to such
Sections and (y) if filing such documents by the Issuer with the Commission is
not permitted under the Exchange Act, promptly upon written request and payment
of the reasonable cost of duplication and delivery, supply copies of such
documents to any prospective Holder.

            Section 2.16  WAIVER OF CERTAIN COVENANTS.

            Notwithstanding the provisions of Section 1010 of the Original
Indenture, the Issuer may omit in any particular instance to comply with any
term, provision or condition set forth in the Original Indenture and in this
Supplemental Indenture and with any other term, provision or condition with
respect to the Notes (except any such term, provision or condition which could
not be amended without the consent of all Holders of the Notes), if before or
after the time for such compliance the Holders of at least a majority in
principal amount of all Outstanding Notes by Act of such Holders, either waive
such compliance in such instance or generally waive compliance with such
covenant or condition. Except to the extent so expressly waived, and until such
waiver shall become effective, the obligations of the Issuer and the duties of
the Trustee in respect of any such term, provision or condition shall remain in
full force and effect.

                                       11
<PAGE>

            Section 2.17  NO GUARANTY BY THE CORPORATION.

            The Guarantee set forth in Article Sixteen of the Original Indenture
shall not be in effect with respect to the Notes.


                                  ARTICLE THREE

                            MISCELLANEOUS PROVISIONS

            SECTION 3.1.  RATIFICATION OF ORIGINAL INDENTURE.

            Except as expressly modified or amended hereby, the Original
Indenture continues in full force and effect and is in all respects confirmed
and preserved.

            SECTION 3.2.  GOVERNING LAW.

            This Supplemental Indenture and each Note shall be governed by and
construed in accordance with the laws of the State of New York. This
Supplemental Indenture is subject to the provisions of the Trust Indenture Act
of 1939, as amended, and shall, to the extent applicable, be governed by such
provisions.

            SECTION 3.3.  COUNTERPARTS.

            This Supplemental Indenture may be executed in any number of
counterparts, each of which so executed shall be deemed to be an original, but
all such counterparts shall together constitute but one and the same instrument.

            SECTION 3.4.  CERTAIN RIGHTS OF TRUSTEE.

            Except as otherwise expressly provided herein, no duties,
responsibilities or liabilities are assumed, or shall be construed to be
assumed, by the Trustee by reason of this Supplemental Indenture. This
Supplemental Indenture is executed and accepted by the Trustee subject to all
the terms and conditions set forth in the Original Indenture with the same force
and effect as if those terms and conditions were repeated at length herein and
made applicable to the Trustee with respect hereto.

            SECTION 3.5.  TRUSTEE NOT RESPONSIBLE.

            The Trustee shall not be responsible in any manner for or in respect
of the validity or sufficiency of this Supplemental Indenture.

                                       12
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed by their respective officers hereunto duly
authorized, all as of the day and year first written above.

                                   MACK-CALI REALTY, L.P.

                                   By:  Mack-Cali Realty Corporation, its
                                        General Partner



                                   By: /s/ Roger W. Thomas
                                       --------------------------
                                       Name: Roger W. Thomas
                                       Title: Executive Vice President
                                              and General Counsel

Attest: /s/ Daniel J. Wagner
        --------------------
Name: Daniel J. Wagner
Title: Assistant Secretary


                                    WILMINGTON TRUST COMPANY,
                                    as Trustee


                                     By: /s/ James D. Nesci
                                        ---------------------------
                                         Name: James D. Nesci
                                         Title: Authorized Signer


                                       13
<PAGE>

                                                          EXHIBIT A TO
                                                          SUPPLEMENTAL INDENTURE

UNLESS THIS SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), 55 WATER STREET, NEW
YORK, NEW YORK, TO THE ISSUER (AS DEFINED BELOW) OR ITS AGENT FOR REGISTRATION
OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN
THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER
ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER,
PLEDGE, OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS
WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.

THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING SET FORTH IN THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF DTC OR A NOMINEE OF
DTC. THIS SECURITY IS EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A
PERSON OTHER THAN DTC OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED
IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY DTC TO A
NOMINEE OF DTC OR ANOTHER NOMINEE OF DTC OR BY DTC OR ITS NOMINEE TO A SUCCESSOR
DEPOSITORY OR ITS NOMINEE.

Registered No. 1                                PRINCIPAL AMOUNT
CUSIP No.: 55448Q AD 8                          $15,000,000

                        MACK-CALI REALTY, L.P.

                         7.835% NOTE DUE 2010


            MACK-CALI REALTY, L.P., a limited partnership duly organized and
existing under the laws of the State of Delaware (herein referred to as the
"ISSUER" which term shall include any Successor Person under the Indenture
hereinafter referred to), for value received, hereby promises to pay to CEDE &
CO., or registered assigns, upon presentation, the principal sum of 15,000,000
DOLLARS on December 15, 2010, and to pay interest on the outstanding principal
amount thereon from December 21, 2000, or from the immediately preceding
Interest Payment Date to which interest has been paid or duly provided for,
semi-annually in arrears on June 15 and December 15 in each year, commencing
June 15, 2001, at the rate of 7.835% per annum, until the entire principal
hereof is paid or made available for payment. The interest so payable and
punctually paid or duly provided for on any Interest Payment Date will, as
provided in the Indenture, be paid to the Person in whose name this Security is
registered at the close of business on the Regular Record Date for such interest
which shall be the June 1 or December 1 (whether or not a Business Day), as the
case may be, next preceding such Interest Payment Date. Any such interest not so

                                       A-1
<PAGE>

punctually paid or duly provided for shall forthwith cease to be payable to the
Holder on such Regular Record Date, and may either be paid to the Person in
whose name this Security is registered at the close of business on a Special
Record Date for the payment of such Defaulted Interest to be fixed by the
Trustee, notice whereof shall be given to Holders of the Securities not more
than 15 days and not less than 10 days prior to such Special Record Date, or may
be paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Securities may be listed,
and upon such notice as may be required by such exchange, all as more fully
provided in the Indenture. Payment of the principal of and interest on this
Security will be made at the office or agency maintained for that purpose in the
City of Wilmington, Delaware or elsewhere as provided in the Indenture, in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts; PROVIDED, HOWEVER, that at
the option of the Issuer payments of principal and interest on the Notes (other
than payments of principal and interest due at Maturity) may be made (i) by
check mailed to the address of the Person entitled thereto as such address shall
appear in the Security Register or (ii) by wire transfer to an account of the
Person entitled thereto located within the United States.

            Securities of this series are one of a duly authorized issue of
securities of the Issuer (herein called the "SECURITIES"), issued and to be
issued in one or more series under an Indenture, dated as of March 16, 1999,
among the Issuer, Mack-Cali Realty Corporation and Wilmington Trust Company,
(herein called the "TRUSTEE", which term includes any successor trustee under
the Indenture), as supplemented by Supplemental Indenture No. 1, dated as of
March 16, 1999, as further supplemented by Supplemental Indenture No. 2, dated
as of August 2, 1999, and as further supplemented by Supplemental Indenture No.
3, dated as of December 21, 2000 (as so supplemented, herein called the
"INDENTURE"), between the Issuer and the Trustee to which Indenture and all
indentures supplemental thereto reference is hereby made for a statement of the
respective rights, limitations of rights, duties and immunities thereunder of
the Issuer, the Trustee and the Holders of the Securities and of the terms upon
which the Securities are authenticated and delivered. This Security is one of
the series designated in the first page thereof, limited in aggregate principal
amount to $15,000,000.

            Securities of this series may be redeemed at any time at the option
of the Issuer, in whole or in part, upon notice of not more than 60 nor less
than 30 days prior to the Redemption Date, at a redemption price equal to the
sum of (i) the principal amount of the Securities being redeemed plus accrued
and unpaid interest thereon up to but not including the Redemption Date and (ii)
the Make-Whole Premium, if any, with respect to such Securities.

            The Indenture contains provisions for defeasance at any time of (a)
the entire indebtedness of the Issuer on this Security and (b) certain
restrictive covenants and the related defaults and Events of Default applicable
to the Issuer, in each case,

                                      A-2
<PAGE>

upon compliance by the Issuer with certain conditions set forth in the
Indenture, which provisions apply to this Security.

            If an Event of Default with respect to the Securities shall occur
and be continuing, the principal of the Securities may be declared due and
payable in the manner and with the effect provided in the Indenture.

            As provided in and subject to the provisions of the Indenture, the
Holder of this Security shall not have the right to institute any proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder, unless such Holder shall have previously given
written notice to the Trustee of a continuing Event of Default with respect to
the Securities, the Holders of not less than a majority in principal amount of
the Securities of this series at the time Outstanding shall have made written
request to the Trustee to institute proceedings in respect of such Event of
Default as Trustee and offered the Trustee reasonable indemnity and the Trustee
shall not have received from the Holders of a majority in principal amount of
Securities of this series at the time Outstanding a direction inconsistent with
such request, and shall have failed to institute any such proceeding, for 60
days after receipt of such notice, request and offer of indemnity. The foregoing
shall not apply to any suit instituted by the Holder of this Security for the
enforcement of any payment of principal hereof or any interest on or after the
respective due dates expressed herein.

            The Indenture permits, with certain exceptions as therein provided,
the amendment thereof and the modification of the rights and obligations of the
Issuer and the rights of the Holders of the Securities of each series to be
affected under the Indenture at any time by the Issuer and the Trustee with the
consent of the Holders of not less than a majority in principal amount of the
Outstanding Securities of each series of Securities then Outstanding affected
thereby. The Indenture also contains provisions permitting the Holders of
specified percentages in principal amount of the Securities of each series at
the time Outstanding, on behalf of the Holders of all Securities of such series,
to waive compliance by the Issuer with certain provisions of the Indenture and
certain past defaults under the Indenture and their consequences. Any such
consent or waiver by the Holder of this Security shall be conclusive and binding
upon such Holder and upon all future Holders of this Security and of any
Security issued upon the registration of transfer hereof or in exchange herefor
or in lieu hereof, whether or not notation of such consent or waiver is made
upon this Security.

            No reference herein to the Indenture and no provision of this
Security or of the Indenture shall alter or impair the obligation of the Issuer,
which is absolute and unconditional, to pay the principal of (and Make-Whole
Premium, if any) and interest on this Security at the times, place and rate, and
in the coin or currency, herein prescribed.

                                      A-3
<PAGE>

            As provided in the Indenture and subject to certain limitations
therein set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office or agency of the Issuer in any Place of Payment where the principal of
(and Make-Whole Premium, if any) and interest on this Security are payable, duly
endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Issuer and the Security Registrar duly executed by the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Securities of this series, of authorized denominations and for the same
aggregate principal amount, will be issued to the designated transferee or
transferees.

            Except as set forth in Section 302 of the Indenture, the Securities
of this series are issuable only in registered form without coupons in
denominations of $1,000 and any integral multiple thereof. As provided in the
Indenture and subject to certain limitations therein set forth, Securities of
this series are exchangeable for a like aggregate principal amount of Securities
of this series of a different authorized denomination, as requested by the
Holder surrendering the same.

            No service charge shall be made for any such registration of
transfer or exchange, but the Issuer may require payment of a sum sufficient to
cover any tax or other governmental charge payable in connection therewith.

            Prior to due presentment of this Security for registration of
transfer, the Issuer, the Trustee and any agent of the Issuer or the Trustee may
treat the Person in whose name this Security is registered as the owner hereof
for all purposes, whether or not this Security be overdue, and neither the
Issuer, the Trustee nor any such agent shall be affected by notice to the
contrary.

            No recourse under or upon any obligation, covenant or agreement
contained in the Indenture or in this Security, or because of any indebtedness
evidenced hereby or thereby, shall be had against any promoter, as such, or
against any past, present or future shareholder, officer or director, as such,
of the Issuer or of any successor, either directly or through the Issuer or any
successor, under any rule of law, statute or constitutional provision or by the
enforcement of any assessment or by any legal or equitable proceeding or
otherwise, all such liability being expressly waived and released by the
acceptance of this Security by the Holder thereof and as part of the
consideration for the issue of the Securities of this series.

            All capitalized terms used in this Security which are defined in the
Indenture shall have the meanings assigned to them in the Indenture.

            THE INDENTURE AND THE SECURITIES, INCLUDING THIS SECURITY, SHALL BE
GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

                                      A-4
<PAGE>

            Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures, the Issuer has caused "CUSIP" numbers to be
printed on the Securities of this series as a convenience to the Holders of such
Securities. No representation is made as to the correctness or accuracy of such
CUSIP numbers as printed on the Securities, and reliance may be placed only on
the other identification numbers printed hereon.

            Unless the certificate of authentication hereon has been executed by
or on behalf of the Trustee by manual signature, this Security shall not be
entitled to any benefit under the Indenture or be valid or obligatory for any
purpose.


      [REMAINDER OF PAGE INTENTIONALLY BLANK; SIGNATURE PAGE FOLLOWS]

                                      A-5
<PAGE>

            IN WITNESS WHEREOF, MACK-CALI REALTY, L.P. has caused this
instrument to be duly executed.

Dated: December 21, 2000

                                    MACK-CALI REALTY, L.P.

                                    By:  Mack-Cali Realty Corporation, its
                                         General Partner


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


Name:
Title:


TRUSTEE'S CERTIFICATE OF AUTHENTICATION:

            This is one of the Securities of the series designated therein
referred to in the within-mentioned Indenture.

                                    WILMINGTON TRUST COMPANY,
                                       as Trustee


                                       By:
                                          --------------------------------------
                                          Authorized Signatory

                                      A-6
<PAGE>

================================================================================

                                 ASSIGNMENT FORM

                   FOR VALUE RECEIVED, the undersigned hereby
                        sells, assigns and transfers unto

  PLEASE INSERT SOCIAL
  SECURITY OR OTHER IDENTIFYING
  NUMBER OF ASSIGNEE
------------------------------------
                                     ................................
------------------------------------

 .....................................................................
         (Please Print or Typewrite Name and Address including
                         Zip Code of Assignee)

 .....................................................................
the within Security of Mack-Cali Realty, L.P. and hereby does irrevocably
constitute and appoint

 ............................................................ Attorney
to transfer said Security on the books of the within-named Issuer with
full power of substitution in the premises.

Dated:  ..............  .............................................

                        .............................................

NOTICE: The signature to this assignment must correspond with the name as it
appears on the first page of the within Security in every particular, without
alteration or enlargement or any change whatever.

                        Signature(s) must be guaranteed by an institution which
                        is a member of one of the following recognized signature
                        Guarantee Programs: (i) The Securities Transfer Agent
                        Medallion Program (STAMP); (ii) The New York Stock
                        Exchange Medallion Program (MNSP); (iii) The Stock
                        Exchange Medallion Program (SEMP); or (iv) another
                        guarantee program acceptable to the Trustee.


                              -------------------------------
                               Signature Guarantee

================================================================================

                                      A-7