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                                                                   EXHIBIT 10.5


                                  MORTGAGE NOTE


$136,100,000                                                 June 8, 1998

                FOR VALUE RECEIVED, the undersigned, ARDEN REALTY FINANCE III,
L.L.C., a Delaware limited liability company ("MAKER"), promises to pay to the
order of LEHMAN BROTHERS REALTY CORPORATION, a Delaware corporation, its
successors and assigns ("HOLDER"), at such place as Holder may from time to time
designate in writing, the principal sum of ONE HUNDRED THIRTY-SIX MILLION ONE
HUNDRED THOUSAND AND NO/100 DOLLARS ($136,100,000.00) in lawful money of the
United States of America, together with interest thereon, to be computed and
paid as specified in SECTION 1 below.

                Except as otherwise defined or limited herein, capitalized terms
used herein shall have the meanings ascribed to them in that certain Loan
Agreement (the "LOAN AGREEMENT") dated as of the date hereof by and between
Maker and Holder. This is the Mortgage Note referred to in the Loan Agreement.


1.      PAYMENTS OF PRINCIPAL AND INTEREST.

        1.1     INTEREST; MATURITY DATE

                The outstanding principal balance hereof from time to time shall
bear interest (a) on or prior to April 16, 2008 (the "Anticipated Repayment
Date"), at a rate per annum equal to six and 74/100 percent (6.74%) (the "Base
Rate") and (b) from and after April 17, 2008, at a rate per annum (the "Adjusted
Interest Rate") equal to the greater of (i) eleven and 74/100 percent (11.74%)
and (ii) the sum of (A) five percentage points (5%) and (B) the average,
calculated by linear interpolation (rounded to three decimal places), of the
yields of the United States Treasury Constant Maturities with the terms (one
longer and one shorter) most nearly approximating those of U.S. Obligations
having maturities as close as possible to the 20th anniversary of the
Anticipated Repayment Date, as determined by the Holder on the basis of Federal
Reserve Statistical Release H.15-Selected Interest Rates under the heading U.S.
Governmental Security/Treasury Constant Maturities, or such other recognized
source of financial market information as may reasonably be selected by the
Holder, in each case on the last Business Day of the week immediately prior to
the Anticipated Repayment Date. Interest accrued from the date hereof to (and
including) June 30, 1998 shall be due and payable on July 1, 1998. Thereafter,
payments of interest or principal and interest, as applicable, and other amounts
to be paid hereunder shall be made, in arrears, on the first (1st) day of each
calendar month, or, if in any calendar month the first (1st) day is not a
Business Day, then on the Business Day succeeding the first (1st) day,
commencing August 1, 1998 (each, a "Due Date") for the period (the "Debt Service
Period") beginning on (and including) the first (1st) day of the calendar month
immediately preceding the month in which such Due Date occurs, through (but
excluding) the Due Date. Interest shall be computed on the basis of a 360 day
year and the actual number of days elapsed in each Debt Service Period.


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                For the period that commences on the date hereof and ends on
April 16, 2003 (the "Interest Only Period"), Holder shall pay interest only on
the outstanding principal balance hereof. On each Due Date after the expiration
of the Interest Only Period, Maker shall pay to Holder a monthly payment of
principal and interest (the "Scheduled Principal and Interest Payment") in an
amount equal to the amount of the monthly payment that would be necessary to
fully amortize the outstanding principal balance of the Loan as of the last day
of the Interest Only Period over a 25-year period assuming a rate of interest
per annum equal to the Base Rate (with interest calculated on the basis of
actual number of days elapsed and a 360 day year).

                Following the Anticipated Repayment Date, interest on the
outstanding principal balance hereof shall continue to accrue at the Base Rate
and Maker shall continue to make the Scheduled Principal and Interest Payment on
each Due Date.

                Payment of all interest accruing in respect of this Mortgage
Note after the Anticipated Repayment Date in the amount equal to the difference
between the amount that accrues at the Adjusted Interest Rate and the amount
that is paid (whether as part of the Scheduled Principal and Interest Payment,
if applicable, or otherwise) at the Base Rate ("Accrued Interest") shall be (a)
deferred, (b) added to the principal amount of this Mortgage Note, and (c) to
the extent permitted by applicable law, accrue interest at the Adjusted Interest
Rate. If not sooner paid, all Accrued Interest together with interest thereon
(to the extent permitted by applicable law) shall be due and payable in full on
the Final Maturity Date (as defined below).

                Subsequent to the Anticipated Repayment Date and in accordance
with the Cash Management Procedures, Maker shall pay to Holder on each Due Date
(without duplication), until the entire Debt is repaid in full, Excess Cash Flow
for the Debt Service Period relating to such Due Date. Each monthly payment of
Excess Cash Flow made by Borrower under this Mortgage Note shall be applied
first to the reduction of the outstanding principal balance of this Mortgage
Note and after the principal balance of this Mortgage Note has been paid in full
to the reduction of the outstanding amount of Accrued Interest (and interest
thereon).

                The outstanding principal balance of this Mortgage Note,
together with accrued and unpaid interest thereon through April 16, 2028
(including any unpaid Accrued Interest and interest thereon) shall be due and
payable on April 16, 2028 (the "Final Maturity Date").

        1.2     PREPAYMENT RESTRICTIONS

                On any Due Date occurring on or after the Anticipated Repayment
Date, all or any portion of the principal balance hereof may be prepaid, at
Maker's option, in full or in part, without penalty or premium; provided,
however, that the requirements of SECTION 2.10 of the Loan Agreement shall have
been satisfied. In addition, a portion of the principal amount hereof may be
prepaid prior to the first day of the Defeasance Period, upon satisfaction of
the conditions in SECTION 2.7 of the Loan Agreement but without payment of a
Yield Maintenance Payment, in connection with a Casualty or Taking (provided
that the Mortgage does not require a Restoration of the applicable Mortgaged
Property). Neither Holder nor, following the Securitization, the 


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Trustee or the Servicer shall be required to accept or apply any prepayment
requiring payment of a Yield Maintenance Payment, as provided in this paragraph
or in SECTION 1.3 hereof, unless such prepayment is accompanied by the payment
of such Yield Maintenance Payment, and if any legal and other expenses are due
and owing to Holder, Trustee or Servicer in connection with such prepayment
under the terms of the Pooling and Servicing Agreement or any Loan Document,
neither Holder nor the Servicer shall be required to accept or apply any
prepayment unless the prepayment also is accompanied by the amount that is due
and payable to Holder, Trustee or Servicer with respect to such expenses. Except
as provided above, this Mortgage Note may not be prepaid.

        1.3     YIELD MAINTENANCE

                If (i) all or any part of the principal amount of the Loan is
prepaid after the Closing Date but prior to the last day of the Defeasance
Period as a result of the acceleration of the maturity of the Mortgage Note
after an Event of Default, Maker shall be required to pay a Yield Maintenance
Payment equal to the greater of (A) 1% of the amount of the principal prepayment
that is to be applied to the outstanding principal balance hereof and (B) the
present value as of the end of the applicable Debt Service Period, discounted at
the Reinvestment Yield, of a series of payments each equal to the Payment
Differential on each of the remaining Due Dates prior to and including the
Anticipated Repayment Date, after giving effect to the regularly scheduled
payment of principal that is to be made on the Prepayment Date. No Yield
Maintenance Payment shall be required in connection with prepayments made on or
after the last day of the Defeasance Period.

                Promptly following acceleration of this Mortgage Note or
following the occurrence of any other event, the occurrence of which obligates
Maker to make a Yield Maintenance Payment, Holder shall notify Maker of the
amount and basis of determination of the Yield Maintenance Payment promptly upon
determining the Treasury Rate, as contemplated below. Absent manifest error,
Maker shall not dispute Holder's calculations hereunder.

                For purposes of this SECTION 1.3, the following terms shall have
the meanings ascribed to them below:

                "PAYMENT DIFFERENTIAL" means, an amount equal to (x) the Base
        Rate, minus the Reinvestment Yield, divided by (y) 12, and multiplied by
        (z) the amount of the principal prepayment.

                "REINVESTMENT YIELD" is the Treasury Rate converted to a monthly
        compounded nominal annual yield.

                "TREASURY RATE" is equal to the lesser of (A) the annual yield
        on the United States Treasury issue (primary issue) with a maturity date
        closest to the Final Maturity Date and (B) the annual yield on the
        United States Treasury issue (primary issue) with a maturity equal to
        the remaining average life of this Mortgage Note with each such yield
        being based on the bid price for such issue as published in The Wall
        Street Journal on the 


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        date that is 14 days prior to (x) the applicable Prepayment Date set
        forth in the notice of prepayment provided by the Maker or (y) the date
        of acceleration by the Holder (or if such bid price is not published on
        that date, the next preceding date on which such bid price is so
        published).

        1.4     METHOD OF PAYMENT; PAYMENTS ABSOLUTE

                All payments due hereunder shall be made in legal currency of
the United States of America in immediately available federal funds by credit to
the Holder's account in the United States as announced by the Holder from time
to time in writing to Maker. If any payment is due on a day that is not a
Business Day, the date for payment thereof shall be extended to the next
Business Day, without additional interest, except that, if the Final Maturity
Date is not a Business Day, the date for payment of the amount, if any, that is
due on the Final Maturity Date shall be extended to the next succeeding Business
Day, and any interest payable thereon shall accrue and be payable for such
extension of time at the Adjusted Interest Rate.

                The terms of this Mortgage Note are hereby supplemented in full
by the terms of the Loan Agreement and the other Loan Documents.

2.      SECURITY FOR THE LOAN.

                This Mortgage Note is secured by, among other things, twenty-two
(22) Mortgaged Properties owned by Maker, including all assets of Maker related
thereto, pursuant to a Mortgage encumbering the Land, the Buildings located
thereon and other Improvements relating to such Buildings and granting a lien on
and security interest in certain other Property described therein, and by other
Security Documents effecting and granting a lien on and security interest in
other Collateral, including but not limited to, the Security Agreement, the
Assignment of Rents and Leases, and the Collateral Assignment of Management
Agreement.

3.      EVENTS OF DEFAULT.

                The entire outstanding principal balance of this Mortgage Note,
together with all accrued and unpaid interest thereon and all other sums due
hereunder or under any of the Loan Documents (all such sums, collectively, the
"DEBT"), or any portion thereof, shall without notice, except such notice as is
required under the terms of any Loan Document, become immediately due and
payable at the option of Holder: (a) if payments of principal, interest and
premium, if any, due hereunder are not made when due or (b) an Event of Default
shall have occurred and be continuing under the Loan Agreement (each of the
foregoing, an "EVENT OF DEFAULT"). In the event that Holder retains counsel to
collect all or any part of the Debt, or to protect or foreclose the security
provided in connection herewith, Maker agrees to pay reasonable costs of
collection incurred by Holder, including reasonable attorneys' fees.

4.      DEFAULT INTEREST; LATE PAYMENT FEE.

                Maker does hereby agree that, if any amount due hereunder is not
paid when due, 


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including, without limitation, Maker's failure to pay the Debt in full on the
Maturity Date or on the date set for acceleration following an Event of Default,
Holder shall be entitled to receive, and Maker shall pay, to the extent
permitted by applicable law, interest to Holder on such past due amounts
beginning on the date such payment becomes past due at a rate of interest equal
to the lesser of (a) the greater of (i) the Base Rate plus three percentage
points (3%) (or, on and after the Anticipated Repayment Date, the Adjusted
Interest Rate plus three percentage points (3%)) and (ii) the Prime Rate plus
two percentage points (2%), and (b) the maximum rate of interest allowed to be
collected under applicable law.

                In addition to Default Interest, in the event Borrower fails to
make any payment of interest, Yield Maintenance Payment or other payment
hereunder when due, Borrower shall be liable for the payment of a late charge
equal to five percent (5%) of the amount of the payment; provided, however,
prior to a Securitization, Borrower shall not be liable to pay such a late
payment fee the first time Borrower fails to make a Monthly Debt Service Payment
when due.

5.      LIMITATIONS ON RECOURSE.

                Notwithstanding any contrary provision in this Mortgage Note or
any of the Loan Documents, it is hereby expressly agreed that, except as
otherwise provided in this SECTION 5 or in any section of any Loan Document that
is substantially similar to this SECTION 5, there shall be no recourse to the
assets of Maker or any of its Members (other than against the Collateral and any
other property given as security for the payment of this Mortgage Note) for (i)
the payment of principal, interest, Defeasance Deposits, Yield Maintenance
Payments or other charges hereunder or for any other amount that is or may
become due and owing to Holder by Maker under this Mortgage Note or any of the
other Loan Documents or (ii) the performance or discharge of any covenant or
undertaking hereunder or under the other Loan Documents, and in the event of any
Event of Default hereunder or thereunder, Holder agrees to proceed solely
against the Collateral and any other property given as security for payment of
this Mortgage Note, and Holder shall not seek or claim recourse against Maker or
any Member (other than against the Collateral and any other property given as
security for payment of this Mortgage Note) for any deficiency or for any
personal judgment after a foreclosure of the lien of the Mortgage or other
Security Documents or for the performance or discharge of any covenants or
undertakings of Maker hereunder or under any other Loan Documents (except that
Maker may be made a party to a proceeding to the extent legally necessary for
the conduct of a foreclosure or the exercise of other similar remedies under the
Mortgage or other Security Documents). Notwithstanding the foregoing, nothing
contained in this SECTION 5 shall relieve Maker or any Member of any personal
liability for any loss, cost, expense, damage or liability arising or resulting
from (A) any breach of any representation or warranty made in the Loan Agreement
that was materially incorrect when made and that was made with fraudulent
intent, (B) any amount paid or distributed to the Members, the Manager or any
Affiliate of any of them in violation of the provisions of the Loan Documents,
(C) fraud or breach of trust, including misapplication of Loan proceeds or any
Insurance Proceeds or Awards or other sums that are part of the Collateral that
may come into the possession or control of Maker or a Member or any Affiliate of
any of them, (D) liability under the Environmental Indemnity Agreement or (E)


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following the occurrence of a Lockbox Event, the willful failure of Maker to
instruct Tenants of the Mortgaged Properties to make payments of Rents into the
Lockbox Account or the failure of Maker or the Manager to deposit payments of
Rents received by Maker or Manager into the Lockbox Account promptly upon
receipt thereof. It is hereby expressly agreed that no director, officer,
shareholder, partner, member or employee of Maker or any Member, nor the legal
or personal representative, successor or assign of any of the foregoing, nor any
other principal of Maker or any Member, whether disclosed or undisclosed, shall
have any personal liability under the Loan Agreement or any of the other Loan
Documents, except as personal liability may be specifically imposed upon a
signatory to any of the Loan Documents. It is the intention of the parties
hereto that this SECTION 5 shall govern every other provision of the Loan
Documents and that the absence of explicit reference to this SECTION 5 in any
provision of the Loan Documents or the absence of any Section similar to this
SECTION 5 in any Loan Document shall not be construed to deny the application of
this SECTION 5 to such provision, notwithstanding the presence of explicit
reference to this SECTION 5 in other provisions of the Loan Documents.

6.      NO USURY.

                It is expressly stipulated and agreed to be the intent of Maker
and Holder at all times to comply with applicable state law and with applicable
United States federal law (to the extent that it permits Holder to contract for,
charge, take, reserve, or receive a greater amount of interest than under state
law) and that this Section shall control every other covenant and agreement in
this Mortgage Note and the other Loan Documents. If the applicable law (state or
federal) is ever judicially interpreted so as to render usurious any amount
called for under this Mortgage Note or under any of the other Loan Documents, or
contracted for, charged, taken, reserved, or received with respect to the Debt,
or if Holder's exercise of the option to accelerate the maturity of this
Mortgage Note, or if any prepayment by Maker results in Maker having paid any
interest in excess of that permitted by applicable law, then it is Maker's and
Holder's express intent that all excess amounts theretofore collected by Holder
shall be credited to the principal balance hereof and all other debt in the
order specified above (or, if this Mortgage Note and all other Debt have been or
would thereby be paid in full, shall be refunded to Maker), and the provisions
of this Mortgage Note and the other Loan Documents shall immediately and
automatically be deemed to be reformed, and the amounts thereafter collectible
hereunder and thereunder reduced, without the necessity of the execution of any
new documents, so as to comply with the applicable law, but so as to permit the
recovery of the fullest amount otherwise called for hereunder or thereunder. All
sums paid or agreed to be paid to Holder for the use, forbearance, or detention
of the Debt shall, to the fullest extent permitted by applicable law, be
amortized, prorated, allocated, and spread throughout the full stated term of
the Debt until payment in full so that the rate or amount of interest on account
of the Debt does not exceed the maximum lawful rate from time to time in effect
and applicable to the Debt for so long as the Debt is outstanding.

7.      AUTHORITY.

                Maker represents that Maker has full power, authority and legal
right to execute 


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and deliver this Mortgage Note and to perform its obligations hereunder, and
that this Mortgage Note constitutes the valid and binding obligation of Maker,
enforceable against Maker in accordance with its terms, except as enforceability
may be limited by (i) applicable bankruptcy, insolvency, reorganization,
moratorium, or similar laws affecting the enforcement of creditors' rights
generally and (ii) general principles of equity, regardless of whether
considered in proceedings at law or in equity.

8.      NOTICES.

                All notices or other communications required or permitted to be
given pursuant hereto shall be given in the manner specified in the Loan
Agreement directed to the parties at their respective addresses as provided
therein.

9.      WAIVER OF JURY TRIAL.

                MAKER, AND BY ACCEPTANCE HEREOF, HOLDER, EACH (1) COVENANTS AND
AGREES NOT TO ELECT TRIAL BY JURY OF ANY ISSUE TRIABLE OF RIGHT BY A JURY, AND
(2) WAIVES ANY RIGHTS TO TRIAL BY JURY TO THE FULL EXTENT THAT ANY SUCH RIGHT
SHALL NOW OR HEREAFTER EXIST. THIS WAIVER OF RIGHT TO TRIAL BY JURY IS
SEPARATELY GIVEN, KNOWINGLY AND VOLUNTARILY, BY EACH PARTY HERETO, AND THIS
WAIVER IS INTENDED TO ENCOMPASS INDIVIDUALLY EACH INSTANCE AND EACH ISSUE AS TO
WHICH THE RIGHT TO A JURY TRIAL WOULD OTHERWISE ACCRUE. THE PARTIES ARE HEREBY
AUTHORIZED TO SUBMIT THIS MORTGAGE NOTE TO ANY COURT HAVING JURISDICTION OVER
THE SUBJECT MATTER TO BE TRIED SO AS TO SERVE AS CONCLUSIVE EVIDENCE OF THE
OTHER PARTY'S HEREIN CONTAINED WAIVER OF THE RIGHT TO JURY TRIAL. FURTHER, EACH
PARTY HERETO CERTIFIES THAT NO REPRESENTATIVE OF THE OTHER PARTY (INCLUDING SUCH
OTHER PARTY'S COUNSEL) HAS REPRESENTED, EXPRESSLY OR OTHERWISE, TO THAT PARTY,
THAT THE OTHER PARTY WILL NOT SEEK TO ENFORCE THIS WAIVER BY SUCH CERTIFYING
PARTY OF THE RIGHT TO A JURY TRIAL.

10.     GOVERNING LAW.

                This Mortgage Note shall be governed by and construed under and
in accordance with the laws of the State of New York, excluding the choice of
law rules thereof.

11.     MISCELLANEOUS.

                (a)     No release of any security for the Debt or any person
liable for payment of the Debt, no extension of time for payment of this
Mortgage Note or any installment hereof, and no alteration, amendment or waiver
of any provision of the Loan Documents made by agreement between Holder and any
other person or party shall release, modify, amend, waive, extend, change,
discharge, terminate or affect the liability of Maker or any other person or
party who 


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might be or become liable for the payment of all or any part of the Debt, under
the Loan Documents.

                (b)     Maker and all others who may become liable for the
payment of all or any part of the Debt do hereby severally waive presentment and
demand for payment, notice of dishonor, protest, notice of protest, notice of
non-payment, and notice of intent to accelerate the maturity hereof and of
acceleration.

                (c)     This Mortgage Note may not be modified, amended, waived,
extended, changed, discharged or terminated orally or by any act or failure to
act on the part of Maker or Holder, but only by an agreement in writing signed
by the party against whom enforcement of any modification, amendment, waiver,
extension, change, discharge or termination is sought.

                (d)     Whenever used, the singular number shall include the
plural, the plural the singular, and the words "Holder" and "Maker" shall
include their respective successors, assigns, heirs, executors and
administrators.

                           [SIGNATURE PAGE TO FOLLOW]


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                IN WITNESS WHEREOF, Maker has duly executed or has caused its
duly authorized officer to execute this Mortgage Note on its behalf, as of the
day and year first above written.

                                       MAKER:

                                       ARDEN REALTY FINANCE III, L.L.C.,
                                       a Delaware limited liability company


                                       By:
                                       Name:
                                       Its:


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