<PAGE>   1
                                                                EXHIBIT 10.35

            [ "..." indicates material has been omitted pursuant to a
     Confidential Treatment Request, which the Company has filed separately
                  with the Securities and Exchange Commission]

                                               COVANCE BIOTECHNOLOGY SERVICES
                                               3000 WESTON PARKWAY
                                               CARY, NC 27513-2300
                                               TEL: (919) 388-5700
                                               FAX: (919) 678-0366
C O V A N C E
THE DEVELOPMENT SERVICES COMPANY



August 30, 1999

John W. Holaday, Ph.D., FCCM
Chairman & Chief Executive
EntreMed, Inc.
9640 Medical Center Drive, Suite 200
Rockville, MD 20850

                                LETTER OF INTENT

This letter constitutes formal notification of EntreMed, Inc.'s (EntreMed)
intent to retain Covance Biotechnology Services, Inc. (Covance) to perform
manufacturing services for clinical production of approximately "..." of
EntreMed's Endostatin(TM) beginning in "...".

"...". Upon signing this letter, Covance and EntreMed are committing to
Endostatin production in "..." and EntreMed commits to pay for the
Endostatin(TM) produced.

The Endostatin(TM) production anticipated to begin in "..." will be performed
under an Amendment or Change Order to the current Agreement (Bioprocessing
Services Agreement dated October 16, 1998). Such Amendment or Change Order will
incorporate the following terms:

-     EntreMed agrees to purchase "..." of Endostatin(TM) for "...".

-     The price "..." for the Endostatin(TM) produced in this campaign will be
      "...". The first "..." of this campaign are "...". "...". "...".

-     The Endostatin(TM) production will begin as soon as possible following the
      completion of the on-going process development work to improve the
      fermentation and purification processes for Endostatin(TM) (Change Order
      "..." and Change Order "..." to the existing Agreement). EntreMed has also
      requested that Covance manufacture Angiostatin(R) up to the time the
      Endostatin(TM) campaign needs to begin and any additional amounts of
      Angiostatin(R) produced beyond the contracted "..." will be "...". The
      current earliest date for completion of the process development work and
      its incorporation into the "..." process is "...".




<PAGE>   2
          [ "..." indicates material has been omitted pursuant to a
    Confidential Treatment Request, which the Company has filed separately
                 with the Securities and Exchange Commission]


C O V A N C E
THE DEVELOPMENT SERVICES COMPANY


-     The manufacturing process employed in this "..." campaign will include, to
      the extent possible, the process improvements identified by the on-going
      process development work.

-     Covance will ship bulk Endostatin(TM) to "..." for vialing. Vialing of the
      first "...". Vialing of the subsequent "...".

-     Covance will use its best efforts to release "..." of vialed
      Endostatin(TM) for "..." by "..." using the above schedule.


EntreMed and Covance recognize that this Letter of Intent is necessary to allow
for immediate prioritization of activities at Covance to switch from "..." to
Endostatin(TM), and to allow Covance to "...".

Upon signature of the necessary Change Orders or Amendments to the current
Bioprocessing Services Agreements for Endostatin(TM) (dated October 16, 1998)
and Angiostatin(R) (dated July 7, 1999) as anticipated under this
Letter-of-Intent, Covance agrees to provide Endostatin(TM) batches "..." and
"..." to EntreMed "...".


Signatures below indicate acceptance of the above mentioned terms.



 /s/  V. BRYAN LAWLIS                        /s/  JOHN W. HOLADAY
----------------------------                 ----------------------------------
V. Bryan Lawlis, Ph.D.                       John W. Holaday, Ph.D., FCCM
Chairman                                     Chairman & Chief Executive Officer
Covance Biotechnology Services Inc.          EntreMed, Inc.

Date:       9/1/99                           Date:       8/31/99
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