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                                                               EXHIBIT NO. 10.55

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.


EYETECH PHARMACEUTICALS

                                                      500 Seventh Avenue
                                                      18(th) Floor
                                                      New York, New York 10018
                                                      August 29, 2003


Raylo Chemicals Inc.
8045 Argyll Road
Edmonton, Alberta
Canada
Attn:  Matt Colomb
       Greg Klak
       Robin Nicol

Gentlemen:

      This Letter of Understanding ("LOU") is agreed to and accepted by and
between Eyetech Pharmaceuticals, Inc., a Delaware corporation ("Eyetech") and
Raylo Chemicals, Inc., a company organized and existing under the laws of Canada
("Raylo"), and sets forth the intentions, terms and conditions pursuant to which
Eyetech and Raylo will undertake actions to allocate between themselves control
of the technical and operational aspects of the manufacture of Eyetech's
proprietary compound Macugen(TM) during the period that this LOU remains in
effect. This LOU shall take effect on September 1, 2003 and remain in effect
until the earlier of such time as (a) this LOU is terminated by joint agreement
between Eyetech and Raylo after satisfaction of certain mutually agreed to
performance targets for the Macugen(TM) production at Raylo or (b) the parties
discontinue any relationship between them whereby Raylo manufactures Eyetech's
Macugen(TM) compound for Eyetech at Raylo's facility.

      During the period that this LOU is in effect, the parties hereto envision
entering into a definitive Manufacturing and Supply Agreement (the "Proposed
Agreement") setting forth certain agreements between them relating to a proposed
long term manufacturing relationship whereby Raylo would manufacture the
Macugen(TM) compound for Eyetech.
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      Eyetech and Raylo agree as follows:

1.    Allocation of Responsibility and Authority for Production of Macugen(TM)

      -     Eyetech will assume responsibility for and have full authority over
            all operational and technical decisions relating to the manufacture
            of Macugen(TM) at Raylo's facility.

      -     Eyetech will assign a sufficient number of its own employees, not to
            exceed 8, (the "Eyetech Staff") to work on the Macugen(TM)
            production on-site at Raylo's facility at Eyetech's sole cost.

      -     Raylo shall take all reasonable steps to facilitate Eyetech's
            decision-making regarding the Macugen(TM) production.

      -     Raylo shall direct its supervisors to follow all reasonable
            instructions concerning the Macugen(TM) production issued by the
            Eyetech Staff designated to oversee such production.

      -     Raylo shall direct its shift supervisors to report all technical
            problems related to the Macugen(TM) production to the Eyetech Staff
            as well as keeping Raylo management informed.

      -     Raylo will maintain full responsibility for cGMP compliance, safety
            and all administrative matters, including batch records and other
            production documentation related to the production of Macugen(TM).

      -     Eyetech will assist Raylo in establishing the inventory control and
            raw material tracking system for the Macugen(TM) production unit,
            but Raylo will be responsible for the implementation of such system.

      -     Eyetech will execute a confidentiality agreement covering all its
            employees which will prohibit the disclosure of any information
            obtained by Eyetech or its employees concerning proprietary
            information belonging to Raylo and/or Raylo's customers.

      -     Eyetech shall have the right to designate staff that will have
            access at all times to the Macugen(TM) production area and the
            office area assigned to Eyetech.

      -     A joint committee consisting of 2 Raylo and 2 Eyetech personnel will
            be established to handle HR, scheduling and other non-process
            related issues as they arise; this committee will meet weekly.

2.    Dedication of Production Areas and Raylo Support at Raylo's Facility

      -     Eyetech will pay Raylo for all Macugen(TM) batches manufactured at
            its facility, including rejected batches for the term of this
            agreement. Payment will be made as follows:

      -     Monthly rate of $[**] US, invoiced in Canadian dollars at an
            exchange rate to be agreed between Raylo and Eyetech

            - This rate covers resources equivalent to what have been employed
            to date on this project, and changes in scope (i.e. additional
            staff) will have to be negotiated independently
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            - This rate will be fixed for the first six months of the project,
            starting September 1, 2003. If the current plan (i.e. Eyetech
            operational control) is to be extended at this point, the rate will
            be reviewed and revised if necessary

            - Variable charges (non-key raw materials and consumables)
            associated with manufacturing will be charged separately, and are
            expected to be approximately $[**] US per batch. This figure can be
            confirmed and reviewed as necessary.

            - In terms of batch 8P, which will not be progressed, it is proposed
            that Raylo invoice Eyetech for $[**] US for this batch, with the
            understanding that there will be no reimbursement for Eyetech
            supplied raw materials that were utilized in this run.

      -     In exchange for the considerations given above no later than by
            September 5, 2003 Raylo will dedicate exclusively to Macugen(TM)
            production, and give Eyetech Staff full access to the following
            production areas:

                  1.    One Synthesis Suite

                  2.    One Purification Suite

                  3.    One Lyophilization Suite

      -     Eyetech will have certain process equipment dedicated to Macugen and
            will be used solely for Macugen production.

      -     Eyetech will be responsible for maintenance of an inventory of spare
            parts and any upgrades for equipment used in the production of
            Macugen(TM).

3.    Quality Control

      -     Operators will be trained to run the in-process Macugen(TM) assays.
            Additional equipment to perform the in-process Macugen (TM) assays
            may be purchased and installed at Eyetech's expense, if agreed by
            Raylo and Eyetech

4.    Quality Assurance

      -     Eyetech Staff will assume responsibility for streamlining batch
            records including review of batch records and "clean up" of the
            batch record process.

      -     Eyetech will make recommendations to Raylo as to new
            systems/processes and will work with Raylo to see if they can be
            implemented in Raylo systems.

      -     Raylo personnel shall provide QA oversight, batch record review, and
            Macugen related documentation to Eyetech upon Eyetech's request.

Neither Party shall make any press release or other public presentation or
disclosure with respect to this LOU nor the transactions contemplated hereby
without the prior written consent and approval of the other Party, except to the
extent required under applicable law or regulation or under the rules of any
stock exchange or NASDAQ.
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If the foregoing terms are acceptable, please sign both originals of this LOU
below, return to us one fully-signed original to acknowledge your agreement to
and acceptance of this LOU, and retain one fully-signed original for your files.

We look forward to the execution of this LOU and the continuation of our
relationship with regard to Macugen(TM).

                                    Very truly yours,

                                    EYETECH PHARMACEUTICALS, INC.


                                    By: /s/ Chuck Williams
                                        ---------------------------------
                                         Name:  Chuck Williams
                                         Title:  Senior VP, Manufacturing


ACCEPTED AND AGREED:

RAYLO CHECMICALS, INC.


By:   /s/Robin H. Nicol
      ------------------
      Name:  Robin H. Nicol
      Title:  Manager, Research, Development and Oligo Unit
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                    ADDENDUM TO LOU DATED AS OF SEPTEMBER 1, 2003

Raylo Chemicals, Inc ("Raylo") and Eyetech Pharmaceuticals, Inc. ("Eyetech")
hereby agree to add the provisions set forth below to their Letter of
Understanding effective dated as of September 1, 2003 (the "LOU"). This Addendum
shall be effective as of November 1, 2003.

      1.    Additional Space

In addition to the exclusively dedicated production areas at the Raylo listed in
the LOU Clause 2., Raylo will dedicate exclusively to the Macugen(TM) production
for a period not to exceed 180 days the following production areas:

            1.    One Synthesis Suite

            2.    One Purification Suite

            3.    One Area currently used for Glass Washing

      2.    Additional Payment

In addition to the monthly rate payable by Eyetech to Raylo, Eyetech shall pay
to Raylo for the Additional Space listed under clause 1 of this Addendum $ [**]
CDN per month.

      3.    Currency Rate

For the monthly payments of the $ [**]US under the LOU, which as of the
Effective date of this addendum will be paid in the amount of $ [**]CDN. For any
other payments denominated in US. Dollars it is agreed that Eyetech will pay
Raylo, at Raylo's option, in US. Dollars or at the exchange rate reported in the
Wall Street Journal Eastern Edition on the date the payment becomes due.

      4.    Outstanding Payments

An outstanding amount of $ [**]US invoiced to Eyetech by Raylo shall be paid to
Raylo before the end of calendar year 2003.

      5.    Renewal Option

Eyetech shall have the option to renew the LOU for an additional term of 180
days, but not beyond completion of the process validation.

                  [SIGNATURE NEXT PAGE]
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Accepted by:                                     Accepted by:

Raylo Chemicals, Inc.                            Eyetech Pharmaceuticals, Inc.

/s/ T. Matthew Colomb                            /s/ Paul G. Chaney
---------------------------------                -------------------------------
Signature                                        Signature

T. Matthew Colomb                                Paul G. Chaney
---------------------------------                -------------------------------
Printed Name                                     Printed Name

President                                        C.O.O.
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Title                                            Title