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                                                                   EXHIBIT 10.20

[GELTEX PHARMACEUTICALS, INC. LOGO]





November 17, 1997




Edmund J. Sybertz, Ph.D.
RD 2 10 Ryan Court
Chester, NJ  07930

Dear Ted:

It is my pleasure to extend to you an offer of employment with GelTex
Pharmaceuticals, Inc. We would like you to join us in February 1998, as Senior
Vice President, Research and Development. Your bi-weekly rate of pay will be
$7,692.31, which is the equivalent of an annual rate of $200,000, based on a
40-hour workweek. After you have been employed for one year, and annually
thereafter, you will be eligible for a performance and salary review on or near
your anniversary date.

You will be eligible for a bonus opportunity equal to 30% or more of your base
salary on an annual basis subject to the approval of the Board of Directors of
GelTex. In the event that GelTex terminates your employment without cause, you
will be eligible to receive six months of severance pay, which will be equal to
six months of your base salary.

In addition, we will grant you an option to purchase 110,000 shares of GelTex
common stock at the closing price on the day your employment begins. Ten
thousand shares will vest immediately, with the remaining shares vesting over a
four year period at the rate of 1/48 per month of service from the date of the
option grant. GelTex believes that ownership of common stock is the best way to
significantly motivate and reward long term contributions to the company.

GelTex will pay the usual and customary closing costs of your existing home in
New Jersey and on a new home in the Boston area. If necessary, the company will
make available a "bridge loan" to provide for the down payment and associated
purchase costs of your new home. The terms of the loan will be determined at a
later date. If selling your home becomes a problem, we will discuss suitable
arrangements to allow you to sell your home. GelTex will also pay the costs
associated with moving your household goods to this area and up to six months
temporary living expenses.


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In addition, you will be eligible for the company benefits described below:

         - Three weeks paid vacation per year, increasing to four weeks after
           five years of employment.

         - Eleven paid holidays, including a floating holiday that may be taken
           at your discretion.

         - Company paid term life insurance equal to two times your annual
           salary.

         - Long-term disability insurance which provides up to 60% of your
           monthly salary.

         - Group health insurance through The Guardian. The company pays 75% of
           the premium for family or individual coverage.

         - Group dental insurance through the Delta Dental Plan. The company
           pays 75% of the premium for family or individual coverage.

         - Participation in the GelTex Pharmaceuticals 401(k) Plan. Each
           employee may contribute up to 15% of gross pay (subject to an IRS
           maximum) which will then be excluded from the employee's taxable
           income.

         - Participation in the GelTex Pharmaceuticals Employee Stock Purchase
           Plan. The purpose of the plan is to provide employees an opportunity
           to purchase shares of common stock of the company.

         - Tuition assistance of up to $3,000 per year for relevant academic
           courses.

         - Participation in the GelTex Pharmaceuticals Flexible Benefits Plan
           which allows you to fund for eligible dependent care expenses on a
           pre-tax basis.

While the foregoing represents the current benefits, they are continuously being
reviewed and are subject to modification. Also, the above is a summary of the
benefits. Complete descriptions are contained in the appropriate plan documents
or other company documents, and will be discussed in detail with


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Dr. Sybertz
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you during your first few days of employment. This letter constitutes the entire
understanding of the terms of your employment and supersedes any prior written
or oral statements. In addition, nothing herein shall be construed as, or
interpreted to constitute, the terms of a contract of employment for either a
definite or indefinite time.

Your employment with GelTex Pharmaceuticals will be conditional upon documents
establishing that you are authorized to work for GelTex Pharmaceuticals pursuant
to the Immigration Reform and Control Act of 1986. These documents must be
provided to the company within your first three days of employment. You will
also have to complete certain other standard company forms and documents.

If accepted and agreed upon, please sign both copies of the offer letter,
retaining one copy for your files and returning the other to GelTex
Pharmaceuticals.

Ted, all of us at GelTex are most impressed by you. We are convinced that you
could make key contributions to the success and growth of our company. We think
that GelTex will be a very exciting place to work over the next few years and we
would like you to join us in that excitement.

Sincerely,



/s/ Mark Skaletsky

Mark Skaletsky
President and CEO


Accepted by:


/s/ Edmund J. Sybertz, Ph.D.
----------------------------
Edmund J. Sybertz, Ph.D.

Date: January 19, 1997