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                                                                   Exhibit 10.21

                                December 22, 2003

Ms. Elizabeth A. O'Dell
53 Avon Drive
Essex Fells, New Jersey

Dear Liz:

This letter will confirm certain matters related to your employment by Alteon
Inc. (the "Company") and shall constitute an amendment to your Employment
Agreement with the Company dated as of October 21, 2000 (the "Employment
Agreement").

Your Term of Employment, as defined in Paragraph 1 of your Employment Agreement,
is due to expire on December 31, 2003. The Term of Employment shall now be
extended for an additional three years to December 31, 2006.

In connection with this amendment, the Company shall issue and deliver to you
options to purchase 100,000 shares of the Company's common stock at an exercise
price of $1.56 per share, which is the fair market value of the stock on
December 10, 2003 when the Compensation Committee of the Board approved this
award. The options will vest in 36 equal monthly installments and will be
subject to the terms of the Company's Amended 1995 Stock Option Plan.

Paragraph 3 of your Employment Agreement ("Compensation") is amended to indicate
that your base salary for calendar year 2004 shall be at the rate of $183,872
per annum and that the amount of annual cash bonus you will be eligible to
receive at the end of each year of the extended term shall be $20,000.

Paragraph 4 of your Employment Agreement ("Other Benefits") is amended by adding
the following new subparagraph C at the end thereof:

         C.       Upon a Change in Control (as defined in the Alteon Inc. Change
in Control Severance Benefits Plan, effective as of February 27, 1996 (the
"Plan")), you will be entitled to all of the benefits to which you would be
entitled under the Plan as in effect on the date hereof if a Change in Control
occurred on the date hereof, notwithstanding any amendment or termination of the
Plan or other action by the Board of Directors of the Company as permitted under
the Plan which may affect your entitlement to benefits thereunder after the date
hereof.

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Elizabeth O'Dell                                               December 22, 2003
Letter Agreement                                                          Page 2

Paragraph 12 of your Employment Agreement ("Termination Without Cause") is
amended to replace the second sentence thereof with the following:

         "In the event (a) the Company elects to terminate this Agreement prior
         to the end of the Term of Employment, or (b) the Company gives Employee
         notice of its election not to extend the Term of Employment beyond the
         expiration of the then current Term of Employment, or (c) by the date
         which is four months prior to the end of the then current Term of
         Employment, the Company has not offered to extend the then current Term
         of Employment, the Company shall continue to pay the Employee the full
         Salary (exclusive of bonuses, if any) as such Salary would have
         otherwise accrued, plus medical/health benefits, including life
         insurance, for a period of 12 months after the effective date of
         termination."

Paragraph 20 of your Employment Agreement ("General") is amended to include this
letter as part of the "entire agreement," with respect to the subject matter of
your employment by the Company. Except as modified by this letter, the terms of
your Employment Agreement shall remain in full force and effect.

If the foregoing is acceptable to you, please indicate your agreement by signing
and returning the enclosed copy of this letter.

                                           Sincerely,

                                           /s/ Kenneth I. Moch
                                           -------------------------------------
                                           President and Chief Executive Officer

Enclosure

Accepted and agreed this
22nd day of December 2003

/s/ Elizabeth A. O'Dell
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Elizabeth A. O'Dell