Exclusive Patent License Agreement

                                                                   

Exhibit 10.4

                                  
ZYMOGENETICS

                                
October 17, 2005

VIA FAX (615 844 1281) AND FEDERAL EXPRESS

Dr. Samuel Lynch

President and CEO

BioMimetic Therapeutics, Inc.

389-A Nichol Mill Lane

Franklin, TN 37067

Dear Dr. Lynch:

          
I am writing to summarize the recent discussions between you and
Dr.

Bruce Carter. ZGEN and BMTI desire to clarify Sublicense Fees
payable by BMTI to

ZGEN under their Exclusive Patent License Agreement dated March 28,
2001 (the

"2001 License Agreement") with regard to the 2003 sublicense
granted by BMTI to

Luitpold, in accordance with the terms described below.

          
With regard to the Exclusive Sublicense Agreement and Research,

Development and Marketing Agreement, both dated December 9, 2003,
between BMTI

and Luitpold Pharmaceuticals, Inc. (the "Luitpold Transaction"),
ZGEN and BMTI

agree that the total amount of Sublicense Fees payable by BMTI to
ZGEN under

Section 4.7 of the 2001 License Agreement shall be **, payable
within ten (10)

days after first