Contract

EXHIBIT 10.52

[ * ] = Certain confidential information contained in this document, marked by brackets, has been omitted and filed separately with the Securities And Exchange Commission pursuant to Rule 24b-2 of the Securities Exchange Act of 1934, as amended.

November 30, 2005

Xxxxx Xxxxxxx, Ph.D.

Cystic Fibrosis Foundation Therapeutics, Inc.

0000 Xxxxxxxxx Xxxx

Xxxxxxxx, XX 00000

Dear Xx. Xxxxxxx:

The purpose of this letter (“Letter”) is to amend the Study Funding Agreement, between the undersigned parties, dated June 17, 2003, as amended (the “Agreement”). By signing below, the undersigned parties agree to the following:

In Section 8.1(c) of the Agreement, [ * ] shall be replaced with [ * ].

All other terms and provisions of the Agreement shall remain unchanged and are in full force and effect.

XXXXXX-XXXX PHARMACEUTICALS, INC.
By:		/s/    XXXX X. XXXXXXX				Date: December 13, 2005
		Xxxx X. Xxxxxxx Vice President, General Counsel

Agreed to and Acknowledged by:

CYSTIC FIBROSIS FOUNDATION THERAPEUTICS, INC.
By:		/s/    XXXXXX X. XXXXX				Date: December 9, 2005
		Xxxxxx X. Xxxxx, Ph.D. President and CEO