FIRST AMENDMENT TO STOCK PURCHASE AGREEMENT

Exhibit 10.16

FIRST AMENDMENT TO

STOCK PURCHASE AGREEMENT

FIRST AMENDMENT TO STOCK PURCHASE AGREEMENT dated as of September 28, 2006 by and between Zila, Inc, a Delaware corporation (“Seller”) and NBTY, Inc., a Delaware corporation (“Buyer”).

W I T N E S S E T H:

WHEREAS, the above parties have entered into a Stock Purchase Agreement dated as of August 13, 2006 (“Stock Purchase Agreement”); and

WHEREAS, the Stock Purchase Agreement provides in Section 7.10 that it may be amended by the written agreement of the Buyer and Seller; and

WHEREAS, the undersigned parties wish to amend the Stock Purchase Agreement in the manner set forth below;

NOW, THEREFORE, the undersigned parties agree as follows:

1. The last sentence of paragraph 25 (c)(ii) of Exhibit B is hereby amended by deleting it in its entirety and replacing it with t