The production and profit impacts of recombinant Bovine Somatotropin (rbST) on select New York dairy farms were estimated using data over the years 1994 through 2004, by comparing matching farms which use and do not use rbST. The use of rbST increases milk production per cow and decreases the cost of production per hundredweight of milk. The cost penalty (cost reduction) is $0.39 per hundredweight for those currently using rbST to stop using rbST, while the average treatment effect is $0.73.