The problem of projecting future use patterns of agricultural biotechnology products in order to evaluate their potential for development and commercialization is a challenging proposition for economists. While many have attempted ex ante methods of projecting adoption and diffusion rates, very few have tested their ex ante results after the fact. In this paper, we use the results of a continuous survey of California dairy producers ex post to test the predictions of an ex ante study of adoption of recombinant bovine Somatotropin (rbST) carried out using data 4-7 years prior to the availability of the new technology.