The pBC1 vector is a 21.6 kb vector designed to facilitate expression of recombinant proteins in the milk of transgenic animals. The pBC1 Milk Expression Vector Kit is intended for use in performing feasibility studies in mice, with the expectation that the user is interested in eventual large scale recombinant protein production using larger animals. Successful expression of recombinant protein in transgenic mice has generally been indicative of successful expression in larger animals such as goats or cows (Young et al., 1997). For feasibility studies, transgenic mice provide the added advantage of shorter generation times and faster evaluation than larger herd animals.