Pronuclei of fertilized oocytes were injected with the bacterial artificial chromosome (BAC) bWap-SEAP, containing 24 kb of the mouse whey acidic protein gene driving expression of a secreted form of human placental alkaline phosphatase lacking the membrane anchoring domain (SEAP, ClonTech), which serves as a promoter/enhancer reporter. Mice of founder line b6733 carry two copies of the transgene. Mammary glands of these mice express SEAP at a level of 5.1 ug/ml of milk; some ectopic expression is detected in liver and brain. (J:82809)