1.48 kb of the mouse mammary tumor virus (MMTV) long terminal repeat drives mammary epithelium-specific expression of cre. The cre expression cassette is followed by several introns of methallothionein-I (MT-I) and its polyadenylation sequence. Five lines (104A, 105, 106, 107, and 108) were generated. Cre expression in line 105 is restricted to the mammary gland. (J:165292)