This project is designed to determine the role of hormones and growth factors in the development and differentiation of normal mammary gland and in the development growth, and maintenance of mammary tumors. Studies include: 1) examining the roles of epidermal growth factor and mammary gland-derived growth factors in lobuloalveolar development of the mouse mammary gland; 2) defining the roles of estrogen and progesterone in priming the mammary tissue prior to whole organ culture to determine their effects on induction of EGF receptors, mammary glandderived growth factor receptors, and the production of growth factors by the animals; 3) examining the effect of sialadenectomy on mammary tumor incidence and growth in mice as well as the production of preneoplastic hyperplastic alveolar nodules; and 4) defining the hormone receptor and response status of the NOG-8 mouse mammary epithelial cell line.