The objective of this research program may be summarized under the following two headings: (1.) To study the nature of hormonal regulation of nucleic acids and protein synthesis during growth and differentiation of the mouse mammary gland. (2.) To study the interactions among the hormone regulated macromolecular events and the carcinogenic chemical and/or viruses during neoplastic transformation of the breast tissue. Mammary tissue from the animal and also organ cultures will be examined. Methods of cell fractionation, density gradient analyses, electrophoresis and column chromotography will be used for characterizing the various macromolecules. In vitro incubation systems will be utilized for determination of the enzyme and protein synthesizing activity and also the macromolecular activities of the subcellular fractions. Incorporation of radioactively labeled precursor compounds into the macromolecules determined by liquid scintillation spectrophotometry and autoradiography will be used as a measure of the rate of cellular biosynthesis. Attempts will be made to correlate the molecular events with cellular ultrastructures as determined by electronmicroscopy. Information obtained from these studies will be used for elucidation of the problems of hormone regulation differentiation and its bearing on the neoplastic disease.