Conduct virological investigations to propagate sufficient quantities of hyperplastic alveolar nodules (HAN) tissues (or outgrowth lines) in selected MTV positive and MTV negative BALB/c and other mouse strains by traditional in vivo serial transplantation procedures. It is expected that some HAN tissues will be made available to NCI for other testing. Detect and quantitate levels of MuMTV expression as proteins, nucleic acid, and complete virion in HAN tissues of varying tumorigenicities in the selected mouse strains, using standard or newly developed biochemical and immunological methods (e.g., nucleic acid hybridization, immunoperoxidase techniques - EM). Alter virus expression in HAN tissues with immunologic reagents, chemicals, and/or hormones in efforts to define regulatory controls which may determine functions of viral components during mammary tumorigenesis. Apply developed technology and reagents in the mouse model for the detection of oncornavirus expression in human mammary tissues and tumors.