Biochemical and Dynamic change of mammary glands in different reproductive states were studied in comparison with histological structures in female and male transgenic mice bearing human transforming growth factor alpha (TGF alpha) cDNA under the control of the mouse mammary tumour virus enhancer/promoter. Female and male F1 mice between SHN female and transgenic male mice were divided into TGF alpha (+) and TGF alpha (-) groups according to the presence of TGF alpha gene at approximately 50 days of age. While there was little difference in mammary gland contents of DNA and RNA in females at 2 months of age, both nucleic acid contents were elevated markedly in TGF alpha (+) female mice with large variations at 4 months. These extremely high DNA and RNA contents in the TGF alpha (+) group declined to the level of the TGF alpha (-) group in the middle of pregnancy and at the end of pregnancy, respectively. Thymidine kinase (TK) activity in the mammary glands as an index of DNA synthesis was significantly higher in TGF alpha (+) mice than in TGF alpha (-) mice at both 2 and 4 months of age and the high TK in TGF alpha (+) mice also declined to the level of TGF alpha (-) mice with pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)