The objective of the project is to determine if cells other than early embryo cells can clone the mammalian blastocyst and participate in embryo development. The mouse will be used as the experimental animal. Cells for transfer will be obtained from late stage embryos, normal adult tissues, and neoplastic tissue. The effect on the cells and blastocysts will be determined by (1) recording microscopic changes in the transferred and blastocyst cells during in vitro development of the blastocyst, (2) following autoradiographically the fate of the cells in the embryo, and (3) placing the recipient blastocysts into foster mothers and studying the offspring for signs of an effect from the transferred cells. BIBLIOGRAPHIC REFERENCE: Brinster, R. L., Participation of teratocarcinoma cells in mouse embryo development. Cancer Research 36, 3412-3414, 1976.