This project concerns the study of the relationships between those cells of the hemopoietic system of rats and mice that can be induced into the erythroid series by erythropoietin, those that can be induced into the granuloid series by "colony stimulating factor", and pluripotent stem cells. We are studying possible competitive effects of the two inducers on the other pathway of differentiation and the effects on the number of pluripotent stem cells. We are also working on the in vitro reconstruction of the splenic microenvironment that plays a large role in the induction of erythropoiesis. BIBLIOGRAPHIC REFERENCES: Van Zant, G.E., Goldwasser, E. and Baron, J.M. Study of Haemopoietic Microenvironment in vitro. Nature 260, 609-611 (1976). Van Zant, G.E. and Goldwasser, E. The Effects of Erythropoietin in vitro on Spleen Colony-Forming Cells. J. Cell Physiol. 90,241-252 (1977).