The influence of specific hormones upon human erythroid differentiation, proliferation and maturation will be examined in relation to known regulatory factors. A serum-free system for the culture of human erythroid progenitors will be employed to develop a hormone-depleted plasma clot culture technique for assaying human erythroid colony formation in the presence and absence of precisely known quantities of specific hormones. These techniques will permit the identification, isolation, characterization and comparison of target cell populations within heterogenous mononuclear cells derived from healthy adults and anemic patients, using velocity sedimentation analysis, thymidine suicide studies and detailed time-course investigations. Comparison of hormone-induced responses will be made between peripheral blood and bone marrow mononuclear subpopulations obtaned from normal adults and patients with endocrinopathies. Hormonal modulation of cell-to-cell interactions between T-cells, B-cells, null-cells, monocytes and/or responsor cells, and between these subpopulations and lymphocytes of anemic patients with leukemia, lymphoma and immunologic disorders will be investigated. These in vitro techniques will be applied to the study of patients with refractory hypoproliferative anemias and their relevance to clinical responsiveness to hormonal agents of the same class will be determined. The mechanisms by which hormones alter human erythropoiesis in normal and abnormal hematologic states will be studied with reference to cell surface recognition processes. In addition, hormonal effects on the production and activity of lymphocyte conditioned media will be examined. These methods may provide a model system for the study of the hormonal mechanisms that control cellular processes.