The project has two major objectives. The first is the application of the agar culture technique for detection of quantitative and qualitative defects in granulocytic stem cells (CFU-c) in the marrow of patients with leukemia and myeloproliferative disorders in both the untreated phase and during the course of therapy. This screening protocol is designed to provide detailed information of diagnostic and prognostic value. The second major objective evolves from this screening programme and is aimed at investigating (1) the nature of the cellular and regulatory lesions in leukemia; (2) the interaction between normal and leukemic hematopoietic cell populations during the development and treatment of the disease. BIBLIOGRAPHIC REFERENCES: Moore, M.A.S. Cellular interactions in normal and leukemic granulocytic differentiation. In: Proc. 11th Internat. Cancer Cong., Excerpta Medica, in press, 1977. Broxmeyer, H.E., Moore, M.A.S. and Ralph, P. Cell-free granulocyte colony inhibiting activity (CIA) derived from human polymorphonuclear leukocytes (PMN). Exp. Hematol., in press, 1977.