Modulation and control of blast cell proliferation in acute myelogenous leukemia (AML) by humoral agents is being examined. In addition, effects of humoral agents on differentiation of blast cells will be assessed. Blast cell proliferation will be studied using blast colony-forming assays (blast CFC) and 3H-TdR incorporation in liquid culture. Target populations will include leukemia cell lines derived from patients with myeloid leukemias, and peripheral blood and bone marrow from patients with AML. Cell cycle status of blast CFC will be studied by thymidine suicide and cell cycle status of other populations by flow microfluorometry. Differentiation will be assessed by loss of self-renewal capacity of blast CFC, histochemistry, phagocytosis and monoclonal antibodies to cell surface antigens. The actions of the following humoral agents will be examined: (1)\prostaglandins, (2)\cyclic nucleotides, (3)\steroid hormones, (4)\colony-stimulating factor (CSF), (5)\media conditioned by PHA-stimulated mononuclear cells, (6)\erythropoietin and (7)\media conditioned by leukemia cell lines. The latter appears to contain growth factors for blast cells which we will characterize during these studies. Multiple sources of CSF will be studied and the action of these materials contrasted to that of PHA-LCM. The actions of the CSF preparations and leukemia CM on leukemia blasts will be contrasted to effects on normal granulocyte macrophage progenitors. These studies represent a continuing series of investigations in humoral control of normal and abnormal myeloid cell proliferation.