The objectives of this proposal are to study the factors controlling hematopoiesis in normal man and patients with malignant hematologic diseases. Specific objectives are (1) the purification and characterization of colony-stimulating activity to determine whether it is or is not a physiologic regulator of granulopoiesis, or merely a factor required for in vitro growth of myeloid stem cells; and (2) the critical examination of substances derived from mature granulocytes which are purported to have feedback regulatory activity (so-called "chalones").