Short-term growth of human leukemic cells from patients was made possible by the development of a special conditioned medium. This method is presently being used to determine specific anti-leukemic therapy for individual patients based on culture results. It is essential to isolate and characterize those growth factors present in the special conditioned medium. One or more of these factors will permit cloning of leukemic cells from patients with a high cloning efficiency (60-100 percent). This system has the potential to provide optimal material for a variety of biochemical and immunological studies relevant to the management of leukemic patients. It is generally accepted that single anti-cancer agents are rarely curative in widely disseminated human cancer. Consequently, the rational use of drug combinations will be studied using murine and human leukemic cells in culture. Drug Development studies for anti-cancer agents is initiated by chemists who will provide compounds of novel design. These compounds will be evaluated in a cell culture system and preliminary work concerning molecular sites of action investigated. The active new compounds will then be evaluated in murine transplantable tumor systems with survival, pharmacology and toxicology studies. Additional animal studies involving other species will then be carried out. Promising anti-tumor compounds after the above studies will then be evaluated in Phase I Clinical Pharmacology and Drug Metabolism and Phase II Clinical Activity in Patients with neoplastic diseases.