Accumulated age and proliferative stress of the pluripotent hemopoietic stem cell compartment will be studied for its effect on x-ray/chemotherapeutic alkalating agent-induced acute granulocytic leukemia in vitro. RFM mice, a strain demonstrating a high incidence of acute myelogenous leukemia following exposure to total body irradiation and inbred Swiss mice (SIM), a strain with a very low incidence of leukemia will be studied. Serial transfer of bone marrow from normal mice to lethally irradiated recipients will be carried out to stress normal hemopoietic stem cells. Each generation and the initial group of mice will be exposed to a leukemogenic dose of total body irradiation or nitrogen mustard. Bone marrow from treated animals, 3 months after exposure to the cytotoxic agent, will be explanted to an in vitro culture system which has been demonstrated to generate continuous tissue culture lines of acute promyelocytic leukemia. Clonal derived APML cell lines will be characterized for the rapidity with which they are induced in marrow cultures. These studies should determine the effects of: genetic susceptibility to leukemia, accumulated proliferative stress on the stem cell compartment, and recent or delayed exposure to total body irradiation or alkylating agent cytotoxic therapy on the induction of acute myelogenous leukemia. We have demonstrated no spontaneous leukemia in over 400 SIM bone marrow cultures over the last 3 years. None of 36 cultures of RFM c/Na or RFM s/Na have spontaneously generated acute myelogenous leukemia. Studies of the effects of total body irradiation or nitrogen mustard on the first generation of bone marrow donors are in progress.