L1210 leukemia cells will be mixed with normal murine marrow cells and treated in vitro with deoxycoformycin in combination with Ara-A or with deoxyadenosine. These agents are cytotoxic in vitro for L1210 leukemia cells and for human leukemia cells and appear to be less toxic for hematologic stem cells. The treated marrows will be tested for their ability to reconstitute the hematologic systems of lethally irradiated mice. The long term survival of mice indicates survival of hematologic stem cells and effective purging of leukemic cells from marrow. Biochemical parameters through which deoxycoformycin exerts its cytotoxic effects will be monitored. The relevance of the biochemical sequelae of pharmacologic treatment to leukemia-free marrow engraftment will be evaluated. This is a promising model for purging marrow of leukemic cells. The application of this technique to human leukemia may make autologous bone marrow transplantation an effective treatment of leukemia.