Bone marrow transplantation was initially introduced as a treatment modality for patients with acute leukemia who had failed all conventional treatment. When viewed within this context even the early results of bone marrow transplantation were encouraging. When transplantation was performed on patients with acute leukemia in first remission results clearly superior to the best currently obtainable with chemotherapy were documented. In this group of patients leukemic relapse is relatively unusual. Yet, some 40% of patients succumb, chiefly to graft-versus-host disease (GVHD). Current research efforts are aimed at blunting GVHD. They include the removal of T-lymphocytes from the transfused marrow by treatment with lectins and with antibodies. New immunosuppressive drugs may also prove helpful in improving the results obtained with bone marrow transplantation.