More than 20,000 patients have survived 5 or more years after allogeneic transplantation, and the number of allogeneic transplantations performed each year continues to increase rapidly. The indications for allogeneic bone marrow transplantation are beginning to change as research continues on the use of transplantation to treat genetic diseases. This article focuses on the use of allogeneic bone marrow transplantation for the treatment of hematologic malignancies, including acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphoblastic leukemia, myelodysplastic syndrome, and chronic lymphocytic leukemia.