From December 1975 until October 1988 292 bone marrow transplantations (bmt) have been performed at the Center for Tumor Research and Tumor Therapy, University Hospital Essen; 251 of these transplantations were allogeneic, 30 autologous and 11 syngeneic. The main indications were ALL (n = 39), AML (n = 132), CML (n = 75) and severe aplastic anemia (n = 26). Now the transplantation rate is one bmt per week. Early transplantation during a controlled stage of disease provides the best chance of cure. Important prerequisites of a successful allotransplantation are patient age under 45-50 years, good general condition and a histocompatible donor. In case of autologous bmt, being mainly tested in acute leukemias and malignant lymphomas, the age limit is 50-55 years. If the allogeneic transplantation is performed during an early stage of disease, the cure expectancy is about 50% for acute leukemia in first remission and CML in chronic phase. In the case of severe aplastic anemia the cure rates are even higher, provided that the transplant is grafted before multiple blood transfusions have been given. In AML the risk of relapse after autologous bmt is higher than after allogeneic transplantation, but the preliminary data are promising. The question of whether or not autologous bmt is superior to conventional chemotherapy of AML, has to be investigated.