The impact of bone marrow transplantation and chemotherapy on remission duration and survival in acute leukemia is controversial. Most studies on either procedure deal with selected patients and lack randomized or concurrent controls; many exclude high-risk subgroups. There are only a few preliminary reports on the direct comparison between bone marrow transplantation and intensive chemotherapy. Considerable controversy remains as to whether patients with AML in first remission who have an HLA identical sibling should receive a bone marrow transplant at that time or whether the transplant should be delayed until relapse or second remission. In patients under the age of 25 years, results of bone marrow transplantation are considered to be equivalent or superior to those achieved with chemotherapy. Because of a high lethality rate few results suggest that survival of patients transplanted during first remission is not superior to that obtained by intensified chemotherapy; however, the relapse incidence is decreased. In recent years, results in adult ALL, treated with various intensified programs, have improved considerably and are nearly comparable to those obtained in childhood ALL. Therefore, allogeneic bone marrow transplantation is usually performed in standard risk patients during second remission and, if relapse occurs within the first three years. It is not clear at present whether ALL high-risk patients will benefit from bone marrow transplantation during first remission.