Eighty-five adult patients under the age of 50 years with acute myeloid leukaemia (AML) were entered into a prospective controlled study conducted to compare the effectiveness of allogeneic or autologous bone marrow transplantation and intensive chemotherapy for patients in first complete remission. Sixty-one patients (72%) achieved complete remission then received a consolidation treatment. After consolidation, 58 patients who were still in remission were assigned to three different therapeutic modalities. Fifty-two patients were evaluable: 20 patients who had an HLA-identical sibling donor underwent allogeneic bone marrow transplantation within 3 months after achievement of complete remission; the other 32 patients were randomized to receive autologous bone marrow transplantation or intensive sequential chemotherapy. The actuarial risk of relapse at 3 years was 18% for the allogeneic patients, 50% for the autologous patients and 83% in the chemotherapy group. The difference was highly significant (P less than 0.0002). The disease-free survival was respectively 66% (95% confidence interval 41-85%), 41% (95% confidence interval 16-66%) and 16% (95% confidence interval 0-31%) (P less than 0.004). We conclude that allogeneic bone marrow transplantation is presently the best therapeutic approach for patients with AML in first complete remission.