From October 1987 to December 1990, 101 patients with acute myeloid leukemia (AML) were randomized to be transplanted in first complete remission (CR1). Preparative regimen including Cytoxan (120 mg/kg) with total body irradiation (CYTBI) (N = 50) or busulfan (16 mg/kg) (BUSCY) (N = 51) was followed by allogeneic bone marrow transplantation (BMT) from an HLA-identical sibling. Mean time between diagnosis and BMT was 119 days. The outcome for CYTBI at 2 years is better for probability of disease-free survival (DFS) (72% v 47%) (P less than .01), survival (75% v 51%) (P less than .02), relapse (14% v 34%) (P less than .04), and transplant mortality (8% v 27%) (P less than .06). In multivariable analysis, higher relapse and decreased survival and DFS were associated with BUSCY regimen, while chronic graft-versus-host disease also influenced independently the probability of relapse. This demonstrates the present limitation of busulfan use in this setting, possibly due to probable individual variations in biodisponibility. Furthermore, besides the anti-leukemic effect of preparative regimens, this trial points out the progress accomplished in BMT management (transplant mortality = 8% in CYTBI) over the last 20 years as well as the effectiveness of transplant in early first CR after CYTBI (DFS = 72% at 2 years).