In an effort to reduce the relapse rate after unpurged autologous bone marrow transplantation (ABMT) in patients with acute myeloid leukemia (AML) in first complete remission (CR1), the standard conditioning regimens (cyclophosphamide/busulphan and cyclophosphamide/TBI) were intensified by adding idarubicin. Seventeen patients received a continuous infusion of 21 mg idarubicin/m2/day for 2 consecutive days in addition to the standard preparative regimen. Thirteen patients served as a historical control group. The 2-year disease-free survival (DFS) of 82% in the study group was significantly (P = 0.047) better compared to 46% DFS in the control group. The relapse rate (RR) was also significantly lower (7% vs 45%; P = 0.035) in the study group. The median time to reach a white cell count (WCC) of 0.5 x 10(9)/l was 20 days in the study group vs 17 days (P = NS) in the control group. The median time until recovery of the platelet counts to 20 x 10(9)/l was 152 days in the study group vs 57 days (P = NS) in the control group. The hypoplasia in the study group resulted in a trend towards a higher need for transfusions: a median number of 38 units of erythrocytes vs 23 units in the control group (P = NS) and 23 units of platelet vs 18 units in the control group (P = NS). This pilot study suggests that addition of idarubicin to the standard conditioning regimens may improve DFS and overall survival (OS) of patients with AML treated with ABMT in CR1. These results should be confirmed in a prospective randomized study.