BACKGROUND: We assessed the toxicity and feasibility of the three-alkylator combinations as conditioning regimens for allogeneic hemopoietic stem cell transplantation (HSCT) in 23 adult patients with acute leukemia. METHODS: Sixteen patients were transplanted for acute myeloid leukemia, six for acute lymphoblastic leukemia, and one for myelodysplastic syndrome. Group A included thirteen cases of relapsed refractory, 2 relapsed after first HSCT and group B eight patients in first complete remission or two in second complete remission. Eleven cases received G-CSF mobilized CD34+allogeneic peripheral blood stem cells (PBSCs) in addition to bone marrow (BM) and three in vivo expanded BM by G-CSF and eight unmanipulated BM and one from syngeneic BM after conditioned with busulfan, thiotepa and melphalan (n=14) or cyclophosphamide, thiotepa and melphalan (n=6) or TBI, melphalan and thiotepa (n=3). RESULTS: Twelve of thirteen patients in group A patients engrafted successfully and only one patient failed to achieve complete remission (CR). All patients in group B had successful engraftment. The median days reaching absolute neutrophil count (ANC) more than 500/microliter and platelet more than 30,000/microliter in group A and group B were 13.4 days (7-22), 17.9 days (9-40) and 16.3 days (10-21), 22.6 days (13-38), respectively. Acute graft vs host disease (GVHD) developed in both groups with the incidence of seven (78%) for group A and six (60%) for group B. The major regimen-related toxicity was mucositis with incidence of 95.7% (22/23). The disease free survival rate after HSCT with median follow-up of 161 days (31-283 days) and 101 days (22-163 days) in each group were 24% and 62.5%, respectively. CONCLUSION: Although the observation period is limited, this study shows that the combination of triple-alkylating regimens are tolerable as a preparative regimen for allogeneic HSCT for both high-risk and standard-risk leukemic patients. We need to confirm effects of these regimens in prospective randomized-controlled studies in the future. (allo-BMSCT) and 14 cases of autologous peripheral blood stem cell transplantation (aPBSCT) were underwent. With a median follow-up of 293 days (range, 35~510), the relapse rate was 34.1% (14/41 cases) in chemotherapy-only group and 13.5% (5/37 cases) in transplant-group. The probability of disease-free survival (DFS) at 2 years of chemotherapy-only group, aPBSCT group, and allo-BMSCT group were 20.1%, 44.9%, and 90%, respectively. The relapse-probability at 2 years of three groups were 76.1%, 55.1% and 11.1% in order, respectively. Univariate analyses showed that age (P=0.0274) and augmentation with BHAC (p=0.0334) were significant factors for achieving CR.