In this pilot study; we assessed the immunosuppressive and the antileukemic potential of a combination of busulfan and melphalan prior to allogeneic BMT in 25 adult patients with refractory or relapsed hematological malignancies. Twelve patients were transplanted for acute myeloid leukemia (relapse: five patients; primary refractory: four patients; second remission: two patients), two patients for primary refractory acute lymphoblastic leukemia, nine patients for chronic myelogenous leukemia (accelerated phase: six patients; blastic phase: three patients) and two patients for primary refractory lymphoma. All received an unmanipulated marrow from HLA-identical siblings. All patients but one engrafted (median time to ANC > or = 0.5 x 10(9)/l = 17 days, to platelets > or = 50 x 10(9)/l = 29 days). Full chimerism was documented in the seven evaluable patients. The probability for developing acute GVHD was 58%. Complete remission was obtained in 17/18 measurable patients. With a 42 month median follow-up, eight patients are alive in unmaintained remission. The 4-year probabilities for relapse, survival, and DFS are respectively: 42%, 35%, and 31%. These results show that the combination of busulfan and melphalan ensures an effective immunosuppression allowing long-term engraftment. This regimen can provide long-term disease-free survival in patients with high-risk disease and thus represents an interesting alternative to the CY and/or TBI-containing regimens.