In this study, we utilized a conditioning regimen with fludarabine and myeloablative dose i.v. BU (12.8 mg/kg) (FluBU) in 36 adult patients (median age: 44 years, range: 18-61) with myeloid or lymphoid malignancies at standard risk (n=10) or high risk of relapse (n=26), who received an allogeneic hematopoietic SCT (HSCT) from HLA-matched related (n=16) or unrelated (n=20) donors. The source of hematopoietic stem cells was peripheral blood in 28 and marrow in 8 cases. Rabbit-antithymocyte globulin at 7 mg/kg was utilized in 21 patients. Acute GVHD grade II-IV was observed in 19% of the patients (grade III-IV in 14% of patients) and chronic GVHD in 11 of 30 evaluable patients (37%). At median follow-up of 737 days (range: 152-1,737) for alive patients, overall survival rates in standard- and high-risk patients were 80 and 35%, respectively, and event-free survival rates were 70 and 31%, respectively. TRM was 10% in standard-risk and 19% in high-risk patients. Post transplant relapse was observed in 20% standard-risk and in 46% high-risk patients. FluBU conditioning regimen is associated with a limited hematologic and extrahematologic toxicity and with an antitumor activity comparable to other standard myeloablative regimens.