We conducted a retrospective study to evaluate the outcome of 94 consecutive patients with high-risk hematological malignancies who received allo-PBSCT, following idarubicin (IDA)-intensified BUCY2 (IDA-BUCY2) myeloablative conditioning regimens (n=53) and BUCY2 conditioning regimens (n=41). IDA 15 mg/m(2) once daily was administered by continuous infusion on days -11 to -9, followed by BU, 3.2 mg/kg in divided doses daily, on days -6 to -4, and i.v. injection of CY, 1.8 g/m(2) once daily on days -3 to -2 in the IDA-BUCY2 group. The relapse rate in patients in the IDA-BUCY2 and BUCY2-conditioning regimens group was 18.9 and 39%, respectively (P=0.030). There was no significant difference in terms of TRM. The cumulative probabilities of OS and disease-free survival at 2 years for patients conditioned with the IDA-BUCY2 and BUCY2 regimens were 65.3% vs 46.8% (P=0.038), and 63.5% vs 43.4% (P=0.025), respectively. Multivariate analysis showed that IDA-BUCY2 regimens and limited chronic GVHD were the only two factors resulting in improved survival and reduced relapse rate. This retrospective study suggests that IDA-intensified BUCY2 may be substituted for BUCY2 as conditioning regimen for patients with high-risk hematological malignancies.