We retrospectively analyzed data on 628 leukapheresis from 160 consecutive patients with hematologic or solid malignancies to identify predictive factors affecting the achievement of optimal peripheral blood progenitor cell (PBPC) collection, which was defined as > or = 5x10(6) CD34+ cells/kg. In univariate analysis, a diagnosis of multiple myeloma, no prior axial skeletal radiotherapy, absence of exposure to alkylating agents and cisplatin, fewer cycles of chemotherapy, and fewer number of previous chemotherapy regimens favored the achievement of target number of PBPC. In multivariate analysis, the absence of prior exposure to alkylating agents, especially cyclophosphamide, (P=0.003, RR=2.08) and cisplatin (P=0.015, RR=2.50) were independent predicting factors affecting the probability of achieving the target PBPC and the time to reach the target PBPC collection. In addition, the total dose of cyclophosphamide the patient received significantly alters the mobilization.