We retrospectively studied the factors affecting the rate of hematopoietic reconstitution (HR) in 118 patients with hematological malignancies who underwent peripheral blood progenitor cell (PBPC) transplantation at a single institution. The patients received a median number of 6.6 x 10(8) nucleated cells/kg corresponding to 9.5 x 10(4) (0.5-578) CFU-GM/kg and 6.8 x 10(6) (0.2-161) CD34-positive cells/kg. The median number of days to reach 500 polymorphonuclear cells/mm3 and 50,000 platelets/mm3 was 12.5 (6-93) and 14.5 (6-440) days, respectively. No patient died from infection during the aplastic phase. By multivariate analysis, we found that the dose of CFU-GM infused was the only factor that significantly affects the HR rate (p < 0.0001). Moreover, patients with acute myelogenous leukemia or those transplanted after busulfan or total-body irradiation conditioning regimens had a slower engraftment (p < 0.08). These results could lead to identifying patients who need growth factors posttransplantation and/or the reinfusion of "back-up" marrow together with PBPC.