No specific characteristics have been identified as predictors of peripheral blood stem cells (PBSC) mobilization in healthy donors. In this study, clinical characteristics and laboratory data for 122 healthy donors who underwent apheresis on day 5 of treatment with recombinant granulocyte colony-stimulating factor (G-CSF) were retrospectively analyzed for correlations with CD34(+) cell mobilization. The variables that were analyzed included age, sex, body weight, basal complete blood count, and maximum white blood count (WBC) before apheresis, G-CSF type, and dosage. Median age and body weight were 42.5 years (range 16-65) and 72.5 kg (range 47-121), respectively. By univariate analysis, male sex (P = 0.007), body weight (< or = 70 vs. >70 kg, P = 0.04), and donor's age (< or = 50 vs. > 50 years; P = 0.015) were correlated with the number of CD34(+) cells mobilized. By multivariate analysis, donor's age and male sex were the only two variables that significantly predicted a high CD34(+) cell level. In conclusion, our data suggest that male sex and younger age are the only factors that significantly affect CD34(+) mobilization in healthy donors.