A short-course administration of non-glycosylated granulocyte-colony-stimulating factor (G-CSF) was investigated in 68 healthy donors (HDs) in order to collect > or = 4 x 10(6) CD34+ cells per kilogram of recipient's body weight. G-CSF was given at 10 microg/kg per day administered in two divided doses for 3 days. Leukapheresis was scheduled on day 4, 12 h after the last dose of G-CSF. A median of 35.6 circulating CD34+ cells microL(-1) (range, 3.1-185) was found on the day of leukapheresis. This allowed a median collection of CD34+ cells of 4.2 x 10(6) per kilogram of recipient's weight (range, 1.0-17.4). One single procedure was sufficient to reach the target level of CD34+ cells in 36 (53%) of 68 donors; significant correlations were found between the number of CD34+ cells collected on day 4 and the patient's sex, body-weight and volume of blood processed. A retrospective analysis was made with a historical group of HDs collected on day 5. The day 5 schedule allowed a more consistent achievement of the target cell dose with one leukapheresis (P = 0.005) and resulted in the initial collection of a significantly larger number of CD34+ cells (P = 0.006).