In children, the optimal mobilization schedule for harvesting peripheral blood progenitor cells (PBPC) is an issue of continuous research. We have studied a schedule based on high and daily divided doses of G-CSF (12 microg/kg body weight twice daily) for 4 days for PBPC priming. Toxicity related to G-CSF was observed in 13 patients (23%), mainly mild bone pain and myalgia. The median CD34(+)cell number collected was 4.4 (0.4-35 x 10(6)/kg body weight), with 46 patients achieving 2 x 10(6)/kg body weight (83.6%) after a single large volume leukapheresis. In conclusion, this mobilization schedule allows safe and efficient collection of the minimum target CD34(+) cell dose in most pediatric patients by only one procedure.