Peripheral blood progenitor cells (PBPC) have became the preferred source of stem cells for autologous transplantation because of easier accessibility, rapid engraftment, and lower tumor cell contamination. In pediatric patients is very important to optimize peripheral blood stem cells (PBSC) harvesting to obtain a sufficient number of cells with a reduced number of leukapheresis. In this study we prospectively analyzed data on 43 large volume leukapheresis (LVL) from 20 consecutive low body weight pediatric patients with various malignancies. Patients' mean body weight was 16.6 kg (range, 8.9-32.0 kg), and the median age was 4 years (range, 1-10 y ears). Instead of saline, it was used irradiated and leukoreduced red blood cell (RBC) units to prime the machine in 15 patients weighting 25 kg or less. The median number of LVL was 2 (range, 1-4) and a mean of 5.2 patient's blood volume was processed per session lasting 165 min (range, 118-239). The mean number of CD34+ cells, one day before leukapheresis was 49 mm(-3) (range, 9-219). The PBPC collection yielded 24.7 x 10(8) total nucleated cells/kg (range, 6.2-74.0), 10.7 x 10(6) kg(-1) CD34+ cells (range, 3.6-53.7); 49.8 x 10(4) CFU-GM/kg (range, 6.4-198.1), and 65.6 x 10(4) BFU-E/kg (range, 7.6-198.1). The platelet count decreased significantly after each procedure 39.8 +/- 9.1 x 10(9) mm(-3) (range, 18.000-76.000) (p < 0.001). In conclusion, our data show that LVL for collection of PBPC in low weight pediatric patients is a safe and efficient procedure, but it may expose the patient to the risk of thrombocytopenia.