Harvesting of peripheral blood stem cells (PBSC) with cell separators has become a safe procedure used in many centers. However, when PBSC harvesting in small children is considered, problems due to the small volume, loss of protein and red cell trapping arise. Priming the tubing of the cell separator with either albumin or red cells is necessary in children with a blood volume of less than 1500 mL. Ten children aged from 0.8 to 5 years underwent PBSC-apheresis without major problems despite low blood volume. Forty-one children with various malignancies had a total of 189 PBSC-aphereses with a median of 5 phereses for an individual patient. Harvesting of PBSC was started after recovering from neutropenia following scheduled chemotherapy. An average of 3.7 x 10(4)/kg CFU-GM per child was harvested. Sustained engraftment after myeloablative chemotherapy could be achieved when the dose of the retransfused PBSCs was greater than 3 x 10(4)/kg. Long-lasting complete remission was observed in 5 out of 25 patients.