Peripheral blood progenitor cells (PBPC) are substituting bone marrow as a source of stem cells for either autologous or allogeneic hematopoietic transplantation. Several papers have been published on the experience of various groups in their mobilization and transplantation in children. Some technical problems have derived from the size of the patient or donor in the pediatric setting. Thereby, there is some concern regarding leukapheresis in very small children (weighing less than 15-20 kg). This paper summarizes our own data and that of other groups for the mobilization and collection of PBPC in the smallest children. Data from the literature show that mobilization with cytokines alone or in combination with chemotherapy is well tolerated by these patients. Pediatric donors may be used for allogeneic transplantation with no higher incidence of complications. PBPC collection even in the smallest children is a safe and efficient procedure when performed by experienced apheresis teams.