Recently PBSC have been used instead of bone marrow to achieve rapid hematopoietic recovery in adults receiving myeloablative therapy. In young children several adaptations must be made because of their small size and blood volume. In the present study PBSC were collected from 10 children: median age 58 mos (range 4-76); median weight 15 kg. (range 7-22). Diagnoses included NHL-3, CNS PNET-4, neuroblastoma-1, Wilms' tumor-1, and rhabdomyosarcoma-1. PBSC were mobilized with chemotherapy and G-CSF. Vascular access was achieved using percutaneously-placed double lumen 13.5F catheters- 7 pts; double lumen 11F catheter- 1 pt; triple lumen 5.5F catheter- 1pt; and triple lumen 10F catheter- 1 pt. Leukapheresis was performed using the Cobe Spectra primed with red cells and saline. Pts were given an intravenous bolus of heparin 50 u/kg at the beginning of leukapheresis and 25 u/kg 90 minutes later. Citrate was infused continuously at a ratio of 1:25-30. Inlet flow rates were based on the pts' blood volume with a maximum ACD-A delivery of 1.1 ml./min/liter of total blood volume. 21 procedures were performed: 1-3 procedures/pt. Two-six blood volumes/procedure were processed over 100-180 minutes. The total CD34 + cell dose collected from 7 pts ranged from 1.1-49.0× 106/kg. No CD34 + cells were collected from 3 heavily pretreated pts. Six children underwent leukapheresis as outpatients. Four pts were leukapheresed during hospitalization: 2 were completing antibiotic therapy for positive blood cultures; 1 was receiving total parental nutrition; 1 remained hospitalized following completion of antibiotics for logistical purposes. The median decrease in the platelet count was 32% (range 0-48%). No pts experienced prolonged aplasia following leukapheresis. There were no episodes of hypocalcemia or bleeding. The only complication which occurred during the procedure was a decrease in body temperature by 2°C in the 4 mos old which resolved following bundling of the infant. Two catheters were removed following the collections (1 day and 2 weeks) because of infection. Leukapheresis was well tolerated by all of the pts. with a majority of the procedures performed in the outpatient setting. Based on adult engraftment studies, adequate CD34+ cells can be collected from very small infants; however, leukapheresis should be performed as early as possible in order to obtain adequate cell doses.