Fifteen children 4 years of age or under (8-46 months), weight 7.8 to 17 kg, underwent 44 peripheral blood stem cell (PBSC) collections. Diagnoses included PNET/medulloblastoma (five), neuroblastoma (five), and others (five). PBSCs were collected following G-CSF/GM-CSF or chemotherapy plus G-CSF/GM-CSF mobilization. All PBSC collections were well tolerated. The average yield per collection was 6.80 x 10(8) mononuclear cells/kg (1.1-30 x 10(8)/kg) or 57.60 x 10(6) CD34+/kg (1.37 to 480 x 10(6)/kg). Eight patients underwent stem cell transplantation following myeloablative chemotherapy. Six of the eight children who received PBSC following myeloablative therapy also received autologous bone marrow (0.7 to 3.6 x 10(8) MNC/kg). One heavily pretreated patient experienced delayed hematologic reconstitution, while the remaining seven patients had a median ANC recovery to > 0.5 x 10(3)/microliter by day +10 (9-11 days) and platelets > 50 x 10(3)/microliter by day +15 (12-17 days). Seven patients received PBSCs following repetitive submyeloablative chemotherapy (ICE: ifosfamide 1.8 g/m2/day, etoposide 100 mg/m2/day x 5, carboplatin 400 mg/m2/day x 2) or other similar combination chemotherapy. Median days to recover ANC > or = 1 x 10(3)/microliter and platelets > or = 100 x 10(3)/microliter in children receiving ICE + PBSCs were 10 and 14 days, respectively, compared with 16 and 22 days in children receiving ICE + G-CSF in historical controls. In conclusion, collection and use of PBSCs to support either myeloablative chemotherapy or multicycle submyeloablative chemotherapy is well tolerated and may enhance hematological recovery in young children and infants.