Simultaneous comparative assessment of tumor contamination in bone marrow aspirates and peripheral blood stem cell collections using immunocytochemical techniques was done in 6 children with neuroectodermal tumors. In 3 neuroblastoma patients tumor cells were detected in 5 of 16 marrow samples but not in peripheral blood stem cells. Clonogenic tumor cell reinfusion in the autologous support setting may be avoided in neuroblastoma patients by using peripheral blood stem cells.