Eighteen marrows from 16 patients with advanced neuroblastoma were submitted to a single or double immunomagnetic depletion procedure to purge them of tumor cells. Analysis of results showed that the CFU-GM recoveries were 59% +/- 16 (SE) and 33% +/- 16 after one or two cycles of incubation with microspheres. This led to yields of 7.8 x 10(4) and 4.1 x 10(4) CFU-GM available per kg body weight, respectively. Successful engraftment was demonstrated in all evaluable patients. However, some patients had delayed hematologic recoveries, particularly for platelets.