OBJECTIVE Immune reconstitution was studied in 30 children who had received purged autologous bone marrow transplantation for neuroblastoma or acute myeloid leukemia (AML). METHODS Patients with neuroblastoma received high-dose chemotherapy and total body irradiation, and patients with AML received chemotherapy alone. Marrows were purged ex vivo with either antineuroblastoma monoclonal antibodies (neuroblastoma) or 4-hydroperoxycyclophosphamide (AML). Lymphocyte subsets, mitogen stimulation studies, and immunoglobulin levels were studied every 4 months. RESULTS There were no significant differences between the two groups of patients in lymphocyte number or subsets over time. In both groups, CD2+ and CD4+ cells were below normal in 33% of patients at 12 months. CD4+/CD8+ ratios were below normal for up to 8 months after transplantation and natural killer cells were elevated for up to 2 years in most patients. Median IgG and IgA levels were below the age mean even at 2 years after transplantation, although patients with AML had significantly higher IgG levels at 12 months compared with those with neuroblastoma. Lymphocyte proliferative responses to mitogens were markedly reduced at 4 months but returned to normal at 8 months. Despite the delay in immune reconstitution, there were no life-threatening infections. CONCLUSIONS There appeared to be little difference in the overall kinetics of immune reconstitution between the children with neuroblastoma, who received total body irradiation and high-dose chemotherapy, and those with AML, who received high-dose chemotherapy alone as their pretransplant preparative regimen.