1. The malignant tumor neuroblastoma is known to have a high incidence of regression in the infant. 2. The possible role of the nerve growth factor (NGF) of Levi-Montalcini in this regression has been investigated thoroughly. With present methods and materials, we were unable to find a clinical correlation between levels of this material and the behavior of the tumor. 3. Histologic examination of neuroblastoma tumors has shown infiltraion with lymphocytes and plasma cells, suggesting an immune reaction. 4. Epidemiologic studies have shown no significant year-to-year variations in incidence over a large goegraphic area, but significant variations have been recorded within more localized areas. 5. Tests of the blood lymphocytes of neuroblastoma patients have demonstrated a lethal immune reacton to the tumor cells in tissue culture. These lymphocytes showed similar activity towards samples of all neuroblastoma tumors studied. A similar, but less constant, activity by the patients' plasma was also present. 6. The lymphocytes and plasma of some mothers of neuroblastoma patients have shown similar lethal reactivity to neuroblastoma cells. 7. Our present program for treatment includes : (a) surgical removal of as much tumor as possible, (b) local irradiation of residual tumor, and (c) the use of chemotherapy in short infrequent courses which may preserve the immune responcse. 8. Methods to augment safely the immune response in the patients against the tumor are being investigated.