Abstract Lethal immune reactions by the lymphocytes and plasma in children with neuroblastoma have been demonstrated against neuroblastoma cells in vitro. It is likely that these are responsible for the known so-called “spontaneous regression” of these tumors, which has been observed clinically and in in situ cases. In the light of present knowledge, it is at this time unsafe to use immune lymphocytes or serum from suitable donors in treating these children. Ways to circumvent the possible dangers of such treatments must be investigated in the laboratory. The use of the present forms of treatment, which include resection, irradiation, and chemotherapy, should be modified so that these newly recognized immune reactions are preserved, rather than destroyed.