Neuroblastomas developed in 10 of 31 Syrian hamsters inoculated intraocularly with JC virus, a human polyoma virus. The latent period was 6-11 mo. Primary tumors occurred in the abdominal cavity, pelvis, mediastinum and neck region. The origin of 1 tumor from the adrenal gland was demonstrated. Metastases were seen in the liver, bone marrow and lymph nodes. Two neuroblastomas arising in this experiment were transplanted serially in weanling hamsters, and a tissue culture cell line was established from 1 of the transplanted tumors. T[tumor]-antigen was detected in 3 of 5 primary tumors tested and in the transplanted tumors. Antibody against T-antigen was demonstrated in sera from 5 of 6 animals with neuroblastomas. Neuroblastomas also developed after combined s.c. and i.p. injection of JC virus.