Hamsters were inoculated with varied regimens of adenovirus type 12 and complete
Freund's adjuvanr neonatally, and/or during the latent period preceding appearance of tumors. Virus andlor adjuvant were administered either separately or together as emulsions. In all instances adjuvant treatment up to one week of age reduced the incidence of tumors as compared to that in animals receiving a single dose of virus. Complement-fixing antibodies to virion or '' TI' antigens were not demonstrable in animals failing to develop tumors following neonatal inoculation of virus with or without a4uvant. However, subsequent administration of virus with or without adjuvant led to production of high titer antibodies, so that the first injection of virus had not made the animals tolerant to virion or '' T '' antigens. Administration of virus/adjuvant emulsions afrer the 5th or 6th day of life produced high titers of anri-virion antibodies regardless of tumor production. Only animals with tumors produced measurable quantities of anti-T antibody. These results suggest that oncogenesis by adenovirus can be impeded by non-specific immunological stimuli during the latent period.