The discovery of virus-specific messenger RNA in virus-induced animal tumors has led to the search for messenger RNA in human tumors that can be hybridized with the DNA of known oncogenic viruses. Attention has focused on the adenoviruses, which have produced cancer in laboratory animals and are widespread in man, and on three papovaviruses that have been isolated in human disease and which are oncogenic in hamsters. In other research, the association between human infection with herpesivurs type 2, which is likewise oncogenic in hamsters, and invasive carcinoma of the cervix is being examined. An experimental vaccine is being developed, and nonhuman primate models are being studied as part of this work. Epstein-Barr virus is still another suspected agent of human malignancies, specifically Burkitt's lymphoma and postnasal carcinoma. High prevalence of antigen to hepatitis B virus has been seen to correlate with high incidence of primary liver cell carcinoma, and studies are attempting to elucidate the relationship.