Viral infections have been implicated in the pathogenesis of several malignancies. A high incidence of the Epstein-Barr virus (EBV) genome and increased EBV-specific antibody titers were frequently observed in Hodgkin's disease. Some epidemiologic and clinical similarities have been demonstrated between Hodgkin's disease and human testicular germ-cell carcinoma. However, we investigated testicular biopsies from 16 patients with testicular cancer and 16 noncancer controls for the presence of EBV, cytomegalovirus (CMV), and herpes simplex virus (HSV) genomes with in situ hybridization and evaluated serum antibodies against EBV, CMV, and mumps among 52 patients with testicular carcinoma and 54 age-matched controls without cancer. There were no statistically significant differences in increased virus titer between patients with testicular cancer and controls, and we detected no EBV or CMV DNA in tumor cells, although the HSV genome was found in 50% of the testicular-tumor patients and 37.5% of controls. The findings suggest that viral infections have no direct role in the etiology of testicular carcinoma. The detection of HSV DNA in both tumor patients and controls might be a sign of latent infection, rather than a risk factor for testicular cancer.