In the past few years there have been a number of reports correlating a high frequency of herpes simplex virus type 2 (HS V-2) infection with lesions of the uterine cervix. These studies have used a clinical history of herpetic infection or the demonstration of herpetic antibodies in the cancer patients. The present study was performed to evaluate any possible carcinogenic activity of the formalin-inoculated herpes simplex virus type 2 in the reproductive tract of the female mouse. This approach to the study was selected because of previous experience with a model system of carcinogenesis of the cervix uteri using coal tar hydrocarbons. Cytologic and histologic preparations from experimental animals and controls are presented to demonstrate the mucosal alterations and tumors observed in the animals. Nominvasive lesions of the cervix were identified in 76.8% and invasive adenocarcinoma detected in 30.2% of the mice.