Herpesvirus hominis type 2 antibodies were present in 35.7% of patients who subsequently developed carcinoma in situ of the cervix, whereas type 2 antibodies were present in 7.1% of matched controls who did not develop carcinoma in situ during the same period of observation. Type 2 antibodies were present in a significantly greater percent of patients with carcinoma in situ (42.0) than matched controls (17.7). After cervical conization and presumptive cure of carcinoma in situ, however, type 2 antibodies were present in a smaller percent of patients (9.1) than matched controls (31.8). The data suggests that previous herpesvirus type 2 infection is associated not only with the precursory stages of invasive cancer, but also precedes the earliest intraepithelial changes which develop into carcinoma in situ.