The occurrence of antibodies to herpesvirus hominis types 1 and 2 was studied in Finland among patients with a neoplastic change of the uterine cervix. The following groups were studied: 220 patients with malignant or premalignant lesions of the uterine cervix, 143 control patients matched for age, socioeconomic level, marital status, home district and number of deliveries and 82 patients with breast or stomach cancer. Antibodies to HVH types 1 and 2 were determined using the neutralization test. Sera showing an index of less than or equal to 100 were accepted as positive to type 1 and those of greater than or equal to 85 as positive to type 2. Among patients with a neoplastic change of the uterine cervix the frequency of type 1 antibodies varied between 70% and 79%. In the control group the frequency was 84% and among patients with some other malignancy 91%. These differences in the frequencies of type 1 antibody were not statistically significant. Type 2 antibodies were present in 35 to 47% among dysplasia and malignancy of the cervix. In the control group it was 18% and in other malignancies 20%. The differences between these groups and the controls were almost significant, significant and highly significant, respectively. Differences could also be observed in the distribution of neutralization indexes. The average index calculated from all sera was 48 both in the control group and in the group of other malignancies, while in sera of patients with dysplasia, carcinoma in situ and invasive carcinoma the respective vlaues were 70, 66 and 79. The results are discussed in terms of the role of herpesvirus hominis type 2 in the development of cervical cancer.