Hypotheses concerning possible modes of transmission of cytomegalovirus were tested by the use of questionnaires and sera obtained from a random sample of 894 women aged 18–69 years of age from a community in South Wales. In a multiple regression analysis married and single women were treated separately. Of a total of 11 independent variables considered, only four were significantly associated with seropositivity in the case of married women: age, number of siblings, husband's social class and father's unemployment. In the case of single women only age and father's social class remained statistically significant. The data is consistent with the hypothesis that the majority of antibody to cytomegalovirus in this community is acquired by means of close personal contact, probably by a salivary route. Further data based on longitudinal study of seropositives may be helpful in testing this hypothesis.