Complement (C')-dependent neutralising cytomegalovirus (CMV) antibody titres were determined in 4150 serum samples obtained from infants and children, as well as women of childbearing age. In a smaller group of samples, C'-independent neutralising antibody titres were also measured together with their reactivity to each individual CMV structural polypeptide in addition to total CMV antibody concentration. Results showed that primary CMV infection takes place mainly in early infancy and that 30-40% women of childbearing age do not have any or have very low titres of CMV neutralising antibody. Since poor correlation was found between the results of neutralisation tests and those of enzyme immunoassay, routine testing of neutralising antibody is warranted in those subjects, such as pregnant women, at risk of CMV infection. Results of immunoblotting suggest a correlation between high titres of neutralising antibody and antibody reactivity with three proteins of MW 86, 65, 60 kDa.