The present study was undertaken to determine the prevalence of cytomegalovirus infections among 4,790 infants and children living in the Bari area. Serum antibodies were measured by a microneutralization test. IgM antibodies were measured with a capture immunoenzymatic test. A high incidence of maternally derived antibody was found during the first 6 months of life (92.8%). The positivity rate declined during the second 6 months (86.9%) and between 1 and 4 years (86.6%) and increased again between 4 and 7 years (89.1%), between 7 and 10 years (90.6%) and between 10 and 15 years (91.7%). IgM-specific antibodies were found at a titer of 1:30 or greater in 42 subjects (0.9%) who also exhibited neutralizing antibody titers > or = 1:256. Infection in Bari is characteristic of cytomegalovirus-endemic areas where maternally derived immunity is immediately replaced by immunity due to primary infection.