Maternal sera from 45 live-born infants with congenital cytomegalovirus (CMV) infection and 4 cases of legal abortion were analysed for CMV IgG and IgM. The investigation included cases from routine work and prospective studies of unselected infants. The purpose was to elucidate the relation between the maternal type and time of infection and the signs and symptoms of the offspring at birth and follow-up. Serological patterns compatible with primary maternal infection during trimesters I and II, but also with secondary infection (in at least 1 case), were associated with infant sequelae or death. Asymptomatic infant infection was found after primary infection in trimesters II and III and after secondary infection. Virus could not be isolated from some of the fetuses legally aborted due to primary maternal infection in trimester I. Attempts to demonstrate CMV IgM activity as a marker of active infection in sera from early pregnancy (period of legal abortion) were successful in only half of the 10 cases with infant sequelae or death. Symptoms at birth were prognostically serious, but the further course was sometimes uneventful even in infants with neonatal signs of cerebral infection. A few children without initial symptoms developed sequelae (impairment of hearing).