Viral antibodies were determined in paired maternal and cord blood sera of 258 consecutive deliveries. Antibodies to Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpes simplex type 1 (HSV-1), adenovirus (ADV), and varicella zoster (VZV) were tested by indirect immunofluorescence and to rubella (RUB) by hemagglutination inhibition. Analysis of the overall pattern of differences between maternal and cord blood showed a highly significant difference for all six viruses. Analysis regarding individual viruses showed significantly higher titers to CMV and RUB in cord blood, a higher titer to VZV in maternal blood, and similar levels of antibodies to EBV, HSV-1, and ADV in maternal and cord blood. Infants with one or more risk indicators (weight less than 3 kg, Apgar score less than or equal to 7, clinical jaundice, meconium-stained amniotic fluid, respiratory distress syndrome) were defined as "at risk." Infants free of such indicators were defined as "normal." Significantly lower antibody levels to all six viruses were found in both maternal and cord blood of the "at risk" as compared to the "normal" group, while the ratios between the maternal and cord blood levels remained similar. Birth defects were found to have no effect on antibody titers. These results indicate an efficient and selective transfer through the placenta of certain viral antibodies and the possible association of lower antibody production with the presence of risk indicators in the infants.