Women seropositive for Epstein-Barr virus (EBV) were studied during pregnancy for reactivation of latent, persistent infection. Individual women usually (94%) maintained constant titers of antibodies to EBV-specific antigens, including viral capsid antigen, early antigen, and EBV-associated nuclear antigen. The geometric mean titer of the EBV-specific antibodies was constant throughout gestation. Pregnant women did, however, differ from control subjects in that they significantly more often had antibodies to early antigen (anti-EA) (55% vs. 22%-32%). Infants born to women with anti-EA had the same incidence of low birth weight, congenital anomalies, and neonatal jaundice as did the offspring of women without anti-EA. Within the limitations of the sample, our data suggest that reactivation of latent, persistent EBV infection occurs early during gestation but that this reactivation does not adversely affect the fetus.