Eight pregnant women who had varicella-zoster infections were studied. Newborn serum antibody titers approximated those of their mothers when more than 5 days elapsed between the onset of maternal varicella and delivery. When this interval was shorter, maternal antibody titers tended to exceed those of cord sera. These differences could not be attributed to the placental barrier to IgM, since maternal antibody was found to be predominantly 7S. Neonatal varicella occurred in all three infants born without detectable serum V-Z antibody yet only one of these infants was found to have a detectable antibody response. Since newborn infants were found to be limited in their ability to synthesize V-Z antibody, it is unlikely that fetal synthesis could have accounted for the antibody found in infants who had antibody titers comparable to those of their mothers. It must be assumed that some, if not all of this antibody was maternal in origin and was transported across the placenta.