Observations were maintained for a year on 642 children and 238 mothers from families of military personnel living in an open community on the Mississippi Gulf Coast. Live attenuated rubella virus vaccine prepared with the HPV-77 strain in duck embryo cell cultures was administered to 197 and withheld from 160 children without hemagglutination-inhibition antibody. Antibody responses occurred in all vaccinees, but 13 required more than one injection. Levels were relatively stable during the study period but some increased, probably due to reinfection with natural virus. Most mothers were immune and evidence of transmission of vaccine virus was not obtained. Rubella occurred but was not observed in vaccinees. Immunity could not be determined by serum antibody titer at time of rash. In newborns, antibody rapidly declined for six months and was absent by nine months.