Twenty-three seronegative women living in a mental institution were immunized with Cendehill rubella vaccine. Five others without antibody to rubella who resided in the same quarters were not immunized and served to monitor the possible introduction of wild virus into the institution. All those who received the vaccine developed significant antibody titers. Nine months following the initial vaccination, ten women were given a booster dose of vaccine; none showed an increase in antibody titers. Twenty-two months after primary immunization, the other 13 were reimmunized; only one exhibited a response. The incidence of a booster effect for the group as a whole was only 4.4%. None of the unvaccinated seronegative individuals developed specific antibody, indicating a lack of introduction of wild rubella virus into the environment.