Measles morbidity and mortality in Israel have declined since the introduction of routine vaccination, even though measles continues to occur in epidemic cycles. In this study we examined the antibody response to measles revaccination, and the effect of prior administration of immune serum globulin (ISG) on the antibody response to measles vaccine. A study group of 312 young adults in army service received the Schwartz strain measles vaccine. Serum antibody levels were studied prior to vaccination and 2 and 4 weeks after vaccination. The finding of this study show that: a) booster response occurs in those vaccinees shown to have low or undetectable prerevaccination titers of measles antibodies; b) there is no effect of administration of ISG, prior to vaccination, on the antibody response to measles vaccine; and c) at the present level of immunity to measles in the Israeli adolescent population, we still may witness periodic epidemics in populations at risk.