A serologic survey was conducted on a population-based representative sample of 521 18-year-old soldiers recruited to the Israel Defence Forces in 1997. The prevalence of neutralizing antibodies and geometric mean titers (GMTs) against the three types of poliovirus (Mahoney, MEF and Saukett strains) were found to be 98.7% (GMT--169.95), 99.6% (GMT--297.14) and 96.4% (GMT - 59.48), respectively. These GMTs are markedly lower than those recorded 4 years after booster vaccination carried out during a 1988 polio outbreak, and suggest a decline in immunity against polio among young adults. These findings support the policy of routine revaccination of children and adolescents in countries at risk of imported polioviruses and of revaccination of adults traveling to areas to which polio is endemic.