The population of Israel comprises offspring of immigrants from countries of high and low incidence of cytomegalovirus infection. To evaluate possible ethnic differences in the prevalence of antibodies against cytomegalovirus in young adults, blood samples were taken from a random sample of 422 Israeli military recruits aged 18-19 years, during 1987. Antibodies against cytomegalovirus were determined by means of ELISA. Subjects originating from North Africa or Asia had higher prevalences than those originating from Western countries (84.0% and 74.0% versus 60.0%, P < 0.001) and the differences persisted after adjustment for gender, education and socioeconomic status. The prev- valence of antibodies was significantly lower in men than in women (63.1% versus 76.5%). These findings identify subpopulations who are at increased risk of primary cytomegalovirus infection during adulthood and may be candidates for future anti-cytomegalovirus vaccines.