Immune serum globulin prophylaxis for foreign travellers should be reserved for those at high risk having no immunity against hepatitis A. In this study from Sweden the incidence of tourist hepatitis in different age groups was correlated to the prevalence of antibodies to hepatitis A virus (anti-HAV) in the population. 58% of individuals over 50 years had anti-HAV and travellers in these ages seldom experienced "tourist hepatitis". In younger age groups a low prevalence of anti-HAV (11%) was combined with a higher incidence of tourist hepatitis.