An epidemiological study of hepatitis A and enteroviruses was conducted in a military diving training school, by evaluating the viral contamination of water using an ultrafiltration concentration technique, and assessing seroconversion and the presence of virus in stool specimens obtained from 109 divers and 48 controls. Three of 29 water specimens were positive for enterovirus by cell culture and 9 by molecular hybridization. There was little or no risk of virus infection during the training course (49 h exposure) because there was no significant difference between divers and controls for both viral isolation and seroconversion. However, a higher percentage of coxsackievirus B4 and B5 seropositive divers suggests that these were more exposed during previous water training. No hepatitis A virus (HAV) detection and no seroconversion to HAV was observed. The rate of HAV seropositive subjects was 17% in this 24.5-year-old population.