A significant challenge in the epidemiological investigation of recreational waterborne disease is the establishment of a definite association between exposure to a contaminated water and infection. An increase in specific antibodies as a result of infection is a potent measure of disease exposure and its determination would enhance epidemiological studies of waterborne diseases. We report on the automated detection of HAV antibodies in crevicular fluid and its use in a field study. The method is easy to use, non-invasive, could be applied to volunteers of all ages and is comparable in sensitivity to serological procedures. Application to an epidemiological study of water recreationalists demonstrated that surfers were three times more likely to be immune to hepatitis A virus than either wind-surfers or a control group without recreational water contact.