The aim of the study was to determine the prevalence of hepatitis E virus (HEV) infection among individuals at high risk of transmission of non-A, non-B hepatitis or sexually transmitted diseases (STDs), and to evaluate whether they have an increased risk of exposure to HEV. Serum samples from 125 thalassemia patients, 300 intravenous drug users, 420 hemodialysis patients, 263 individuals with STDs, 47 human immunodeficiency virus (HIV) infected homosexual men, and 316 healthy volunteers were tested for immunoglobulin G (IgG) and M (IgM) antibodies to HEV (anti-HEV) by enzyme immunoassays (EIAs) following a predetermined algorithm (Abbott Labs). Anti-HEV IgG was confirmed in 3/125 (2.4%) thalassemia patients, 5/300 (1.7%) intravenous drug users, 27/420 (6.4%) hemodialysis patients, 4/263 (1.5%) STD patients, 1/47 (2.1%) homosexual men, and 7/316 (2.2%) of the reference group. No patient was found positive for anti-HEV IgM. The higher prevalence which was observed in hemodialysis group was due to the confounding effect of age, as multivariate analysis showed. The anti-HEV prevalence increased significantly with age (p = 10(-4)). No significant association was found between anti-HEV, anti-HCV, and anti-HBc. In conclusion, individuals at high risk of non-A, non-B hepatitis and STDs have no increased risk of exposure to HEV and the higher prevalence of anti-HEV IgG among older subjects may be due to an epidemic form of HEV infection which occurred some decades ago, when the sanitary conditions in our country were poor.