Antibody to hepatitis E virus of IgG class (anti-HEV IgG) is regularly detected in industrialized countries, where HEV is non-endemic, at levels not exceeding 2-3%; seropositive individuals are often found in certain groups of patients and professionals exposed to an increased risk of blood-borne infections. The present study was aimed at the identification of anti-HEV IgG in patients with human immunodeficiency virus (HIV) infection, including acquired immune deficiency syndrome (AIDS), living in Russia and Belarus, an area of low anti-HEV prevalence with a moderate spread of HIV infection and AIDS. In Russia, 13 out of 117 HIV-infected patients (11.1%) were found to be anti-HEV seropositive. This differed significantly from the frequency observed in the normal population (1.7%) but not from the frequency in a matching control, high-risk group consisting of male prisoners (8.0%). No difference in the frequency of anti-HEV IgG seropositivity was found between groups of HIV-infected men subdivided by sexual orientation. The rate of anti-HEV seropositivity increased with the progression of HIV infection, reaching 43.3% in AIDS patients and 38.1% in those who died from AIDS. In Belarus, anti-HEV IgG seropositivity was not found among 20 HIV-infected subjects nor among individuals from the control risk group, which consisted of 25 intravenous drug users. In conclusion, HEV infection may have common transmission mechanisms (risk factors) with HIV infection rather than represent an additional opportunistic infection in AIDS.