Study of prevalence of hepatitis G virus (HGV) markers in different risk groups showed the presence of HGV RNA in 3.2% blood donors, 24.2% patients with hepatitis C (HCV), and 28% patients with hemophilia. HGV antibodies were detected in 11.3% donors, 16.0% patients with HCV, 13.4% patients with hemophilia, and 8.5% HIV-infected subjects. Anti-E1 HGV were more often detected in the absence of HGV RNA. Antibodies to HGV E2 protein were significantly more often detected in adult HCV patients but not in adolescent patients aged 8-15 years.