A new virus named hepatitis G virus (HGV) has been detected recently. Until now, no assays for the detection of antibodies against different HGV proteins have been commercially available. Therefore, a strip immunoblot assay has been established to investigate seroreactivity against recombinant structural (core) and nonstructural proteins (NS3 and NS4) of HGV produced in Escherichia coli. Seropositivity for HGV was evaluated and concordanced with HGV polymerase chain reaction (PCR) results in 709 subjects. These individuals were classified into a nonrisk or a risk group, on the basis of infection with human immunodeficiency virus (HIV) or hepatitis C virus (HCV) or frequent parenteral exposure, including hemophilia, intravenous drug addiction, receipt of blood transfusion, or hemodialysis. The nonrisk group consisted of 257 healthy blood donors with normal alanine transaminase (ALT) levels (ALT < 30 U/L) and 154 patients with suspected non-A-E hepatitis (ALT > 45 U/L). In the group of healthy blood donors, 1.9% (5 of 257) had detectable HGV viremia and 15.9% (41 of 257) showed antibody response to HGV. In the collective of patients with suspected non-A-E hepatitis, results from 1.9% of patients (3 of 154) were positive by HGV PCR, and 15.6% of patients (24 of 154) showed seropositivity against the recombinant HGV proteins. In six groups of patients (n = 298) with different risk factors, the prevalence of both HGV viremia (V) and serological reactivity (SR) was higher compared with that of the nonrisk group: V, 6.80%-35.2%; serological reactivity (SR), 25.4%-52.9%. The following conclusions can be derived from our data. HGV infection is widespread in the general population. The prevalence of antibodies against HGV or detectable HGV viremia is higher in patients with risk factors for parenteral viral transmission than in those without risk factors. The majority of HGV infections (70.2%) is self-limiting and not persistent in our collective of patients. We found no correlation between HGV viremia and clinical or biochemical signs of hepatitis in individuals without risk factors for acquiring parenterally transmitted agents.