Hepatitis G virus(HGV) is a new RNA virus that is most closely related to members of the Flaviviridae family. HGV RNA was found in only a low percentage of patients with either acute or chronic non-A-E hepatitis. HGV appears to co-infect or superinfect in 10-15% of HCV infections, and in 5-15% of HBV infections. The prevalence of HGV infection(0.8%) among voluntary blood donor in Japan is similar to that for HCV infection. A history of blood transfusion was obtained in 50-60% of HGV RNA positive subjects. HGV was also detected in about 10% of hemodialysis patients. Finally, isolated HGV infection appears to have a low disease burden.