Abstract: Aims/Background: Many epidemiological studies of new hepatitis viruses, including GB virus C (GBV-C) and hepatitis G virus (HGV), have used polymerase chain reaction (PCR) primers designed for the third nonstructural region (NS3R). However, a homology study of GBV-C and HGV genomes revealed that the 5′ untranslated region (5'UTR) was more conserved than NS3R. Methods: We attempted to detect GBV-C/HGV using PCR primers corresponding to the 5′ UTR, and compared its incidence to that derived from NS3R primers. Furthermore, PCR products amplified using the 5′ UTR primers were sequenced and subjected to phylogenetic analysis. Results: In patients with chronic hepatitis C, the prevalence of GBV-C/HGV by PCR with the NS3R and 5′ UTR primers was 5.1% (4/78) and 17.9% (14/78), respectively, and in patients on hemodialysis, it was 0% (0/81) and 5.9% (5/85), respectively. We could not detect GBV-C/HGV in patients with non-A-C liver disease. The incidence of GBV-C/HGV by 5′ UTR primers was higher than by NS3R primers. After DNA sequencing at 5′ UTR, phylogenetic analysis showed two types of GBV-C/HGV, Jap and HGV types. Conclusion: 5′ UTR primers proved highly sensitive for detection of GBV-C/HGV and were superior to the NS3R primers.