Prevalence of hepatitis G virus (HGV) was determined in a cohort of Chinese blood donors and hepatitis patients by the detection of viral RNA via reverse transcription-polymerase chain reaction. While HGV RNA was detected in only 1 of 150 healthy volunteers, the detection rate among professional blood donors was surprisingly high (21/265, 7.9%), and plasmapheresis was identified as a significant risk factor in this population. It was also shown that an elevated serum alanine aminotransferase level is not a reliable marker for HGV infection. Prevalences of HGV in patients with hepatitis C, with non-A-E hepatitis, and with hepatocellular carcinoma were relatively low (8.2%, 16.7%, and 6.1%, respectively). Striking sequence homology (>90%) shared by 5 HGV cDNA clones implicated that they belonged to the same genotype. Phylogenetic analysis of a 446-bp NS3 cDNA confirmed that this genotype was closely related to the prototype viruses.