GB virus C (GBV-C), also called hepatitis G virus (HGV), occurs worldwide, but the clinical significance of this virus is still unclear. Plasma samples from 1,001 blood donors were tested by reverse transcription PCR using primers from the NS5 region and by a commercial enzyme-linked immunosorbent assay (ELISA) for the detection of immunoglobulin G antibodies against the putative envelope of HGV (anti-HGV E2). GBV-C/HGV RNA was present in the plasma from 2.5% of the blood donors, and anti-HGV E2 antibodies could be detected in 10.5% of the samples. Only one of the blood donors with viremia had elevated levels of alanine aminotransferase. Among ELISA-positive donors, there was a significantly higher percentage (16.5%) of individuals who had been treated by acupuncture than individuals who had not been given this treatment (9.4%). No other variables showed significant differences. Screening of medical records from 401 recipients of blood from PCR-positive donors revealed no association with liver disease. Four of 12 partners (33%) were HGV RNA positive, and sequence analyses of the strains showed that four of the couples probably were infected with the same strains, while strains from different couples were not identical. Anti-HGV E2 antibodies were detected in serum samples from four other partners. The prevalence of GBV-C/HGV among blood donors in our region is dramatically higher than the prevalence of hepatitis C virus (0.03%).