Abstract Circulating virion-antibody complex has been identified previously in association with chronic phase of HCV infection. In the present study, we investigated whether and to what extent GBV-C virions in the circulation of infected host are bound to IgG. To enable direct comparison between GBV-C and HCV, we used plasmas that were positive for both GBV-C and HCV RNAs. Diluted plasma was incubated with anti-human IgG, centrifuged, and divided into supernatant and pellet, and viral RNA titers were compared between the two fractions. In all nine samples examined, HCV RNA was detected in the pellet with higher titers than in the supernatant. By contrast, GBV-C RNA titers in the supernatant were higher than or equal to those in the pellet, except for only one case. Our results suggest that GBV-C virions are less associated with IgG than HCV virions are, and this may reflect the absence of hypervariable regions within envelope proteins of GBV-C.