Circulating immune complexes (CIC) may be involved in tissue damage and/or viral clearance in viral hepatitis. To assess the frequency of raised CIC in chronic hepatitis related to hepatitis B and C, IgM, IgG, and hepatitis B surface antigen (HBsAg) containing CIC were determined, by conglutinin (K) and C1q assays, in 101 patients with chronic hepatitis B alone, 24 patients with chronic hepatitis B and C, 48 patients with chronic hepatitis C alone, and 54 healthy controls. Compared to patients with hepatitis B alone, patients with dual infection had higher frequency of raised IgM-C1q CIC (P < 0.001) and IgM-K CIC (P < 0.01). There is no difference in the prevalence of HBsAg-CIC between patients with hepatitis B alone and those with dual infection. Among patients with chronic hepatitis C alone, conglutinin-binding CIC is the predominant type of raised CIC and correlated with more severe liver damage. In conclusion, CIC may play a role in the pathogenesis of chronic hepatitis C virus infection.