In this study we have attempted to classify a group of North American patients with autoimmune chronic hepatitis into types I, II, and III according to the class of autoantibody present in serum, and determine the prevalence and significance of antibody to hepatitis C virus (anti-HCV). A total of 62 patients (type I, 51; type II, 3; type III, 8) were tested with first-generation enzyme-linked immunosorbent assay (ELISA)-1. Seropositive patients were assessed by second-generation recombinant immunoblot assay (RIBA)-2 and polymerase chain reaction (PCR). Our results demonstrate that 12 (19%) of the 62 patients with autoimmune hepatitis were anti-HCV ELISA-1 positive (type I, 9; type II, 1; type III, 2). Only one patient with type II autoimmune hepatitis was reactive by RIBA-2 and PCR. Eight of the 12 seropositive patients entered remission after corticosteroid therapy and seven of them became seronegative by ELISA-1. The RIBA-2 and PCR reactive patient did not respond to immunosuppressive therapy and remained seropositive. We conclude that there is a low prevalence of anti-HCV antibody in autoimmune hepatitis. Results based only on ELISA-1 anti-HCV testing can be misleading, and second-generation testing is necessary to recognize the presence of HCV infection. The fact that the only RIBA-2 reactive patient had type II autoimmune hepatitis may suggest a role for HCV infection in the pathogenesis of this condition. Nevertheless, corticosteroid therapy remains effective in those patients who are ELISA-1 seropositive, but RIBA-2 and PCR nonreactive.