We describe three patients with type-1 autoimmune chronic hepatitis whose liver disease was exacerbated by alpha-interferon. In all cases, chronic hepatitis was initially considered to be caused by infection with hepatitis C virus (HCV), exacerbation of disease occurred 4 to 8 weeks after alpha-interferon therapy was begun. Infection with HCV was not confirmed by second-generation specific tests. Elevated titers of antinuclear and anti-smoth-muscle antibodies were diagnostic of type-1 autoimmune chronic hepatitis. All patients showed improvement after cessation of alpha-interferon and administration of corticosteroids. Exacerbation of chronic hepatitis after treatment with alpha-interferon has practical implications. It provides a clue to the diagnosis of autoimmune chronic hepatitis, and it should prompt the cessation of alpha-interferon and the administration of corticosteroids.