An etiopathological link between hepatitis virus infection and autoimmune liver disease, in particular autoimmune hepatitis has been suggested. In some patients features of both viral and autoimmune disease are present. We have studied 352 patients with autoimmune liver disease and 507 patients with viral hepatitis for diagnostic characteristics as well as for evidence of an etiological connection. 38 of the 201 patients with hepatitis C (19%) and 42 of the 306 patients with hepatitis B (14%) had significant titres of autoantibodies (ANA, SMA or LKM). SLA autoantibodies were found exclusively in patients with autoimmune liver disease. LKM auto-antibody was found in only one of the 201 HCV patients. Evidence of past or present hepatitis B virus and past hepatitis A virus infection was most common in the hepatitis C virus patients and least common in autoimmune hepatitis. 28 of the 352 patients with autoimmune liver diseases tested positive in the second generation anti-HCV ELISA, but only five patients (two with autoimmune hepatitis, one with primary sclerosing cholangitis and two with primary biliary cirrhosis) were positive in confirmatory anti-HCV assays, and only in these could HCV-RNA be isolated. Autoimmune hepatitis patients had significantly higher transaminase, GLDH and IgG levels. HLA-B8, HLA-DR3 and HLA-DR4 were significantly more common in autoimmune hepatitis. Distinction between autoimmune liver disease and viral hepatitis C could be made reliably on clinical and laboratory grounds. Our data show that a link between hepatitis A, B, or C virus infection and autoimmune liver diseases is highly unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)