Autoimmune hepatitis is a disease of unknown cause. Apart from genetic markers such as HLA DR3 and HLA DR4, female predominance, hypergammaglobulinaemia and characteristic autoantibodies are diagnostic hallmarks. Several viruses have been discussed to induce autoimmune hepatitis, among them all major hepatotropic viruses, Epstein-Barr virus and herpes simplex virus. It seems that herpes viruses may be responsible in at least some cases of patients with autoimmune hepatitis type 2. Furthermore, hepatotropic viruses like hepatitis C and hepatitis D virus may cause autoimmune phenomena which are similar to those in idiopathic autoimmune hepatitis. LKM-1 antibodies in hepatitis C and LKM-3 antibodies in hepatitis D may cause diagnostic problems. LKM-1 antibodies in hepatitis C are directed either against cytochrome P450 2D6 or other yet unidentified microsomal antigens. As in hepatitis C the antimicrosomal autoantibody response in hepatitis D is more heterogeneous. These LKM-3 antibodies react with several epitopes on proteins of family 1 and 2 UDP-glucuronosyltransferases (UGT). Additional autoantibodies are seen in hepatitis D virus infection. Liver diseases are models to study autoimmune disease, drug-induced and virus-induced autoimmunity in humans.