Autoimmune chronic active hepatitis is a disease of unknown aetiology in which a dense mononuclear cell infiltratc in the portal areas of the liver is associated with ongoing necrosis of periportal hepatocytes. The finding of autoantibodies in serum, an increased frequently of HLA B8 DR3. a female predominance. an association with autoimmune diseases and the histological features all suggest a role for immunological reactions in the pathogenesis. Various immunological reactions have been demonstrated in vitro which could be of relevance to pathogenesis, including antibodies in serum directed against antigens expressed on the liver cell membrane. antibody-dependent cell-mediated cytotoxicity for autologous hepatocytes. T cell sensitisation to undefined hepatocyte antigen(s) and both antigen- and non-antigen-specific suppressor T cell defects. However, it is still unclear how these various phenomena interact in vivo and further studies are required to clarify their exact role in pathogenesis.