A cytokeratin immunohistochemical study was performed on 38 liver biopsies from cases of primary biliary cirrhosis, primary sclerosing cholangitis, extrahepatic biliary obstruction or drug-induced liver disease in order to analyse the cytoskeletal changes in detail. On paraffin sections of 27 cases, a variable number of hepatocytes were reactive with a polyclonal anti-cytokeratin antiserum that, in the normal liver, stains bile duct cells only. On cryostat sections of 23 cases, a variable number of hepatocytes were immunoreactive with a monoclonal antibody specifically directed against cytokeratin no. 7 and were most numerous in cases of long-standing cholestasis irrespective of the aetiology. In three cases of primary sclerosing cholangitis and two cases of primary biliary cirrhosis a few hepatocytes were also weakly positive with a monoclonal antibody specific for cytokeratin no. 19. Since cytokeratins no. 7 and no. 19 are, in the normal liver, restricted to bile duct cells, these results further support the concept of 'ductular metaplasia' of hepatocytes, the mechanism of which remains unclear.