A cytokeratin immunohistochemical study was performed on 40 liver biopsies diagnosed as alcoholic liver disease to further investigate the cytoskeletal changes occurring in this disease. On paraffin sections of 29 cases, a variable number of hepatocytes were reactive with a polyclonal antiserum that normally stains only bile ducts. Using monoclonal antibodies specific for a single cytokeratin polypeptide on cryostat sections, a variable number of hepatocytes were immunoreactive for cytokeratin no. 7 in 23 cases and also for cytokeratin no. 19 in seven cases. Both these polypeptides are restricted to bile duct cells in the normal liver. The number of hepatocytes positive for bile duct-type cytokeratins increased and their location changed with the severity of the disease. Mallory bodies were reactive with monoclonal antibodies CAM 5.2 and anti-cytokeratin no. 18 but unreactive with anti-cytokeratin no. 8. except in one case. In two cases, Mallory bodies reactive with both monoclonal antibodies anti-cytokeratin no. 7 and anti-cytokeratin no. 19 were found. These results clearly indicate that hepatocytes in alcoholic liver disease can express immunoreactivity for bile duct-type cytokeratins. Our data also demonstrate heterogeneity in the composition of Mallory bodies. Whether hepatocytes expressing bile duct-type cytokeratins are the precursors of Mallory body-containing cells is not clear at present.