An antiserum to carcinoembryonic antigen (CEA) and a monoclonal antibody to cytokeratin 19 (CK 19) were studied for their suitability as diagnostic reagents for the differential diagnosis of primary and secondary malignant epithelial tumours of the liver, on paraffin sections. With the antiserum to CEA, positive bile canalicular structures were found in 60 per cent of the hepatocellular carcinomas. All the cholangiocarcinomas and 66.6 per cent of the metastatic carcinomas were positive for CEA, without displaying a canalicular staining pattern. All the hepatocellular carcinomas were negative for CK 19. All the cholangiocellular carcinomas and the metastatic carcinomas were positive for CK 19. This staining profile may prove helpful in difficult diagnostic cases.