This antibody was developed for immunocytochemical staining of formalin-fixed, paraffin-embedded tissues. The antigen recognized by the antibody has not yet been characterized but is present in normal human hepatocytes and expressed in a majority of hepatocellular carcinomas. It fails to react with a variety of other human malignancies excluding some gastrointestinal malignancies. The antibody reacts with human liver tissue giving a distinct, granular cytoplasmic staining of hepatocytes. Bile ducts or nonparenchymal liver cells are not stained. The antibody stains the majority of hepatocellular carcinomas, including fibrolamellar variants. It fails to react with a wide variety of other malignancies.