Inhibin is a peptide hormone produced by ovarian granulosa cells. During a recent study investigating the immunohistochemical staining of ovarian granulosa cell tumours and other neoplasms with an anti-inhibin monoclonal antibody, we identified strong cytoplasmic staining of hepatocytes. In the present study we investigated the immunostaining of hepatocellular carcinoma and other neoplasms involving the liver with anti-inhibin to determine whether the antibody may be of value in the differential diagnosis of hepatic neoplasms. Immunostaining for alpha-fetoprotein was also performed. With anti-inhibin there was positive, generally strong, cytoplasmic staining of 17 of 19 cases of hepatocellular carcinoma, including the pleomorphic and glandular variants. There was positive staining of six of 20 cases of adenocarcinoma. In these, positive staining was generally focal, of weak intensity and involved the luminal surface of neoplastic glands. There was no staining of five cases of neuroendocrine tumour. There was positive staining for alpha-fetoprotein in 13 of 19 cases of hepatocellular carcinoma and in two of 20 cases of adenocarcinoma but no staining of neuroendocrine tumours. Immunostaining with anti-inhibin antibody may be of value in the differentiation of hepatocellular carcinoma from other neoplasms involving the liver. The antibody is a more sensitive, but less specific, immunohistochemical marker for hepatocellular carcinoma than is alpha-fetoprotein.