Hepatocyte paraffin 1 (Hep Par 1), a monoclonal antibody recognizing an antigen thought to be specific for hepatocyte mitochondria, is considered the most specific and sensitive marker of normal and neoplastic hepatocytes and has been used in diagnosing hepatocellular carcinomas. Recent data suggest that the specificity of Hep Par 1 for hepatic neoplasms is not absolute; nonhepatic neoplasms might express this marker. We assessed the value of Hep Par 1 in the diagnosis of cutaneous metastases of visceral tumors by immunostaining 65 biopsy or excision specimens with Hep Par 1. Hepatocarcinomas (primary and metastatic to the skin) showed specific (coarse granular intracytoplasmic) immunoreactivity. A similar reactivity pattern was found in 5 of 10 metastases of bronchial adenocarcinoma. Nonspecific (weak, nongranular) cytoplasmic immunoreactivity was observed in 5 cases of nonhepatic skin metastases. Hep Par 1 seems to be a sensitive marker of hepatocellular carcinomas metastatic to the skin, but its specificity is not absolute because it might be expressed in metastases of nonhepatic tumors, namely bronchial adenocarcinomas. Hep Par 1 should be used with caution in the investigation of cutaneous metastases from an unknown primary site, preferably in conjunction with other markers of neoplastic hepatocytes.