The concentration of abnormal prothrombin, or the protein induced by vitamin K absence or antagonist II (PIVKA-II) in 102 patients with hepatic disorders was measured by an enzyme immunoassay method. The concentration of PIVKA-II in the plasma was elevated in 11 out of 18 patients with hepatocellular carcinoma and also in a patient with hepatoblastoma. There was no correlation between serum alpha-fetoprotein and plasma PIVKA-II levels. The PIVKA-II level was normal in 11 patients who had metastatic carcinoma or cholangiocellular carcinoma. Moreover, benign diseases of the liver did not cause an elevation in PIVKA-II. PIVKA-II might be an useful marker of hepatocellular carcinoma because, like alpha-fetoprotein, its level changes in close relation to the effects of treatment.