Clinical evaluation of plasma abnormal prothrombin (des-gamma-carboxy prothrombin) in hepatobiliary malignancies and other diseases. Des-gamma-carboxy prothrombin (DCP), a protein induced by vitamin K absence or antagonist-II (PIVKA-II) was measured in the plasma of patients with primary hepatocellular carcinoma and those with various other hepatobiliary and pancreatic diseases. DCP levels were determined by enzyme immunoassay (E-1023), using an anti-DCP monoclonal antibody. Forty-two of the 91 patients (46.2%) with hepatocellular carcinoma had abnormally elevated levels of DCP, whereas only one of the 24 patients with hepatic cirrhosis showed a slight increase. An increase was also observed in some patients with obstructive jaundice. There was no correlation between plasma levels of DCP and those of serum alpha-fetoprotein (AFP). In most patients with hepatocellular carcinoma, plasma DCP levels normalized after curative surgical resection. Plasma DCP levels were not related to the plasma concentration of vitamin K in the patients with hepatocellular carcinoma. Plasma DCP determination may be useful in the diagnosis and postoperative monitoring of the response of hepatocellular carcinoma. 