Plasma thrombin-antithrombin III complexes in the diagnosis of primary hepatocellular carcinoma complicating liver cirrhosis. Detection of hypercoagulable state might be helpful in the diagnosis of primary hepatocellular carcinoma (HCC) complicating liver cirrhosis (LC). Plasma levels of thrombin-antithrombin III complex (TAT) were determined in 50 patients of LC with or without HCC. The levels were above 2 ng/ml in 80% of 25 HCC patients, but only in 12% of 25 non-HCC patients (P less than 0.01). The levels over 2 ng/ml occurred even in five of six HCC patients whose serum alpha-fetoprotein levels were below 20 ng/ml as well as in two of three patients with HCC less than 2 cm in diameter. Those levels in HCC patients were significantly decreased within 8 days after treatment with transcatheter arterial embolization or infusion of antitumor agents, without affecting plasma antithrombin III levels. These results suggest that plasma TAT levels may be useful in the diagnosis of HCC complicating LC. 