Des-gamma-carboxyprothrombin level was measured by enzyme immunoassay in the plasma of 39 patients suffering from hepatocellular carcinoma and 26 controls. Two of these were anticoagulated by warfarin and revealed very high positive values; the remaining 24, 8 healthy subjects and 16 patients with cirrhosis or chronic hepatitis, were negative. Values indicating pathology were found in 56.40% of patients suffering from hepatocellular carcinoma. All malignancies presenting diameter < or = 3 cm were negative, while high positive levels were found in patients with more advanced neoplasia. The alpha-fetoprotein was increased in 43.58% of the patients with hepatocellular carcinoma and in 6.25% of controls with chronic liver diseases. Positive values for both des-gamma-carboxyprothrombin and alpha- fetoprotein were detected in 12/39 patients. An increase of sensitivity (from 43.58 to 69.23%) in detecting hepatocellular carcinoma was found by the complementary use of the two markers relative to sole use of alpha-fetoprotein.