The amounts of antigens in the serum of patients with various types of cancer and benign diseases were measured in order to clinically evaluate the NCC-ST-439 EIA kit. From the results of measurements in 583 healthy persons, cut-off values of 4.5 U/ml for males and females 50 years or older and 7.0 U/ml for females 49 or younger were set. The false-positive rate for healthy persons at this time was 5.0%. The positive rates for malignant tumors at these cut-off values were 58.9% for pancreatic carcinoma, 53.1% for cholangiocarcinoma, 41.9% for mammary carcinoma, 36.6% for rectal and colonic carcinoma, 33.3% for hepatocellular carcinoma and 35.3% for carcinoma as a whole. The false-positive rates for benign diseases were 14.0% for pancreatic disease, 9.7% for liver disease, 8.0% for biliary duct disease and 8.3% for benign diseases as a whole. These rates were low when compared with those for other tumor markers. These results showed that NCC-ST-439 is a tumor marker with a high degree of specificity.