The diagnostic significance of bile carcinoembryonic antigen (CEA) in biliary diseases was clinically investigated. The determination of CEA was performed by the Z-gel method, and the normal value of plasma CEA was less than 5.0ng/ml. 1) Lyon B bile CEA showed a high value in gallbladder cancer, but was not considered to be of much diagnostic importance as it often showed a high value in cases of cholelithiasis, a benign disease. 2) gallbladder bile CEA showed slight variations, with a mean value of 86.8ng/ml in cases of cholelithiasis, but a conspicuously high value, with a mean value of 6391.9ng/ml, in cases of gallbladder cancer. This showed a high value of 7361.6ng/ml even for stage I, in which radical operation is possible, suggesting that it may be useful for differentiating between gallbladder cancer and other diseases. 3) Biliary bile CEA showed a mean value of 3.0ng/ml in cases of cholelithiasis, 34.4ng/ml in cases of gallbladder cancer and 346.9nglml in cases of biliary cancer, showing a significant increase in biliary cancer. Moreover, before treatment for decreasing jaundice the PTCD bile CEA showed a low value, less than 5.0ng/ml, and a mean value 1.8ng/ml in all cases of cholelithiasis, byt showed a mean value of 54.5ng/ml in biliary cancer. Thus, PTCD bile CEA is can be considered useful for differentiating between benign and malignant cases of obstructive jaundice.