The determination of carbohydrate-deficient transferrin (CDT) in serum has been suggested as a marker of alcohol abuse. We evaluated serum CDT in 199 patients admitted to our Department of Medicine using a commercially available radioimmunoassay kit for CDT. A history of alcohol consumption was obtained quantitatively by a self-administered questionnaire and qualitatively by the Munich Alcoholism Test. Using a cut-off level of 60 g ethanol per day according to the information from the questionnaire. CDT had a sensitivity of 70% and a specificity of 84%. False-positive values were primarily encountered in cases of hepatic malignoma, primary biliary cirrhosis and chronic hepatitis C. The sensitivity and specificity of CDT was superior to two other markers of chronic ethanol consumption, serum gamma-glutamyltransferase and mean cell volume, and thus proved to be the best single laboratory test for the detection of alcohol abuse.