The role of the biological alcohol marker carbohydrate-deficient transferrin (CDT) in the diagnosis of alcoholism is not clear, but the measurement of CDT appears to have high diagnostic accuracy in certain high-risk populations. The aim of this study was to compare the diagnostic accuracy of CDT with gamma-glutamyltransferase (GGT) and mean corpuscular cell volume (MCV) in a general practice population to determine the relative utility and diagnostic accuracy of the three tests in the diagnosis of alcoholism. Three alcohol drinking patterns were used to stratify the population, namely irregular excessive, < 13 drinks/week) regular excessive, and very excessive (>30 drinks/week). The sensitivity (S), specificity (SP), and predictive values (PPV, NPV)) of the three markers in the three sub-populations were compared in 524 men attending a general practice clinic. In all excessive drinkers, the CDT and MCV had S of 31% and 17%, SP of 92% and 93%, PPV of 43% and 32%, and NPV of 88% and 86% respectively. The performance of all these tests was too low to be useful as screening procedures in the general population. Despite the limitations of this study, CDT seems to be the best marker available for significant alcoholism, but the application of this test should occur in the appropriate clinical setting.