Carbohydrate-deficient transferrin (CDT) and gamma-glutamyltransferase (GT) were evaluated as markers of alcohol dependency in two different groups of patients. Sensitivity of CDT was nearly 75% for patients hospitalized for detoxification, but lower than 50% for alcohol-dependent patients admitted to acute surgery. CDT correlated with self-reported alcohol consumption in both groups, and sensitivity increased with higher alcohol intake. Sensitivity of CDT for females in both groups was considerably lower than for males, although their alcohol consumption was not significantly different. Serum activity of GT showed almost identical performance as CDT when evaluated by receiver-operating characteristics curve analysis (ROC-analysis), but sensitivity and specificity of the two markers varied differently with both alcohol consumption and age. Among the surgical patients, the highest sensitivity of CDT was found for the middle-aged patients (36 to 50 years), whereas the highest sensitivity of GT was found for the eldest. A tendency for similar age-related differences were also observed among the patients warded for detoxification, but these differences were not statistically significant. A particular difference between the two groups was noted among the youngest patients (21 to 35 years), with a very low sensitivity of CDT (< 20%) for the surgical patients and a high sensitivity (77%) for the detoxification group. This difference was not only caused by differences in the present alcohol consumption, but would also be related to differences in drinking pattern or duration. Two commercial kits analyzing CDT were compared and ROC-analysis indicated identical performance of the two. However, a kit determining CDT as percentage of total transferrin showed a somewhat higher sensitivity among patients with low serum transferrin. We conclude that CDT and GT show variant responses to alcohol consumption in different groups of patients. The level of the two markers are related to sex, age, and alcohol consumption. Furthermore, the performance of both markers depend on the patients' history of alcohol abuse. CDT and GT are statistically independent markers and may therefore supplement each other.