To test the value of carbohydrate-deficient transferrin (CDT) as a marker for chronic alcohol consumption, its concentration was measured in the serum of 74 patients (48 men, 26 women; mean age 48 [18-71] years) with various alcohol-related liver diseases, ten patients (six men, four women; mean age 61 [24-90] years) with non-alcohol related liver diseases and 30 healthy controls (12 men, 18 women; mean age 37 [19-84] years). In the healthy women the mean CDT concentration was 19.7 +/- 6.1 U/L, in healthy men 15.4 +/- 4.1 U/l (P < 0.05). The upper limit of normal (mean + 2 standard deviations) was 31.9 U/l in women and 23.6 U/l in men. Serum CDT levels were significantly raised in chronic alcohol abuse, depending on the degree of liver damage. The CDT level in alcohol-dependent women without liver disease was 31.1 +/- 4.3 U/l (P < 0.05), while in those with liver damage it was 42.3 +/- 14.2 U/l (not significant). The mean CDT concentration in male alcoholics without liver damage was 35.5 +/- 5.0 U/l (P < 0.01 compared with controls). In male alcoholics with liver damage the mean CDT level was 53.4 +/- 9.0 U/l (P < 0.001). In none of the ten patients with non-alcohol related liver disease was the CDT level above the upper limit of normal. The sensitivity of CDT as a marker for chronic alcohol consumption was 57% (42% for women, 65% for men) with a 100% specificity. For serum-gamma-glutamyl transferase the sensitivity was 87%, but its specificity only 73%. Because of its high specificity the serum CDT level is an added useful marker for demonstrating chronic alcohol consumption.