Background: Four fractions of gamma-glutamyltransferase (GGT) with different molecular weight (b-, m-, sand nd f-GGT) are present in human plasma. Differential GGT fraction pattern is found in non-alcoholic liver disease (NAFLD) and chronic viral hepatitis, characterized by normal or decreased b-GGT/s-GGT (b/s) ratio, respectively. Methods: Chromatographic fractional GGT analysis was performed on plasma obtained from 51 subjects: 27 alcoholics (mean (SD), age 45 (9) years; 23 males; 14 positive for viral infection), 24 abstinents from at least 1 month (43 (12) years; 20 males; 6 positive for viral infection). Twenty-seven blood donors matched for age and gender (44 (9) years; 23 males) were selected as controls. Results: All fractions were significantly increased in alcoholics (P < 0.001), s-GGT showing the largest increase, while only m-GGT and s-GGT were elevated in abstainers (P < 0.01), in comparison with controls. The b/s ratio was significantly lower in both alcoholics and abstainers than in controls (median (25th-75th perc.