Background: Serum gamma-glutamyltransferase (GGT) activity is a sensitive but non-specific marker of non-alcoholic fatty liver disease (NAFLD). Recently, four GGT fractions (big-, medium-, small-, free-GGT) were described in humans. Aim: We aimed to investigate whether a specific GGT fraction pattern is associated with NAFLD. Methods: Gamma-glutamyltransferase fractions were determined in patients with NAFLD (n = 90), and compared with those in control subjects (n = 70), and chronic hepatitis C (CHC, n = 45) age and gender matched. Results: Total GGT was elevated in NAFLD as compared to controls (median, 25°–75°percentile: 39.4, 20.0– 82.0 U/L vs. 18.4, 13.2–24.9 U/L respectively, P