OBJECTIVE To determine serum gamma-glutamyltransferase (GGT), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activity, and to assess their correlation with demographic and clinical findings in healthy blood donors. METHODS This cross-sectional study was performed in 934 male blood donors, aged 18 to 68 years, who consecutively attended Tehran blood transfusion service in 2006. All participants were seronegative for HBV or HCV infections, non alcohol users, and all underwent a standard interview and anthropometric tests. Clinical and biochemical parameters including AST, ALT, and GGT activities were determined. Patients taking drugs known to cause hepatic fat deposition were excluded. For AST, ALT, and GGT variables, we used 33.33 and 66.66 percentiles, so that each of them was divided into three tertiles. RESULTS Mean AST, ALT, and GGT activities were 25.26 +/- 12.58 U/L (normal range 5-35 U/L), 33.13 +/- 22.98 (normal range 5-35 U/L), and 25.11 +/- 18.32 (normal range 6-37 U/L), respectively. By univariate analyses, there were significant associations between increasing AST, ALT, or GGT tertiles and age, body weight, body mass index, and waist and hip circumferences (P<0.05). By multiple linear regression analyses, ALT was found to be positively correlated with dyslipidemia (B=6.988, P=0.038), whereas ALT and AST were negatively correlated with age. AST, ALT, and GGT levels had positive correlation with family history of liver disease (B=15.763, P<0.001), (B=32.345, P<0.001), (B=24.415, P<0.001), respectively. CONCLUSIONS Although we did not determine the cutoffs of the upper normal limits for AST, ALT, and GGT levels, we would suggest screening asymptomatic patients with dyslipidemia and also subjects with a family history of liver disease.