AIMS: Alanine aminotransferase (ALT) is associated with insulin resistance, and is independent of the general metabolic measures. Gamma-glutamyltransferase (GGT) is regarded as a predictor of diabetes mellitus. We analyzed which of ALT or GGT is better tool to preestimate the development of metabolic syndrome. METHOD: A total of 1203 Koreans who visited the Institute of Health in Pusan National University Hospital from January 2005 to August 2006 were enrolled in this cross-sectional study. Their median age was 51 years old, and the prevalence of metabolic syndrome was 16.4% (n = 197). We excluded the subjects with diabetes mellitus, hypertension and viral hepatitis or those subjects with a level of alanine aminotransferase (ALT) or gamma-glutamyltransferase (r-GGT) > 80 IU/L. RESULTS: For all the patients in the metabolic syndrome group, the median homeostatic assessment of insulin resistance (HOMA-IR), the waist circumference, the fasting blood glucose level, the systolic and diastolic blood pressure were all associated with the ALT level (P < 0.05). For the nonmetabolic syndrome group, all the metabolic risk factors were associated with the ALT level (P < 0.05). On logistic regression analysis, after correction for age, alcohol intake, HOMA-IR and body mass index, the logALT maintained a highly predictive value for metabolic syndrome, and this was better than the logGGT [odds ratio (OR) of logALT: 18.489, odds ratio of logGGT: 2.024] (P < 0.001). The risk of developing metabolic syndrome was significantly higher in the above 50 percentile and the above 75 percentile of ALT than in the lowest quartile. [for men - OR: 3.6; 95% confidence interval (CI), 2.2-5.9; OR: 6.9; 95% CI: 4.3-10.9] [for women - OR: 2.7; 95% CI: 1.5-4.7; OR: 6.5; 95% CI: 3.8-11] (P < 0.001). The cut-off value of ALT by the ROC curve was 24 IU/L for men (sensitivity: 64.3%, specificity: 66%, negative predictive value: 99.5%) and 20 IU/L for women (sensitivity: 78.9%, specificity: 61.4%, negative predictive value: 84.9%). CONCLUSIONS: Even although patients can have an ALT level that's included within the upper normal level, we may consider the probability that these patients will have metabolic syndrome. Furthermore, in our analysis, the ALT level is a better predictor of metabolic syndrome than the GGT level.