Background : Gamma-glutamyl transferase(GGT) has found wide application as a diagnostic test in hepatobiliary disease, and has been used as the best single marker of alcohol intake. In spite of the wide use of GGT in clinical practice, knowledge concerning the distribution and the determinants of this risk factor in the normal population is spared in Korea. We tried to obtain a better evaluation of specificity of serum GGT by analysis of a large population of health examination. Methods : GGT was measured in 17,140 males aged 17-86 years and 12,125 females aged 18-90 years screened in a health survey program. Results : In multiple regression analyses, serum GGT level showed strong positive association with fatty liver, body mass index, serum levels of AST, ALT triglyceride, uric acid, alkaline phosphatase, systolic blood pressure, and diastolic blood pressure, and weakly positive association with serum levels of creatinine, total cholesterol, and fasting blood sugar. In females, menopause were positively associated with GGT. Conclusions : An elevated serum GGT levels is a strong indicator of hepatobiliary dysfunction or fatty liver. However, proper interpretation of a serum GGT elevation should be carefully considered in correlation with clinical data and laboratory findings. (Korean J Med 57:1006-1013, 1999)