BACKGROUND: Leptin, the product of obese(ob) gene, is thought to be a lipostatic hormone that contributes to body weight regulation through modulating food intake and energy expenditure. Animals with leptin deficiency are obese and lose body weight when they are given leptin. However little is known about the physiologic actions of leptin in humans. Plasma leptin concentrations are shown to be elevated in obese humans. So far, the factors that regulate plasma leptin concentrations remain to be identified. This work is undertaken, therefore, to examine the basal leptin concentrations in lean and obese korean males, and relation between leptin concentrations, body fat and other biochemical pararneters. METHODS: We measured the height, weight, waist/ hip ratio, fasting blood glucose, insulin, total cholesterol, triglyceride, free fatty acid and leptin concentrations in 45 obese and 45 normalweight males without medical and surgical problems. RESULTS: Means of percent IBW were 136.3+/-10.3%(mean+/-SD) and 97.2+/-6.5% in obese and control group respectively. Pasting blood sugar, free fatty acid, total cholesterol concentrations were not different between obese and control group. But the insulin and triglyceride concentrations were higher in obese group than those in control group(p< 0.05). Also, the mean leptin concentrstion was higher in obese group than that in control group(5.8+/-3.5 vs 3.0+/-2.1). The leptin concentrations were not correlated with fasting blood sugar, free fatty acid, total cholesterol levels, triglyceride, insulin or age, but correlated with WHR(r2=0.203), BMI and percent IBW. CONCLUSIONS: These findings suggest that the leptin coneentrations are positively correlated with adiposity. The mean serum leptin concentrations in korean obese males were lower than those reported in other studies, probably because the subjects of this study were only males and had lower fat amount compared to other studies, and the change of body weight and calorie intake before study was not considered.