Leptin, the ob gene product, act to suppress appetite. Its relation to both anorexia and malnutrition in chronic renal failure is evaluated. Our study demonstrated that serum free leptin level was significantly elevated in patients on hemodialysis as well as in those on conservative treatment in comparison to normal controls. Elevated leptin level may be one of these factors decreasing appetite and food intake and increasing energy expenditure. There was also positive relationship between serum free leptin level and body mass index (BMI) in ESRD patients on conservative treatment as well as in normal subjects.