To investigate the mechanism(s) of degradation of leptin, the protein product of ob (obese) gene, we measured serum leptin levels in 70 patients with chronic renal failure (CRF). The median of serum leptin concentrations of 36 male and 34 female patients with CRF were 7.3 ng/ml ranging from 0.5 to 39.0 ng/ml and 34.9 ng/ml from 1.1 to 76.1 ng/ml, respectively, while those of 29 male and 29 female healthy subjects were 5.8 ng/ml ranging from 0.5 to 37.7 ng/ml and 12.0 ng/ml from 2.0 to 45.2 ng/ml, respectively. The difference in male and female serum leptin concentrations between CRF group and the normal counterpart was statistically significant (p<0.005 and p<0.05, respectively). However, there was no significant correlation, either between serum creatinine or BUN, and serum leptin concentrations. These findings suggest that leptin is degraded and/or filtered in renal tissue.