Leptin, the obese gene (ob) product, is a plasma protein synthesized exclusively in adipocytes and plays an important role in regulation of food intake and energy expenditure. The aim of the study was to compare serum leptin concentration in hemodialyzed (HD) patients and in patients undergoing continuous ambulatory peritoneal dialysis (CAPD), and to assess the relationship between leptinemia and parameters of nutritional state and inflammatory markers. We studied two group of patients with end-stage renal failure: 52 hemodialyzed individuals aged 24-74 years and 19 peritoneally dialyzed patients aged 20-70 years. Serum hemoglobin concentration, erythrocyte count, cholesterol, triglycerides, total protein, albumin, urea before and after HD, urea in CAPD patients, CRP, peritoneal protein loss were determined by standard laboratory methods. Serum leptin concentration before and after HD, in CAPD patients, leptin in ultrafiltrate and in peritoneal fluid was measured by commercially available radioimmunoassay. Plasma TNF-alpha and IL-1 concentration were measured by ELISA. We found that the serum leptin concentration was higher in hemodialyzed patients than in peritoneal dialyzed individuals (19.97 +/- 22.57 ng/mL vs 3.52 +/- 4.39 ng/mL, p < 0.01). There was a significant correlation between serum leptin levels and BMI in both studied groups (r = 0.81, p < 0.01 in HD group; r = 0.46, p < 0.05 in CAPD group). Concentrations of inflammatory markers (CRP, TNF-alpha, IL-1) were higher in hemodialyzed patients. Peritoneally dialyzed patients presented higher serum lipid concentrations (cholesterol and triglycerides) (p < 0.05). Neither inflammatory markers concentrations nor serum lipid concentrations correlate with the serum concentration of leptin.