Guanylin, a 15-amino acid peptide, activates intestinal guanylate cyclase C receptor, thereby regulating intestinal fluid and electrolyte transport through the second messenger, cyclic GMP. To examine the role of the kidney in guanylin metabolism, we used a radioimmunoassay (RIA) to measure plasma concentrations of guanylin in 3 groups; normal individuals, patients who had renal disorders with normal or elevated serum creatinine levels (0.4 < Cre < 11.9 mg/dl), and patients who received hemodialysis (HD). The plasma concentration of immunoreactive guanylin in the normal individuals was 32.3 +/- 4.8 fmol/ml. The concentrations in 32 non-HD patients were correlated with their serum creatinine concentrations (r = 0.81, p < 0.0001). In 16 HD patients the plasma concentrations of immunoreactive guanylin before the start of HD were correlated with their dialysis duration (r = 0.63, p < 0.01). The plasma levels of immunoreactive guanylin in HD patients for whom EVAL membranes were used decreased one hour after the start of HD as compared with the prior levels. The plasma levels in HD patients for whom PC membranes were used showed no change. Ten kilodalton guanylin is the main component of guanylin molecules in the plasma and hemofiltrates of HD patients. These findings suggest that the kidney has a major role in the elimination and/or metabolism of guanylin. Uroguanylin, a member of the guanylin family that was recently isolated from human urine, also acts on the guanylate cyclase C receptor. Further studies of guanylin family peptides should provide a better understanding of the physiological roles of the kidney in the control of water and electrolyte balance.