Kaliuretic peptide, a 20-amino acid peptide hormone synthesized in the heart, enhances urine flow twofold, whereas atrial natriuretic peptide (ANP) enhances urine flow four- to 11-fold in healthy persons. The present investigation was designed to (1) determine whether kaliuretic peptide may have beneficial diuretic effects in persons with congestive heart failure (CHF), and (2) compare its beneficial effects with ANP in the treatment of CHF. Kaliuretic peptide (100 ng/kg body weight/min) given intravenously for 60 minutes to subjects with New York Heart Association class III CHF increased urine flow fourfold (p <0.001), which was maximal 212 hours after its infusion was stopped. Kaliuretic peptide enhanced sodium excretion threefold in subjects with CHF (p <0.01). Kaliuretic peptide increased the urinary excretion rate of potassium ion and fractional excretion of potassium 3.5- and twofold (p <0.05), respectively. ANP (same concentration) did not significantly enhance urine flow. ANP enhanced sodium excretion two- to sixfold in half of the CHF subjects, whereas it had no effect on sodium excretion in the other half. ANP did not significantly increase fractional excretion of sodium but did increase fractional excretion of potassium (p <0.05) during the first 20 minutes of its infusion. ANP-infused patients with CHF became hypotensive. None became hypotensive secondary to kaliuretic peptide. These data indicate that the diuretic properties of kaliuretic peptide in persons with CHF, as opposed to those of ANP, are not diminished (but rather are increased) compared with their effects in healthy persons. In patients with CHF, kaliuretic peptide causes a natriuresis—a feature not observed in those without sodium retention.