Effects of K-351 (3,4-dihydro-8-(2-hydroxy-3-isopropyl-aminopropoxy)-3-nitroxy++ +-2H-1-benzopyran) on hemodynamics and renin release were investigated in pentobarbital anesthetized dogs. K-351 (0.3 mg/kg, i.v.) significantly decreased systemic blood pressure, heart rate, mesenteric blood flow, and renin secretion rate without change in renal blood flow. Degree of hypotension and basal plasma renin activity showed significant correlation. In indomethacin-treated (5 mg/kg, i.v.) dogs, K-351 decreased renal blood flow and caused smaller decrease in systemic blood pressure and larger suppression of renin secretion rate than in non-treated dogs. These results suggest that the hypotensive effect of K-351 may be due in part to suppression of the renin-angiotensin system and may be modulated by the prostaglandin system.