The effects of cromakalin, a potassium channel opener, on renal hemodynamics and renal function were investigated in pentobarbital-anesthetized dogs. Intrarenal infusion of cromakalim at 0.5 micrograms/kg/min resulted in significant increases in renal blood flow (RBF), glomerular filtration rate (GFR), urine flow, and renin release. The urinary excretion rate of sodium increased by the same proportion as that of calcium. Free water reabsorption rate/osmolar clearance did not significantly change throughout the experiments. These data suggest that cromakalim did not inhibit sodium transport at the medullary portion of the ascending limb of Henle's loop and may have increased the delivery of sodium to Henle's loop. Intrarenal infusion of nicardipine increased RBF, GFR, urine flow, and the urinary excretion of electrolytes (Na, K, and Ca). The renal effects of cromakalim were very similar to those of nicardipine. Cromakalim was superimposed on a nicardipine infusion of a maximal effective dose. Superimposition of cromakalim to the nicardipine infusion did not cause any additional changes in renal hemodynamics and renal function. These data suggest that cromakalim and nicardipine exert their effects on renal hemodynamics and function via the same pathway.