The renal tubular site of action of felodipine was localized using renal clearance and recollection micropuncture techniques in the anesthetized rat. In initial renal clearance experiments, felodipine (2.75 nM/kg/min i.v. X 60 min) had no effect on mean arterial pressure or glomerular filtration but significantly increased urinary flow rate, sodium and potassium excretion. In subsequent recollection micropuncture experiments, felodipine decreased mean arterial pressure but did not affect renal blood flow or renal vascular resistance or glomerular filtration rate; absolute and fractional urinary excretion of sodium and water, but not potassium, were increased. Proximal tubular and loop of Henle sodium, potassium and water reabsorption were not affected but distal tubular and collecting duct sodium and water (not potassium) reabsorption were decreased by felodipine. Felodipine is a vasodilator antihypertensive agent which, in doses which decrease mean arterial pressure in normotensive rats, increases urinary flow rate and sodium excretion by inhibiting distal tubular and collecting duct sodium and water reabsorption; potassium reabsorption or excretion is not affected. As a vasodilator antihypertensive agent, felodipine possesses beneficial natriuretic rather than detrimental sodium retaining properties.