The ability of short-term furosemide administration to alter intrarenal hemodynamics and to modify the clinical course of acute renal failure was assessed in six patients 2 to 9 days after the onset of acute renal failure. Following renal arterial catheterization, the intraarterial administration of furosemide at a dose of 9.6 mg/min for 30 minutes failed to improve renal function as assessed either by an increase in urine output or a decrease in serum creatinine during the 4 days after administration in the five oliguric patients. In a sixth patient with nonoliguric acute renal failure, urine volume increased with a gradual decrease in blood urea nitrogen and creatinine during the week after study. Furosemide failed to alter either mean renal blood flow or its intrarenal distribution as determined at intervals of 3 to 40 minutes after its infusion. These studies demonstrate that the short-term administration of furosemide in large doses does not improve renal hemodynamics or alter the clinical course of patients with established acute oliguric renal failure.