The effect of furosemide on the development of the acute ischaemic renal failure in the dog was studied. 11 canine kidneys were used as controls (group I) and 12 as a group where furosemide (6–8 mg/kg of body weight) was given (group II) immediately after releasing the clamps. Urine volume and sodium clearance were found significantly higher in the second group of kidneys during a period of 60 min after restoration of the blood flow to the kidney. Urea clearances remained low with no noted difference between the 2 groups. By the end of the first hour osmolar and potassium clearances were found to be significantly higher in the second group. The above findings suggest that furosemide given after an induction of acute ischaemic renal failure in the dog provides, up to the 1st hour after recirculation, some benefit in water and solute excretion but no benefit in urea clearance.