The present study was designed to refute or confirm the postulate that the use of high dose frusemide in chronic renal failure will increase the glomerular filtration rate (GFR). 7 patients in stable chronic renal failure were admitted to hospital for 20 days. For 10 days fluid balance was maintained and no diuretics given. During the next 10 days, a gram of frusemide was given orally, with fluid and electrolyte replacement based on the 24-hour urine collections which were made throughout the 20-day period. Daily estimations of sodium, potassium, urea, creatinine and osmolality were made on plasma and urine. The excretion of water (p < 0.01), sodium (p < 0.01) and potassium (p < 0.05) increased significantly during the treatment period. There was no significant change in blood pressure, weight, creatinine clearance (C/CR), clearance of urea (C/Urea), total urea and creatinine excretion, serum sodium, potassium or osmolality. The results demonstrate that a gram of frusemide, administered to patients in stable chronic renal failure, does not have any effect on intrinsic renal function. However, there was a significant increase in urine volume, as well as sodium and potassium excretion.