The present study documents the occurrence of renal failure in 4 nephrotic patients including 3 with minor glomerular lesions and one with membranoproliferative glomerulonephritis. One patient died of sepsis at 3 months after onset of the acute renal failure. In the remaining 3, forced diuresis employing albumin plus furosemide in increasing doses to 600 mg/day reversed the renal failure independent of corticosteroid therapy. All of the 4 patients showed characteristic findings consisting of a remarkably low fractional excretion of sodium and an unexpectedly low urine osmolality at the onset of acute renal failure, although they were rather hypervolemic. Our findings suggest that the occurrence of a low fractional excretion of sodium and low osmolality may provide a good index of an absolute indication for intensive weight reduction therapy such as high-dose furosemide in nephrotic patients with acute renal failure in order to reverse the acute renal failure.