Loop diuretics (furosemide, bumetanide, muzolimine, piretamide, torasemide) are powerful drugs capable of increasing sodium excretion and urine output even when renal function is markedly impaired. In patients with chronic renal failure (CRF), loop diuretics may be given to control extracellular volume (ECV) expansion responsible for hypertension. But the use of loop diuretics in chronic uremia is mostly helpful when impaired renal function co-exists with nephrotic syndrome or chronic heart failure. Due to their powerful natriuretic activity, loop diuretics have been administered also to patients on maintenance dialysis to reduce the frequency of and/or to curtail dialysis time. In this condition, however, the increase of sodium and water excretion is very limited; whereas the use of diuretics in high dosage is not devoid of risky side effects such as neurologic lesions, cramps, deafness, weakness, muscle pain. In some patients with oliguric form of acute renal failure (ARF), loop diuretics increase sodium excretion and urine output. They do not affect the mortality rate for ARF but may facilitate the treatment of patients by reverting an oliguric form to a non-oliguric form of ARF.