Diuretics have been used as one of therapeutics for acute respiratory failure. We observed the change of arterial blood gases at the same ventilatory level, after intravenous injection of 20 mg of furosemide, in ten of twenty patients without diseases of heart, lung or kidney. The obtained results were: 1) 30 minutes and 1 hour after the injection of furosemide, there were peak increments in arterial PO₂. 2) There were no significant changes in pH and PaCO₂.