The immediate response to intravenous administration of nikethamide was studied in 15 patients with acute respiratory failure. Clinically, there was noticeable increase in mental lucidity and respiratory drive. Laboratory studies revealed varied degrees of arterial pCO2 decrease and improvement in minute ventilation and oxyhemoglobin saturation. Further hypoventilation induced by oxygen breathing was also corrected by nikethamide. The average effective single intravenous dose varied between 5 and 8 ml. Additional amounts by slow intravenous drip could further sustain the effects of the primary dose. Toxic effects were minimal and brief; ratio between therapeutic and toxic levels was good.