Twelve rhesus monkeys were delivered prematurely at 129, 130, or 131 days. The first breath was inhibited while tracheotomy was performed and a catheter introduced into the umbilical artery. Into the tracheal tubes of six of the newborn monkeys was instilled 0.20 to 0.27 ml. of a natural surfactant (SA) suspension, obtained from lung wash of adult rabbits. Nothing was given to six control monkeys. Breathing was then supported with a ventilator. Although its settings were adjusted in attempts to maintain normal blood gases, the control monkeys developed severe hypercapnia and acidosis, and two died after 4 1/2 and 5 1/2 hours. The remaining four control monkeys and the six treated monkeys were killed after six hours. Pulmonary pressure-volume characteristics were conspicuously better following SA treatment. It was concluded that instillation of SA in the upper airways of premature primates prior to their first breath holds promise as an effective way of preventing respiratory distress.