Twenty-seven infants with respiratory distress and hypoxemia of noncardiac etiology were treated with tolazoline. Thirteen infants had hyaline membrane disease and 14 had respiratory distress attributable to causes other than hyaline membrane disease. An immediate response to tolazoline, a rise in Pao2of 15 torr or more within 15 min, was seen in 11 infants in the hyaline membrane disease group and in eight infants of the other group. Six infants in the hyaline membrane disease group and 11 infants in the second group survived. Tolazoline should be considered as a therapeutic adjunct in the management of hypoxemia which persists after optimal homeostatic and ventilatory support.