Two basic different strategies for surfactant treatment of respiratory distress syndrome have emerged: prophylactic, or preventilatory, treatment at or shortly after birth versus rescue treatment after the initiation of mechanical ventilation in instances of clinically confirmed respiratory distress syndrome. Although treatment at birth has the theoretic advantage of delivering surfactant more uniformly to the airways before mechanical ventilation, it has the disadvantages of delaying physiologic stabilization after birth and resulting in unnecessary treatment, at considerable cost, of 20 percent to 40 percent of infants born at or less than 30 weeks of gestation. Rescue therapy permits early physiologic stabilization and confirmation of respiratory distress syndrome, but with the theoretic disadvantages of early lung injury from mechanical ventilation in the surfactant-deficient lung and less uniform surfactant distribution. Previous comparative trials have been biased by incomplete study enrollment and inclusion of infants in preventilation treatment groups without evidence of surfactant deficiency or immaturity. In addition, outcomes have varied in placebo-treated infants.