Ten newborn babies with severe respiratory distress syndrome, all dependent on artificial ventilation, were treated via the airways with the isolated phospholipid fraction of bovine or porcine surfactant. After treatment with surfactant at a median age of 10.5 h, there was in all patients a striking improvement of lung aeration in chest films, with a decrease in parenchymal fluid retention and in distension of bronchioli. These radiologic findings were associated with a dramatic improvement of oxygenation and a significant reduction of the right-to-left shunt. In spite of the rapid therapeutic response, four patients died from cerebral hemorrhage. One of the surviving patients developed bronchopulmonary dysplasia. Our findings document efficacy of this new surfactant preparation in the neonatal respiratory distress syndrome, but the long-term effects need to be further tested in randomized clinical trials.