Seven children born prematurely who survived the respiratory distress syndrome, seven children born prematurely who had no neonatal lung disease, and seven normal children born at term were studied by comparison of flow volume curves obtained while breathing air to those obtained while breathing 80% helium and 20% oxygen. Expiratory flow rates in air both groups of prematurely born children were lower than flow rates of the children born at term, and the volumes of iso-flow were higher in the survivors of RDS than those of the children born at term. The differences in flow rates in air suggest an increase in large airway resistance in both groups of prematurely born children. It is speculated that this may be secondary to growth retardation related to prematurity. The elevated Viso V in the RDS group suggests an increase in small airway resistance secondary to the disease or to its therapy.