At 4 years of age, two groups of prematurely born children were compared in relation to physical, mental, and behavioral development—24 children who had been afflicted with neonatal respiratory distress syndrome (RDS) and 53 who had not. Those who had suffered from RDS had been treated with urokinase-activated human plasmin or received placebo; oxygen was administered only for relief of cyanosis, the maximum concentration being 38%. Statistical evaluation did not show a significant difference in development between the RDS and control groups. A significant negative correlation was found, however, between birth weight and degree of disability. These findings seem to indicate that RDS does not increase the handicaps associated with prematurity. Chest roentgenograms revealed possible pulmonary fibrosis in only one child who had survived RDS.