Amniotic fluid surface active material was measured by the foam stability test (FST) in 102 high-risk pregnancies within 24 hours of delivery. There was no linear correlation between the FST and gestational age in the 106 preterm infants studied. The incidence of respiratory distress syndrome (RDS), however, was significantly related to the FST. The case fatality rate (CFR) was not significantly related to the FST. The CFR was significantly related to low five-minute Apgar score (≤5), suggesting that the events prior to delivery contributed toward this increased mortality rate. RDS also occurred in immature infants with positive FST and good Apgar scores, which indicates that immaturity is an independent variable in the pathogenesis of RDS. Our study supports the conclusion that three factors are of prime importance in the pathogenesis and outcome of RDS: surfactant deficiency, intrapartum complications, and immaturity.