Chorioamnionitis is frequently associated with preterm deliveries before 30 weeks gestation. Chorioamnionitis correlates both with an increased risk of bronchopulmonary dysplasia and with a decreased risk of respiratory distress syndrome. Both interleukin-1alpha and endotoxin can induce inflammation in the fetal lungs and lung maturation after preterm birth when given by intra-amniotic injection. Inflammation can also result in an arrest of alveolarization, and this lung developmental abnormality is prominent in the lungs of preterm infants that die of bronchopulmonary dysplasia. The mechanisms by which infection/inflammation can have both beneficial and injurious effects on the preterm lung remain to be characterized.