A simplified method of determining dynamic respiratory compliance (C dyn) in the newborn is described. Studies were performed during mechanical ventilation on 24 infants with respiratory distress syndrome (RDS) and 6 infants without RDS. Cdyn was evaluated at pressure settinghs of 20/0, 25/5 and 30/10 cm H2O. Significant decreases (p < 0.05) in Cdyn were noted with each increase in end-expiratory pressure setting. The values for Cdyn in RDS patients obtained by this method closely approximated previously published data for lung compliance in babies with RDS. This simple and reproducible method may be useful in following the course of illness in infants with RDS.