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. C(dyn) was evaluated at pressure settings of 20/0, 25/5 and 30/10 cm H2O. Significant decreases (p<0.05) in C(dyn) were noted with each increase in end-expiratory pressure setting. The values for C(dyn) 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.