The effects of CPAP and CNEP on lung mechanics and lung volumes were investigated in a group of 12 healthy newborn infants. Both resulted in a mild suppression of respiration. The fall in TPR50 was far greater during CPAP than during CNEP. Both led to a one third fall in dynamic compliance. Approximately 50% of the distending pressure was transmitted to the mediastinal structures whether applied as CPAP or CNEP.