We are aware that a continuous negative pressure may be obtained with the Air-Shields incubator-respirator without the use of an override switch. The method suggested by Outer-bridge, et al. was used on the two machines we have but produced maximum pressures of only 3 to 5 cm of water. It is possible to modify the expiratory vacuum control to produce higher pressures. However, if the highest pressure obtainable is only 15 cm of water this would be inadequate since we have had two infants who required higher pressures.