Changes of volume and pressure due to N2O-diffusion into PVC and Latex cuffs of endotracheal tubes were measured. Endotracheal tubes with a small-volume cuff (Magill and Portex) and one type of a large-volume, low-pressure cuff (Lanz) were examined. Within 48 h significant changes of volume and pressure were registered at different starting volumes and different N2O-concentrations. In the small-volume cuffs of the Portex and Magill tubes very high pressures were always noted; increases of volume were always seen, which were accompanied by increases, in some cases also by decreases of pressure. In the large-volume cuffs of the Lanz tube there were increases of volume and pressure; the measured pressures where however, in a clinical unimportant range. These changes are caused by N2O-diffusion into the cuff, slowed N2-diffusion out of the cuff, prestretching of the cuff membrane by the starting volume and further stretching by N2O diffusing into the cuff. These measurements are of practical clinical significance: This high-pressures due to starting volume and N2O-diffusion in small-volume cuffs explains the higher rate of trauma to the trachea, even after short term intubation, in contrast to the extremely low pressures in large-volume, low-pressure cuffs.