It is well known that cuff overinflation in endotracheal tubes may cause serious damage to the tracheal mucosa. Cuff overinflation is also related to the diffusion of nitrous oxide across the cuff membrane, thus giving way to a progressive volume/pressure increase up to overcoming, critical capillaric perfusion pressure. The kinetics of hi-lo cuff-pressure in single-lumen endotracheal tubes during general anesthesia using nitrous oxide has been well documented. The authors have investigated the cuff-pressure modifications in 40 left double-lumen tubes (DLTs), monitoring the inflation pressure for both the endotracheal and endobronchial cuffs at the sealing of the airways and at different phases of the anesthetic procedures performed using nitrous oxide, in 40 male patients undergoing thoracic surgery. In ten of these case, special equipment was used in order to keep the cuff-pressures steady and at the lowest sealing level. The pressure shows the same trend in both cuffs but, depending on the medium calibre of the main left bronchus and the volume/pressure relations of the endobronchial cuffs, the pressure in the latter increases faster. The investigation was performed using an original equipment developed by the authors; such equipment is able not only to monitor the cuff-pressures, but also to maintain them at steady controlled levels (below 20 cm water seal), by means of counterregulating all the volume variations due either to anesthetic requirements, or to the diffusion of nitrous oxide.(ABSTRACT TRUNCATED AT 250 WORDS)