After the patients were intubated with a low-or high-pressure cuff, the cuffs were inflated with air enough to seal the trachea. Intracuff volume and pressure were measured and the pressure exerted on the trachea were calculated. After administration of 0%, 50%, or 67% nitrous oxide the measurements were eompared with the initial values. 1) At the start the high-pressure cuff exerted a higher pressure on the trachea than the low-pressure cuff. 2) The volumes of the high-pressure cuffs were not increased after 2 hours by the increasing the coneentration of nitrous oxide, but the pressures in the cuffs were increased significantly. Volumes and pressures of low-pressure cuffs increased after 2 hours when increasing the concentration of nitrous oxide.3) The pressure exerted on the traches by the high-pressure cuff decreased without a relationship to the concentration of the nitrous oxide, but the pressure exerted on the trachea by the low-pressure cuff increased with increased concentration of nitrous oxide.