Changes in cuff pressure and volume of tracheal tubes were studied in 60 patients undergoing lower abdominal surgery under general anaesthesia with nitrous oxide and oxygen as the anaesthetic gas mixture. The cuffs were inflated with either anaesthetic gas mixture or air. Three different brands of tubes were used. The pressure in the air filled cuffs increased steadily throughout the procedure and reached level high enough to impede microcirculation in the tracheal mucosa within one hour. We conclude that filling the cuff with anaesthetic gas mixture is a simple and reliable way to achieve stable cuff pressure during anaesthesia.