BACKGORUND: inhalation anesthetics have been known as bronchodilators, and there are reports that enflurane has some relaxing effects on tracheal smooth muscles. However, there are not so many reports on the ACh release in the postganglion nerve endings. We tried to evaluate the effect of enflurane on the contraction of the tracheal smooth muscle in the postganglion nerve ending in guinea pigs. METHODS:isolated tracheal preparations of guinea pigs were used and contractions were induced by electrical field stimulation (3 Hz