Ketamine hydrochlaride, chemically related to both pencyclidine and cyclohexamine, is a new nonbarbiturate intravenous anesthetic agent. Clinical investigations were begun in 1965 by Domino and associates, who first used the term "dissociative anesthesia" . Anesthesia induced by ketamine dissimilar to that resulting from the more widely used intravenous or gaseous componds. Because of its minimal depressant effect on the cardiovascular and respiratory systems as well as its dissociative effect on the central nervous system ketamne bas achieved widespread use. However there have been few reports on its effect an intestinal motility. The present study was undertaken to determine the effect of ketamine on doudenal motility and on other smooth muscles of the rabbit. Strips of various isolated smooth muscle, 2 cm long from adult rabbits weighing about 2 kg, were suspended in a muscle chamber containing Tyrode's solution, which was bubbled with oxygen gas, and the solution was kept constant at 38C. Contraction of the preparations was recorded on polygraph (Grass, mode17). After being washed several times with fresh solution, the smooth muscle strips attained constant motility and tonus. Ketamine and other drugs were added in various concentrations to the chamber. The results areas follows: 1) Ketamine relaxed the isolated rabbit duodenag strip and potentiated the relaxing effect of epinephrine, norepinephrine and isoproterenol. 2) The relaxing effect of ketamine on isolated duodenal strip of rabbits was not abolished by the adrenergic blocking agents, but ketamine antagonized histamine or serotonin-induced contra ction. 3) Ketamine did not exert any effect on the isolated auricle, aorta, trachea, trigone and detrusor muscle strips of rabbit. From the results described above, it may be concluded that ketamine exerts a depressant effect on the isolated duodenal smooth muscle of rabbits without relation to adrenergic receptors.