Many investigations concerning the effect of vestibular stimulation on the movement of the digestive organs had been made by means of the balloon method, X-ray, etc.. The author investigated the effect of vestibular stimulation on the movement of the dog's stomach by using the electromyogram (EMG) of the smooth muscle. The electrodes were inserted into the subserosal layer of the antrum of the stomach according to Prof. Takeda's method (Chief of the Department of Surgery, Osaka Univerity). The following four different kinds of stimula- tions were used. 1. Irrigation of the external auditory canal with 100cc of 0-C water.2. Pendular rotation with amplitude of 90degrees and period of 2 seconds for 3 to 5 minutes.3. Direction-fixed rotation with angular velo-city of 360 degrees per seconds for 5 minutes.4. Vertical movement (up and down, 40 times/min., amplitude 35cm, maximal acceleration 0.13G)for 30 minutes.Since the vertical movement exerted the most remarkable effect on EMG of the stomach among the above-mentioned four kinds of stimulations, it was used in most of the following experiments.The results obtained were as follows:1. During the vertical movement of normal dog, the discharge intervals were markedly prolo-nged and fluctuated irregularly. The prolongation of the discharge intervals gradually disappeared on the cessation of the movement, and the discha-rge intervals returned to the normal condition in about 60 minutes.2. In the bilaterally labyrinthectomized dogs, and in those which were pre-treated with intrave-nous injection of sodium bicarbonate, the changes of the discharge intervals did not occur during the vertical movement.Consequently, it was found that the prolonga-tion and the fluctuation of the discharge intervals of EMG of the dog's stomach were caused by labyrinthine stimulation, and that those EMG changes could be prevented by the injection of sodium bicarbonate.