Kaike Hot Spring is situated at the seaside, in the western part of Tottori Prefecture, Japan. In chemical composition it contains 9.3 g. of salts per kilogram of spring water and may be classified as a common salt spring. The author examined the effect of the drinking of Kaike spring water on gastric acidity in 21 patients. a) Two hundred m!. of this spring water were given to 10 patients by stomach tube at 37℃. The gastric acidity of the patients was measured at 30-minute intervals for a period of 105 minutes following the administration of the spring water. In 3 cases of normal acidity and 6 cases of hyperacidiy, the spring water appeared to inhibit the secretion of gastric acid, compared with the effect of the caffein control water. b) Two hundred m!. of the spring water diluted two-fold with tap water were given to 11 patients. In two cases of normal acidity and two cases of hypoacidity, on significant difference was observed between the effects of the spring water and those of the control water. In all 7 cases of hyperacidity, however, the spring water observably depressed the acid secretion of the stomach, as compared with the effect of the control water. On the basis of these results, the author concludes that it is advisable to use the spring water diluted two-fold with tap water for the purpose of treating gastric disorders.