The author has determined pepsin in the chronic gastritis by Bucher, Grossman, Ivy method and compared with it in the other stomach diseases. 1) The fasting pepsin level; 87.3 P. U.(Hb) in the gastric ulcer, 54.8 P. U.(Hb) in the stomach cancer, 102.0 P. U.(Hb) in the gastric ulcer, and 183.6 P. U.(Hb) (the highest in all) in the duodenal ulcer. Pepsin has been proved even in the case of achlorhydria in the chronic gastritis. 2) Gastric secretion by the use of its stimilants (Histamine, Insulin, Vagostigmin, Caffeine, and dried bonito extract) increased in the pepsin level in every case, and was marked especially by the vagus stimulant. Pepsin level was considerably elevated in some of the hypochlorhydria in the chronic gastritis and especially by the vagus stimulant. Acidity and pepsin level, in general, went side by side on the use of the stimulants excepting histamine, and those relation was definite in the caffeine and in the dried bonito extract. The elevation of the pepsin level was much higher than that of the acidity, in insulin and in vagostigmin.