The protein-like materials of gastric juice consists of many kinds of non-heat precipitated mucous materials. By means of the quantitative analysis of the tyrosine levels contained in these materials and the isolated tyrosine level of gastric juice, the resolution of protein in cancer patients has been examined. In the case of the quantitative analysis of the tyrosine in total dissolved mucin and isolated tyrosine using trichlor acetic acid filtrate of gastric juice which was gathered after the subcutaneous injection of histamin, the tyrosine levels in total dissolved mucin in the cases of gastric cancer, gastric ulcer and gastritis were almost all the same. The isolated tyrosine levels in the cases of ulcer and gastritis, however, were 2-11 mg%, while that in the case of the gastric cancer was 9-26 mg%. It means the increase of isolated amino acid in gastric juice of cancer patients. According to Glass, Boyd and so forth, dissolved mucin was classified into mucoprotein and mucoproteose, and quantified the tyrosine levels of each of them. In the case of gastric cancer the tyrosine level of mucoprotein evidently decreased, but that of mucoproteose increased rather than that in the case of ulcer and gastritis. On the other hand the secretory volme of gastric juice showed clear decrease in patients with cancer. Consequently the tyrosine level of secretory mucoprotein (the tyrosine level of mucoprotein mg% × the secretory volume cc.) markedly decreased in the case of gastric cancer in comparison with the cases of ulcer and gastritis: that is, in the cases of gastric cancer the average level was 19 mg. in half an hour and 5 mg in 30 to 60 minutes after histamin injection, while in the cases of ulcer and gastritis the average levels were 201 mg and 107 mg respectively. The tyrosine levels of secretory mucoproteose did not show so clear distinction as that of mucoprotein Then fifteen cases of gastric cancer were classified into the following four groups. hydrochloric acid the tyrosine level of mucoprotein Group I (1 case) (+) normal Group II (3 cases) (-) normal Group III (7 cases) (-) decrease Group IV (4 cases) (-) little and impossible to quantitative analysis Comparing with clinical appearance, the anemia level was the highest in the group IV, which was followed by the group III, that of the group II was the lowest, and no anemia was noticed in the group I. In the view-points of the growth of cancer and indication of gastric resection, radical operations were possible in all the cases of group I, II and in the 4 cases of group III. On the other hand only the exploratory laparotomy was performed in the remaining 3 cases of group III and all the cases of group IV. According to Glass, Boyd, Rubinstein and so forth, mucoprotein is secreted from so-called “mucoid cells” in the neck of gastric gland, and it is similar to Castle's intrinsic factor from the physical and physiological points of view. We often become aware in daily clinical experiences that the degree of anemia is often higher in the case of cancer of stomack than the other viscera such as breast, lung, esophagus, colon, rectum, and so forth. Therefore the deficiency of gastric mucoprotein may be related to the anemia level in gastric cancer patients.