Histochemical studies of five hydrolytic enzymes, i. e. alkaline phosphatase, acid phosphatase, beta esterase, beta-glucuronidase, and leucine aminopeptidase and eight dehydrogenases, i. e. lactic, succinic, malic, alpha-glycerophosphate, glutamic, beta-hydroxybutyric, glucose-6-phosphate, and isocitric dehydrogenase were carried out in the gastric cancers removed from 100 patients. Enzyme activities were compared with the histological features of stomach cancers in each patient and the grade of its advancement. Histological analysis of stomach cancer was followed by the classification established in 1962 by the Japanese Pathological Society. And the grade of advancement was judged by the criteria eatablished by the Japanese Reserch Society for Gastric Cancer. As a whole, the poorer differentiated cancer cells showed the weaker enzyme activites than the well differentiated ones. However, no correlations were observed between enzyme activities and the grade of infiltration by cancer cells. Generally enzyme activities of carcinoma simplex were weaker than those of adenocarcinom and scirrhous carcinoma showed slightlly weaker activity than carcinoma simplex. According to the classification of Borrmann, enzyme activites of infiltrative types were weaker than those in localized types. Lactic dehydrogenase showed the strongest staining intensity in all of the enzymes. The activity was observed in hydrolytic enzymes of carcinoma cells in the following desending order: beta-glucuronidase, beta-esterase, acid phosphatase, leucine aminopeptidase and alkaline phosphatase, while in that of stromal elements : beta-glucuronidase, acid phospbaase, beta-esterase, alkaline phosphatase and leucine aminopeptidase. The activity of dehydrogenases of carcinoma cells was in the following desending order: lactic, malic, glucose-6-phoshate, isocitric, succinic, alpha-glycerophosphate, glutamic and beta-hydroxybutyric dehydrogenase, and in that of stromal elements : lactic, malic, succinic, alpha-glycerophosphate which was similar to glutamic, beta-hydroxybutyric similar to glucose-6-phosphate and isocitric dehydrogenase. There was a tendency that the cancer tissues obtained from the patients of more advanced stage showed the stronger activity of enzymes than that of early stage ones.