The previous report showed that the specific activity of Lactic dehydrogenase was significantly elevated in gastric juice of chronic gastritis and gastric cancer. In addition, the possibility was proposed that chronic inflammation of gastric mucosa in both disorders might have contributed to the elevation of activity. In the present work, isoenzymatic studies were performed with electrophoresis and histochemical examination in order to elucidate the origin of the LDH activity found in gastric juice. LDH isozymes of human gastric juice are characterized by predominance of LD(I) and a gradual decrease of activities towards the cathode, showing no difference in patterns among normal controls and various gastric disorders, such as chronic gastritis, gastric ulcer and gastric cancer. The results indicate that the origin of LDH activity of gastric juice is identical, and locate at some specific mucosal cell or cells. Histochemical studies were performed in order to spot the locali ation of LDH in gastric mucosa at cytological level. According to Kaplan's report, chicken heart muscle LDH (mostly H type) was stable, whereas skeletal muscle (mostly M type) lasts its activity when exposed to 55℃ for 10 minutes. Thus gastric mucosal frozen sections mounted on slides were incubated at 55℃ for 10 minutes, and then histochemically stained. LDH activity was found to remain in parietal cells alone. It is suggested from the above experiment that LDH in parietal cell is mostly of H type, and LDH in other cells (mucosal epithelial cells, chief cells, intestinal metaplasia and other cells) mostly of M type, and that LDH in gastric juice is probably derived from gastric mucosal cells other than parietal cells. Many invastigators have histochemically shown an increased LDH activity in mucosal epithelial cells in chronic in-flammation and in intestinal metaplasia. It is known however that the numbers of parietal cells and chief cells are decreased in chronic inflammation. Consequently the elevated LDH activity of gastric juice in chronic gastritis and gastric juice in chronic gastritis and gastric cancer is thought to be from mucosal epithelum and intestinal metaplasia.