By using light and electron microscopic cytochemical technique, the activities and distributions of AP isoenzymes in gastric cancers and benign gastric diseases were examined. The results showed: Nagao, Regan and Kasahara isoenzym~, which were not expressed in normal gastric mucosae and non- malignant lesions, might be considered as tmnor markers of gastric conccr; The epithelimn of intestinal metaplasia exhibited intestinal- type AP only, which was one of the markers of well - differentiated intestinal metaplusia. In the view - point of the gene expression of AP isoenzymes, two mutation hypothesis and recessive - gene mutation hypothesis might be fit for gastric cancer.