Microscopical studies were performed on the infiltration of mononuclear cells in the interstitum adjacent to cancer. It was examined whether the extent of the cellular infiltration had some correlation to the titer of humoral antibody and immunoelectrophoretic pattern in sera from each patient. 1. No significanct correlation was obtained in the extent of the cellular ifiltration and the development of gastric cancer. 2. The extents of the infiltration were proportional to the titers of humoral anti body by Boyden's hemagglutination test. 3. There was no relationship between the extent of the infiltration and the immunoelectrophoretic pattern. These data would seem to suggest that human gastric cancer has some homograftic aspects in the immunological point of view.