Chief cell mass and type I serum pepsinogen (PGI) were calculated in 19 advanced antral gastric cancer of intestinal type. Comparisons were also made with parietal cell mass and acid secretion. In gastric cancer of the antrum there is a significant decrease of the chief cell mass and of serum pepsinogen I. The patients were subdivided according to the histological findings of the fundic mucosa. In cases of antral gastric cancer with superficial fundic gastritis there is normozymogenism with hyperpepsinogenemy; with preatrophic fundic gastritis there is hypozymogenism with normopepsinogenemy; with atrophic fundic gastritis there is hypozymogenism with hypopepsinogenemy. Similar behavior of the chief cell mass between antral gastric cancer and fundic atrophic gastritis without cancer has become recognized and while the validity of PGI as a marker of fundic atrophic gastritis has emerged it does not allow discrimination between atrophic fundic gastritis and atrophic fundic gastritis associated with gastric cancer of the antrum.