The characteristics of gastric mucosal patterns in the polyp-bearing stomach were investigated by the endoscopic Congo red test and systemic four-points biopsy in 46 patients with hyperplastic polyps and 21 patients with gastric adenomas. In addition, function of the stomach in these patients was assessed by determination of gastric acidity and fasting serum gastrin level and by gastrin response test to a beef extract. In the investigation of the gastric mucosal pattern in hyperplastic polyp patients, Type A gastritis (involving the corpus but sparing the antrum) was most frequently found. On the other hand, extensive intestinal metaplasia from the pyloric antrum to the corpus was most often noted in the adenoma-bearing stomach. Hypergastrinemia was more marked in hyperplastic polyp patients, and may be involved in the pathogenesis of hyperplastic polyps. Attention should be paid to the detection of cancer in areas without polyps during endoscopic observation and reexamination of patients. On these occasions, the characteristics of the background mucosa for each type of polyp should be kept in mind.