The morphological changes of gastric mucosa taken from different areas has been studied in patients of approximately the same age with achlorhydria, extreme hypochlorhydria and normochlorhydria. The serum gastrin level and parietal cell antibodies were determined in the achlorhydric parietal cell antibodies were determined in the achlorhydric patients. In the latter the diffuse gastritis was localized in the corpus-fundic area, while the changes in the antral region were few and occurred mostly in the superficial zone. In normochlorhydric patients however, the diffuse gastritis was localized in the antral region, with only few changes at the corpus-fundic area. In patients with extreme hypochlorhydira either the fundic or the antral region was involved. Besides the diffuse gastritis intestinal metaplasia, pseudopyloric metaplasia, and atrophy of mucosa were also observed, although much less commonly. The increase of gastrin level could not be related to a definite morphological pattern in the gastric mucosa. It can be assumed that each of the two types of gastritis has a different natural history; the antral site of gastrititis cannot be transformed into the fundic site, nor can the fundic site be transformed into the antral site.