The distribution and numbers of G cells and of parietal cells were related to the distribution and severity of histopathological alterations (inflammatory cell infiltration, atrophy and intestinal metaplasia) in corresponding mucosal tissue blocks from resected stomachs (12 patients with gastric ulcer, 11 with duodenal ulcer, and 14 with duodenal ulcer and uremia). In all patients the histopathological features were more severe in the pyloric antrum than in the body, and the change in severity corresponded well with the disapperance of G cells at the body-antrum border. The transitional body-antrum zone was histopathologically similar to the remaining antrum. A marked individual heterogeneity of the histopathological alterations was observed. An increasing grade of atrophy was associated with increased severity of inflammation, and the presence of intestinal metaplasia was especially associated with atrophy. No significant correlation was found between the antral G-cell number and the grade of antral inflammatory cell infiltration, whereas there was a reduction in cell number with increasing grade of atrophy in all patient categories. The parietal-cell density in the body mucosa was decreased with increasing grade of inflammation as well as with increasing grade of atrophy. The presence of patchy intestinal metaplasia resulted in a complete absence of G cells and of parietal cells from the corresponding part of the mucosa in the antrum and body respectively.