AbstratThe numbers of immunoreactive gastrin and somatostatin cells in gastric and duodenal mucosal biopsy specimens from dyspeptic patients with duodenal ulcers and dyspeptic controls without ulcers were calculated using a morphometric method. The levels of gastrin and somatostatin in the tissue were also measured by the radioimmunoassay. The results showed no significant difference in the number of G cells and the level of gastrin in the tissue between the ulcer and non‐ulcer groups. However, the number of D cells and the level of somatostatin in the tissue in ulcer patients were remarkably reduced in comparison with those in non‐ulcer patients (P<0.01 andP<0.05, respectively). The G: D cells and gastrin: somatostatin ratios in ulcer patients were much higher than those in the non‐ulcer control group. It is considered that the reduction of D cells and the relative lack of somatostatin in duodenal ulcer patients might have a role in the mechanism of the duodenal ulcer