To further elucidate the pathophysiological role of peptide hormones in duodenal ulcer (DU) disease, several endocrine, paracrine and neurocrine peptides were determined radioimmunologically in biopsies of gastroduodenal mucosa obtained endoscopically in 8 subjects without upper gastrointestinal disease, and in 8 duodenal ulcer patients. The DU patients had a BAO of 6.6 +/- 1.9 and a PAO of 41.8 +/- 6.1 mEq/h. In DU patients, a lack of the acid and gastrin-release inhibiting agent somatostatin was found neither in antral nor in fundic mucosa (185 +/- 60 vs 83 +/- 19 pmol/g tissue wet weight in controls). Basal and peak acid outputs of DU patients were positively correlated with fundic somatostatin concentrations (p less than 0.01). While gastrin levels were not significantly elevated in the antrum of DU patients, the mucosal content of potentially releasable gastrin of the duodenal bulb and the descending duodenum was higher than in controls (p less than 0.01). In the whole duodenum, CCK-like immunoreactivity was also more abundant in DU patients than in controls, whereas GIP and motilin did not exhibit characteristic profiles. Presumably as a reactive phenomenon, the mucosal levels of the peptidergic neurotransmitters VIP and substance P were markedly increased in the proximal duodenum of DU patients.