AbstractSeveral gastrointestinal peptides with proven or suggested endocrine or paracrine functions influence gastric acid secretion, gastrointestinal motility, and mucosal blood flow. Increased or decreased release of such factors could participate in the pathogenesis of duodenal ulcer disease by inducing increased gastric acid concentration in the duodenal bulb. To date, increased stimulation of parietal cells by gastrin has been demonstrated only in patients with gastrinoma, G‐cell hyperplasia, gastric outlet obstruction, hyperparathyroidism, excluded antrum, and short bowel syndrome, but not in the usual duodenal ulcer disease. Also, a defective inhibition of parietal cell function by endocrine or paracrine factors, such as gastric inhibitory polypeptide, secretin, somatostatin and vasoactive intestinal polypeptide, seems not to exist in patients with duodenal ulcer disease. However, as long as the physiology of gastrointestinal peptides in gastric secretion and motility is not understood, a possible role of these factors in the pathogenesis of simple duodenal ulcer disease cannot be excluded.