The gastric anatomic-functional behaviour (gastric acid secretion, gastrinemia parietal cell mass, histological pattern of the fundic mucosa) was evaluated in 50 duodenal ulcer patients in the active stage of the disease. After 28 days of treatment with cimetidine (1 g/day), the 42 healed patients stopped therapy completely for three months. At the end of the follow-up the anatomic-functional behaviour was monitored and compared with the initial data in the 24 subjects who were still symptomless, as well as in the 18 patients whose duodenal ulcer relapsed. The analysis of the data obtained demonstrated that gastric acid secretion, gastrinemia and morphology of the fundic mucosa do not vary with the different activity phase of duodenal ulcer; therefore additional factors, and in particular alterations of mucosa resistance, are presumed to be responsible for the development of ulcerous lesions. Moreover, a comparison between the initial data of patients with ulcer healing after cimetidine therapy, and of those with unhealed ulcer, failed to reveal any significant differences, thus denying a prognostic value of acid secretion tests in duodenal ulcer disease.