A population of 8 children aged 7 to 13 and radiologically and/or endoscopically diagnosed of duodenal ulcer is compared with another made up of 12 normal children of similar ages and weights. In both groups gastric secretion, basal and after pentagastrin stimulation, and serum levels of gastrin and pepsinogen I, basal and after pentagastrin stimulation, and serum levels of gastrin and pepsinogen pepsinogen basal and after pentagastrin stimulation, and serum levels of gastrin and pepsinogen I, basal and after proteic meal, were studied. BAO, MAO and PAO were significantly higher in ulcer patients. Gastrinemia, both basal and stimulated, were rather similar in both groups. Serum pepsinogen I was always higher in ulcer patients in the basal state than in their healthy counterparts (greater than ng/ml vs. 30-50 ng/ml), but was not modified by proteic meal in either group. The fact that all ulcer children had a familial history and a basal pepsinogen I elevated, aside with the secretory response to stimulation, suggests that ulcer can be result either of an increased mass or of a higher sensitivity of gastric parietal cells that could be related to genetic factors.