We examined 30 children with gastrointestinal pathology aged 7-15 years. The examined patients were divided into two main groups: group 1 included 12 patients with duodenal ulcer during an exacerbation, group 2 included 8 patients with duodenal ulcer without exacerbation and in the control group there were 10 children hospitalized with functional dyspepsia. An increase in acid-forming function was observed in two main groups, while it was significantly higher in the group of children with duodenal ulcer during an exacerbation.