The authors provide the data obtained during examination of 36 children with celiac disease and 18 children with lactase deficiency. The children's age ranged from 8 months to 15 years. All the children underwent spot biopsy of the gastric and duodenal mucosa followed by immunomorphological PAP-staining of the biopsy specimens and count of the number of gastrin- and somatostatin-producing cells. Gastrin in the blood serum was measured by radioimmunoassay. The children with celiac disease manifested an increase of the number of somatostatin-producing cells in the duodenum and decrease of their number in the pyloric part of the stomach, seen in the acute phase of the disease. The number of gastrin-producing cells remained unchanged. The level of gastrin declined in the acute phase and increased during a remission. The alterations described were found to be related to the atrophic processes in the small intestinal mucosa. In lactase deficiency, no significant alterations were established in the number of pyloric and duodenal endocrine cells or in blood gastrin level.