Amidated gastrin-17 is a biologically and physiologically important molecule among the family of the gastrin peptides. Amidated gastrin-17 is the most powerful gastrin peptide in the feedback control mechanism of the acid secretion and output from the parietal cells in the gastric corpus. This peptideis solely synthetized and secreted into the circulation by the so called G cells (“gastrin cells”) in the gastric antrum. A positive immunohistochemical reaction for gastrin-17 is a sign of a highly differentiated gastrin-secreting cell and normal antral mucosa. In atrophic gastritis, the normal antral (pyloric) glands and gastrin-17 synthetizing cells disappear. Metaplastic pyloric glands (pseudopyloric metaplasia) do not contain immunopositive gastrin-17 cells.