Evidence is presented that somatostatin-containing cells are present in the gastro-intestinal tract of the dog. Thus immuno-fluorescent cells were detected by the use of antiserum to cyclic somatostatin. These cells were mainly encountered in the antral mucosa and in the neighbourhood of gastrin-producing cells. No cross reaction was observed between gastrin and somatostatin. It is suggested that locally produced somatostatin controls gastrin secretion, and, more generally, that somatostatin-containing cells, multifocally distributed, modulates secretion of a large number of glands.