Equine pancreas was investigated with immunohistochemical methods to study the distribution of endocrine cells immunoreactive to anti-insulin, anti-glucagon, and anti-somatostatin. A-cells demonstrable by anti-glucagon are located in the center of Langerhans islets and frequently in the duct epithelium. Few A-cells are seen associated to acini. Anti-insulin reactive B-cells form a large zone around the center of the Langerhans islets in which some B-cells lie between exocrine cells and others, although few, are located in the duct epithelium. D-cells stained with anti-somatostatin serum form a discontinuous outermost zone around the Langerhans islets. In some islets the D-cells are also observed among the B-cells or between the border of A- and B-cells. Single D-cells are seen in the duct epithelium or between acinar cells. In younger horses, endocrine cells are more frequently associated in bulges of the duct system. The histotopographic relation between these endocrine cell types is discussed with respect to its functional significance.