Endocrine cells in the gastrointestinal tract of the domestic duck were identified immunocytochemically using antisera specific to bombesin, chromogranin A, cholecystokinin (CCK), gastrin, glucagon, neuron specific enolase (NSE), neurotensin, secretin, 5-hydroxytryptamine (5-HT), somatostatin, substance P and vasoactive intestinal polypeptide (VIP). Chromogranin A, 5-HT and somatostatin immunoreactive cells were widespread throughout the gastrointestinal tract. Bombesin immunoreactive cells were observed only in the proventriculus and the gizzard. CCK, substance P and neurotensin immunoreactive cells were present in the intestinal tracts from the duodenum to the colorectum. The latter were numerous also in the antrum. Gastrin cells were peculiar to the antrum but present also in the gizzard and small intestine. Glucagon immunoreactive cells were present in the jejunum-ileum and above all in the large intestine. Only few secretin cells were present in the duodenum. The highest frequency of endocrine cells was found in the antrum, while the lowest was observed in the caeca. Antisera to somatostatin and substance P showed numerous nerve cells and fibers besides endocrine cells, whereas NSE and VIP immunopositivity was found in the nervous structures only of the gut wall.