The frequency and distribution of 11 endocrine cell populations were studied in the intestine of differently aged buffalo, grouped on the basis of diet: 2-d-olds (suckling), 5-mo-olds (weaning) and 5-y-olds (ruminant adult diet). The endocrine cell populations were identified immunocytochemically using antisera against 5-hydroxytryptamine (5-HT), somatostatin, gastrin, cholecystokinin (CCK), COOH-terminal octapeptide of gastrin/CCK, neurotensin, motilin, gastric inhibitory polypeptide (GIP), secretin, glucagon/glicentin (GLU/GLI) and polypeptide YY (PYY). In adult buffalos the regional distribution of endocrine cells is similar to that of other adult ruminants. During postnatal development, these cell types showed the following changes in their frequency and distribution: (1) 5-HT, neurotensin and gastrin/CCK immunoreactive cells (i.c.) showed a decrease in frequency with age; (2) somatostatin i.c. frequency remained stable with age; (3) motilin, GIP, secretin and CCK i.c. showed a slight increase in frequency with age; (4) GLU/GLI and PYY i.c. decreased in frequency with age in the small intestine, caecum and proximal colon and an increase in frequency in the rectum. It was hypothesised that the endocrine cell types, whose presence and localisation is substantially stable in all examined ages, probably contain substances that are strictly necessary for intestinal function. In contrast the hormones contained in the cell populations that decreased with age, are probably involved in physiological needs during the milk and weaning diet or play a role in intestinal growth.