The distribution of endocrine cells in the human intestine was studied by immunostaining using the labeled avidinbiotin technique. The total number of endocrine cells was abundant in the proximal portion of the small intestine and the distal portion of the large intestine. Gastrin, cholecystokinin, and motilin immunoreactive cells were localized in the proximal portion of the small intestine. Peptide YY, serotonin, and glucagon/glicentin immunoreactive cells were distributed more abundantly in the lower large intestine. The serotonin and somatostatin concentrations in the colonic mucosa determined by high-performance liquid chromatography and radioimmunoassay were higher in the distal than proximal portion of the large intestine, being in correlation with the distribution of serotonin and somatostatin immunoreactive cells estimated by immunostaining. Therefore, the regional differences in the number of endocrine cells and the mucosal concentrations of the hormones probably reflect differences in the physiological functions of different regions of the gut. Not many endocrine cells with unknown peptides and animes and immature endocrine cells were present in the lower large intestine. Therefore, the frequent occurrence of carcinoids in the rectum is difficult to explain by the quantitative dominance of endocrine cells alone in the rectal mucosa, and other factors are considered to need evaluation
