The modern classification of the gastroenteropancreatic endocrine system (GEPES) is presented. Qualitative and quantitative composition of the entero-endocrine system (EES) included in the GEPES is considered, as well as functional role of every type of the cells. The literature data are summarized and the morphology at the light optic and electron microscopic levels of the endocrine cells and the peptidergic nerves of the intestine is demonstrated. The existing methods for investigation of the EES endocrine cells and for the whole neuroendocrine complex of the gastro-intestinal tract taken together are analysed.