With enzyme histochemical methods, regional differences were observed regarding the connexions of the tanycyte processes and certain cytoplasmatic of the tanycytes reactions in the ependyma of the infundibular and infra-mammillary recesses of the albino rat. (1) According to the G„PD and TPND methods, the basal processes of the tanycyte ependyma exhibit a definite vascular contact only dorsally from the n. periventricularis arcuatus. Ependymal fibre endings can be seen in the region of the sulcus tuberoinfundibularis and in the inframammillary recess on the basal surface. Medially from the former, the tanycyte processes can be followed into the zona externa of the infundibulum. A convincing tissular connexion with the hypophysis portal system and with the cells of the pars infundibularis adenohypophyseos cannot be observed. (2) The TPPase activity usual in the secretory nervous system structures is missing from the tanycyte ependyma. The ependyma of the caudal end of the inframammillary recess exhibits isolated intense alkaline phosphatase activity. Rostrally from this, in the ependyma of the top of the inframammillary recess, there are more intense enzyme reactions than in the ciliated ependyma elsewhere lining the third ventricle.