The postnatal development of the zonation and the glial cells of the median eminence (EM) was investigated in male rats. On the 1st day of life, the ME is mostly undifferentiated. In contrast to adult animals, only the ependymal, subependymal and palisade layer can be observed. The remaining area is almost unorganized. A more distinct zonation of the EM exists about the 10th day of life. Ependymal and subependymal layer are reduced to a monolayer of cells; in addition, the reticular layer appears. The adult structure of the EM is seen for the first time about the 14th day of life. The development of the zonation of the EM is finished at the 3rd week of life. Mature microglial cells occur in the median eminence at the 1st day of live. Ependymal cells, tanycytes and astrocytic tanycytes (Zaborszky and Schiebler 1978), which can be found in a greatter amount as an individual cell type, are relatively immature. Protoplasmatic astrocytes occur at the 4th, and fibrous astrocytes at the 14th day of life. The development of glial cells may be finished at the end of the 4th week of life together with the maturation of oligodendrocytes. The opening of the 3rd ventricle needs 2 weeks, that of the recessus infundibularis is finished after the 3rd week of live. On the basis of their lipid granules and the synaptic contacts with neurosecretory axons it is presumed that the tanycytic and astrocytic tanycytes have regulatory functions in connection with neurosecretory processes.