Various rates of development are characteristic for particular structures of the human central nervous system (CNS). The differences of the maturing brain steam and telencephalon are evident in routine neuropathological examination. The fetal and postnatal archi- and neocortex also reveals uneven levels of maturation. In order to precisely describe those differences in humans we performed a morphological and morphometric study on the dorsal vagal nucleus of the medulla oblongata, on Ammon's horn and on neocortex from midgestation to the 18th postnatal month. The numerical density of neurones, cell perikarya andnuclear cross-sectional area, and the ratio of nucleus to perikaryon area were measured. The results demonstrate a development-dependent decrease in cell density and progressive differentiation of neurones according to their changing size. They express a process of maturation which differs in rate across the CNS structures examined.