Goal and objectives of the study was comparative description and establishment of dose-time dependence of changes in permeability of the hemato-encephalic barrier (HEB) in phylogenetically different parts of the brain cortex, i.e. new (Fr2 and Cg3), old (hippocampal fields CA1-CA4 and dentate fascia) and paleocortex (piriform cortex) following exposure to 0.1; 0.2; 0.5 and 1 Gy of ionizing radiation (dose rate = 50 cGy). Dependence of microvessels permeability on dose, post-exposure time and cortex phylogenetic age was established. Changes in brain microvessels, in the phylogenetically young cortex in particular, produced by 0.5 Gy and 1 Gy remained uncompensated till the end of investigation. Pronounced changes persisted over the period of one year after radiation exposure; complete recovery was not observed even in the phylogenetically old cortex.