Background: Scientists have been dealing with the search and elaboration of radio protective factors since the middle of the previous century. One of the radio protective factors is the xenogenic cerebrospinal fluid. Materal and methods: The article is devoted to revealing and studying the morphological changes of the rats’ bone marrow after parenteral injection of xenogenic cerebrospinal fluid (CSF) in different periods of postnatal development (newborn, immature, mature). Lactating cows aged 4-6 years were used as CSF donors. The effect of SCF was studied by electronic microscopy histological methods. Results: In the article some results of the experiment on the influence of the xenogenic cerebrospinal fluid (XCSF) on the structure of the irradiated bone marrow of Wistar rats are shown. The evident radio protective effect was proved by the analyses of the destructive processes degree in red bone marrow cells of the rats exposed to total body radiation at 5 Gr and 3- and 10-times infusions of XCSF. Conclusions: Findings testify to activating processes of regeneration of all sprouts of red marrow at the correction of consequences of irradiation by introduction of CSF. However the least degree of these processes manifestation is observed in the old age group, that is CSF, probably, with the decline of the activity of adaptation mechanisms.