Morphological methods were used to study several segments of the rat's brain after gamma-irradiation by 10, 20, 50 and 100 cSv. Tissue samples were investigated shortly after dose delivery, in 24 hours, and after 6, 12, 18 and 24 months since irradiation. Neurons were shown to be sensitive to radiation. Conventionally, the nervous system reaction can be segmented into three stages, i.e. an early response (initial 30 days), revealed changes (by mo. 6) and repair. Life span of irradiated animals was not altered; however, individual morphological variations and even incomplete repair may affect quality of life of radiation disaster fighters and population of contaminated regions.