Astrocytic reaction to various types of pre- and perinatal damage in the brain was studied using the immunohistochemical method for glial fibrillary acidic protein. The reactive gliosis could be detected as early as 20 weeks gestation. Reactive proliferation of the astrocytes could be seen already at 4 days after the insult. In addition to reacting to focal lesions, the astrocytes also proliferated diffusely throughout the white matter. The diffuse proliferation is the most significant finding in the evaluation of the perinatal damage, in both the acute state and in the long-term survivors.