In order to improve the treatment of functional disorders with result from the clinical radiotherapy of encephalic diseases with rotate head γ knife,the pathological changes and expression of TNF—α and IL—1β mRNA in the right caudate nucleus of the rat brain irradiated locally with a single dose of 200Gy γ rays were studied by general and electron microscopical observation and in situ hybridization respectively. The results showed that the pathological changes develop through 4 stages: (1) cerebral edema (0—14 days after irradiation) ; (2) necrosis of the injured tissue (21d — 2 months); (3) scavenging of the necrotic tissue (3 — 6 months) and (4)hyperplasia stage (9 —12 months). It was also found that the permeability of the blood —brain barrier began to increase 2 hours after irradiation,and the degree of increase showed a positive correlation with the survival period of the animals. The ultrastructural changes in endotheliocytes and the gliocytes occurred prior to that of neurons. In this study,the expression of TNF—α and IL —1β mRNA was found increased in irradiated brain tissue, and treatment of rats with dexamethasone before irradiation could inhibit this expression.