Investigated as a potentially more effective modality of therapy, fast neutron radiation is a kind of high linear energy transfer irradiation (LET) and its relative biological effectiveness (RBE) is higher compared with other low-LET radiations.However, the injury of radiation itself is progressive and deteriorative, and the related pathogenesis mechanism remains to be explained.Since apoptosis occurs after fast neutron radiation in certain cell populations of tissues, we have detected the level of tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and its death receptor DR5 in rat cortex, hippocampus, striatum and cerebellum after whole-body radiation at different time postradiation.The results show that TRAIL level is up-regulated at 7th day but decreases almost to the normal level at 14th day in the four brain regions, while DR5 expression increases significantly after 14 day in rat cortex, hippocampus and striatum, except in cerebellum, where the DR5 level seems to decrease from lth day to 14th day post-radiation.As we know, TRAIL can bind to DR5, and then activate the apoptosis pathway, causing cell death.The up-regulation of DR5 level may indicate the progressive injury of central nervous system, and the phenomena, which the expression of DR5 behaves in cerebellum is different from the other three brain regions, may reflect some other injury mechanisms.Further study still needs to be done to illustrate the pathogenesis of delayed cell death in various brain regions.