OBJECTIVE: To explore the effect of dexamethason e by local treatment on cerebral edema and brain damage after brain injury. METHODS: Twenty-two rabbits were classified into 2 groups, Gro up A (the control group, n=11) and Group B (the treated gr oup, n=11). An rabbit brain contusion model was made by bo ne windowplasty by extradural hitting. Group B was treated by local infiltrating and spraying of dexamethasone at equidistance to lesions. Group A was given nor mal saline in the same way as Group B. The changes of moisture in brain tissues and serum myelin basic protein (MBP) were observed. RESULTS: The percentage of water content in damaged hemisphere in Group A and Group B was 81.75%plus minus0.56% and 79.45%plus minus0.52% respe ctively. There was a significant difference between the 2 groups (P<0.05). The normal level of MBP was 1.66 mug/Lplus minus0.71 mug/L, while the value of MBP in Group A and Group B were 5.98 mug/Lplus minus2.08 mug /L and 3.15 mug/Lplus minus1.09 mug/L separately. The level of MBP in Group A an d Group B were higher than normal level and there was also a significant differe nce between Group A and Group B (P<0.05). CONCLUSIONS: The results of our study showed that the brain moi sture and MBP in serum were increased after brain injury while reduced after tre atment with dexamethasone. It is demonstrated that local treatment of brain inju ry with dexamethasone has an obvious therapeutic effect on cerebral edema and se rum MBP.