OBJECTIVE: To investigate the effect of endothel in and endothelin A receptors (ETAR) on regional cerebral blood flow after traum atic brain injury (TBI). METHODS: The changes of endothelin-1 (ET-1) content with radi oimmunoassay, mRNA expression and the location of ETAR with in situ hybridizatio n, and the function and effect of antagonist BQ123 on regional cerebral blood fl ow (rCBF) through intracisternal application were dynamically observed on 130 ad ult rabbits after TBI. RESULTS: ET-1 increased significantly in regional brain tissue s, and the expression of ETAR mRNA increased apparently and predominantly distri buted in the cerebromicrovascular endothelium after trauma. The rCBF declined si gnificantly, but by using selective ETAR antagonist BQ123 to treat the rabbits, the decrease of rCBF could be apparently prevented. CONCLUSIONS: It demonstrates that ET-1 may primarily contribut e to the rCBF decrease after TBI, while providing that the role of ET-1 is medi ated through ETAR.