Aim To investigate the relationship of adrenomedullin and its mRNA with the focal cerebral ischemia/reperfusion injury and hypertension in rats. Methods The experimental hypertension rats were prepared by the advanced Kellen's methods.The models of middle cerebral artery occlusion in rats were constructed by the line-block-method,and after ischemia for 2 h they were reperfused.By using the immunohistochemical method,the percentage of adrenomedullin positive cells both in hypertension group and nonhypertension group after focal cerebral ischemia /reperfusion was determined and compared,and the expression of adrenomedullin mRNA in the brain tissue after focal cerebral ischemia/reperfusion in rats was monitored by the RT-PCR analysis. Results Adrenomedullin mRNA expressed in the normal rats' brains,and it increased slightly in the sham operated group,but it had no significant difference from the normal group(p<0.05).The over-expression of ADM mRNA existed after cerebral ischemia/reperfusion in rats,which had significant difference with the normal group and the sham operated group(p<0.05 both).After focal cerebral ischemia /reperfusion in rats,adrenomedullin mRNA in not only the ipsilateral but also the contralateral side of the ischemic area expressed high,especially in the ischemic area(p<0.05). The adrenomedullin positive cells expressed in the brain tissue of the rats in the normal group and the sham operated group,and their percentages were 2.87%±0.78% versus 2.47%±0.59%,both of which had no significant difference(p<0.05). The adrenomedullin positive cells expressed high in the non-hypertension group after ischemia /reperfusion,especially in the ischemic side,whose percentage of the positive cells was 59.42%±3.71%,and the contralateral side was also significant,whose percentage of the positive cells was 36.87%±5.28%,and the differences between them was significant(p<0.05),which was also significantly different from the sham operated group and the normal group(p<0.05). By comparing the percentage of the adrenomedullin positive cells in the hypertension group with that in the non-hypertension group,the percentages of the adrenomedullin positive cells in the hypertension group(78.60%±4.82% in the ipsilateral side of the ischemic area and 57.52%±5.22% in the contralateral side) were much higher than the non-hypertension group(p<0.05). Conclusions Adrenomedullin and its mRNA express high after the cerebral ischemia/reperfusion,and the over-expression is much more significant.Adrenomedullin has relation to the cerebral ischemia/reperfusion injury,and also to the vascular endotheliocyte injury after hypertension.