The effect of central renin-angiotensin system (RAS) on one-kidney Grollman hypertension during the maintaining phase and its mechanism were investigated in rats. The arterial blood pressure (ABP) and the content of angiotensin II (A II) and norepinephrine (NE) in brain regions was measured respectively. 4 weeks after operation the ABP was elevated significantly, and it sustained at high level 8 weeks post-operatively. However, ABP in the control group underwent no significant changes at the same period. The A II and the NE content in the brain regions of the operated group were significantly higher than in those of the age-matched control group. During the maintaining phase of hypertension captopril (150 micrograms/10 microliters) was injected into the lateral cerebroventricle at 0.5 h, 1.0 h and 1.5 h respectively, and ABP and content of A II and NE were determined at the corresponding time. The results showed that the above three parameters decreased consistently at 0.5 h and 1.0 h, and increased gradually at 1.5 h, suggesting that the central RAS might play an important role in the maintaining phase of one-kidney Grollman hypertension in rats.