Objective The method transcranial Doppler (TCD)and end-tidal carbon dioxide partial pressure (ETCO2 ) was used to investigate the cerebrovascular reserve capacity in patients with intracranial artery stenosis.Including the cerebral vasodilator reserve,contracted reserve and the overall reserve.Methods The 72 cases were enrolled in this study,include of 42 patients with one or two sides middle cerebral artery (MCA) stenosis,or other intracranial artery stenosis and 30 normal persons. All the patients were routinely examined with TCD,and the TCD QL software was used to evaluate the cerebrovascular reserve. Hypercapnia was induced by inhaling the CO2 who breathed himself,and hypocapnia was induced by voluntary hyperventilation. The changes of velocities were recorded in both side of MCA,and the ETCO2 was recorded by the external measuring device. Results ( 1 ) The cerebral vasodilator reserve of one side of MCA stenosis group ( ( 3.65% ± 2. 62% )/mm Hg),the heavier side of multi-vessel stenosis group ( ( 1.99% ± 2. 78% )/mm Hg ),and normal control group ( left ( 3.54% ± 1.66% )/ mm Hg; right (3. 81% ± 1.63% )/mm Hg) had significant difference( F = 3. 755 ,P ＜ 0. 05 ). The heavier side of multivessel stenosis group' s cerebral vasodilator reserve were significantly lower than normal control group ( t =- 2. 546,P ＜ 0. 05 ). (2) The overall reserve of one side of MCA stenosis group ( ( 3.22% ± 1. 27% )/mm Hg),the heavier side of multi-vessel stenosis group( (2. 30% ± 1.14% )/mm Hg),and normal control group(left (3. 19% ±0. 81% )/mm Hg;right (3. 23% ±0. 70% )/mm Hg)had significant difference(F=5. 894,P ＜0. 01 ). The heavier side of multi-vessel stenosis group' s overall reserve were significantly lower than normal control group( t = - 3. 357,P ＜ 0. 01 ) and they were also significantly lower than one side of MCA stenosis group (t = 2.471,P ＜ 0. 05 ). (3) The extent of vascular disease correlated inveresely to the cerebral vasodilator reserve( r = - 0. 322,P ＜ 0. 05 ) and the overall reserve( r = - 0. 364,P ＜ 0. 05 ) in the heavier side of patients who have vascular disease.Conclusions ( 1 ) TCD with ETCO2 is a simple,economic and effective method for assessing CVR. (2)The capacity of cerebrovascular reserve was reduced in patients with intracranial artery stenosis.