Ischemia in the carotid artery territory due to atherosclerotic stenosis of the innominate artery is rare. We report a case in which transcranial Doppler ultrasonography (TCD) and SPECT with acetazolamide challenge proved the hemodynamic mechanism. The patient presented with three hypotensive TIAs in the right middle cerebral artery territory. Angiography showed a tight innominate artery stenosis and subclavian steal but no coexistent carotid or vertebrobasilar lesion. SPECT showed disturbed regional blood flow in the middle cerebral artery territory along with an exhausted perfusion reserve capacity. After angioplasty, flow velocities were normal and the perfusion reserve was restored. SPECT should be used to select patients at risk susceptible to benefit from angioplasty.