The aim of this study was the development of a simple bedside test to assess cerebrovascular reserve capacity using transcranial Doppler sonography. We tried to validate the increase in blood flow velocity as cerebrovascular reserve capacity in 20 (3 normal, 7 TIA, 10 completed stroke) patients. They were studied using transcranial Doppler sonography and rCBF SPECT before and after injection of 1 g acetazolamide. Their increases in blood flow velocity and changes in cerebral blood flow correlated significantly in the symptomatic hemispheres (p less than 0.001). Blood flow velocity between the two hemispheres (symptomatic and asymptomatic) was not significantly different at rest. We offer these simple and reliable methods in clinical studies to clarify the frequency of ischemic stroke of hemodynamic origin.