To examine flowdynamic change after superficial temporal artery (STA)-middle cerebral artery (MCA) bypass surgery, we measured the pulsatility index (PI) and end-diastolic blood flow velocity (Vd) of the donor STA by percutaneous direct microvascular Doppler sonography. In 63 patients (5-76 y/o) who had received STA-MCA bypass surgery for either ischemic stroke (11 cases), supportive therapy before parent artery occlusion in the treatment of internal carotid giant aneurysm (3 cases), or moyamoya disease (49 cases) (total 96 sides of STA), PI was 1.01±0.41 and Vd was 18.9±8.4 cm/sec. When compared to normal volunteers (6-76 y/o, 70 sides of STA) (PI: 1.96±0.63 and Vd: 5.6±2.5 cm/sec), PI decreased and Vd increased after STA-MCA bypass with high statistical significance (p<0.0001 and p<0.0001, respectively). Low PI and high Vd indicate that STA flow has changed from extracranial flow to intracranial flow. STA flowdynamics can be quantitatively assessed by measuring PI and Vd of the donor STA. This new bedside method is easy, noninvasive and useful to identify functional patency of the STA-MCA bypass.