56 stroke patients were investigated with the new non-invasive method of transcranial Doppler sonography (TCD), operating with a range-gated pulsed 2 MHz Doppler. In 28,6% of the 56 patients TCD provided additional information about the status of the basal cerebral arteries. The results of the TCD investigation were confirmed by angiography in 14 patients. This result indicates that TCD is a valuable non-invasive method of high accuracy for the detection of intracranial brain artery diseases and collateral flow mechanisms.