To elicit Transcranial doppler (TCD) potentialities in asymptomatic hemodynamically significant occlusive carotid diseases, twenty one patients with subclinical severe stenosis (more than 50%) of internal carotid artery (ICA) have been studied. After routine TCD, bilateral embolic monitoring of middle cerebral arteries (MCA) has been carried out. Besides, the functional test with breath-holding for cerebrovascular reserve (CVR) was made in all the patients. Control group consisted of 18 healthy volunteers without any ICA abnormality. The results of the study reveal that CVR--the index of brain circulation autoregulation safety--is more exact marker of its stability than a degree of extracranial carotid stenosis. TCD embolic monitoring of MCA enables not only to diagnose brain embolism but to elicit the embolic source origin (arterio-arterial or cardial). Thus, both TCD with breath-holding and TCD embolic monitoring facilitate identification of patients at high risk of ischemic events, which is important for brain ischemic disease prophylaxis.