Interest in the Doppler ultrasound phenomenon of "High Intensity Transient Signals" (HITS) is based on the, thus far, unproven hypothesis, that these signals may to some extent represent silent cerebral microembolism ahead of a TIA/stroke and hence identify patients at risk for stroke. We prospectively investigated 80 patients with 102 moderate/severe internal carotid artery lesions. Patients with additional potential sources of cerebral ischemia were excluded. Bilateral transcranial Doppler monitorings of the middle cerebral arteries (MCA) were performed for =>30 min. HITS occurred more often in patients with completed stroke (21.9%) than in patients with transient ischemic deficits (12.5%), but significantly less in asymptomatic subjects (4.3%) (p<0.05). The incidence was maximal in patients examined within the first week after the onset of stroke. HITS were significantly more often associated with severe (> 70%) (23.5%) than with moderate (50 - 70%) internal carotid artery stenosis (3.4%) (p<0.05). These figures are closely related to annual stroke risk estimates recently reported about patients evaluated in multi-centre trials for carotid endarterectomy, and support the concept that HITS associated with carotid disease represent an important individual risk predictor.