The validity of different non-invasive methods of detecting extracranial arterial disease is assessed in a large series of more than 20 000 patients studied using CW-Doppler (indirect and direct techniques) and more than 2000 patients studied by a newly developed ultrasound Duplex system. While CW-Doppler analysis still represents the method of choice for the evaluation of various degrees of carotid obstructions causing more than 50 per cent lumen narrowing (overall accuracy 99 per cent), the technically far more complex and expensive Duplex systems should be used for the diagnosis of normal arterial vessels versus minor plaques, and in particular for the detection of ulcerative lesions representing possible sources of cerebral embolism. Furthermore, simultaneous flow-volume and velocity-pattern analysis across the arterial lumen provides new insight into the cerebral blood flow, thus promising acquisition, for the first time, of rapid changing parameters in the cerebral circulation.