Arterial diameter, blood velocity and blood flow of both common carotid arteries were studied in 24 patients with isolated unilateral internal carotid artery stenosis, without any other significant lesion of the carotid system. The methodology used a pulsed Doppler system with two original characteristics: an adjustable range-gated system and a double transducer probe enabling both the arterial diameter and blood velocity to be evaluated. On the involved side, the diameter, the blood velocity and the blood flow were significantly reduced (p less than 0.001) in comparison with the opposite side. The degree of the internal carotid artery stenosis judged on arteriography was negatively correlated with (i) the blood flow of the common carotid artery homolateral to the stenosis (r = -0.78, p less than 0.001); and (ii) the ratio of the common carotid artery blood flow between the involved and the opposite side (r = -0.80, p less than 0.001). The proposed quantitative evaluation can be suitable for the detection and for the follow up of patients with stenosis of the internal carotid artery who do not have any other lesion of the carotid system.