Recently, duplex sonography has been used as a screening test for the evaluation of carotid arterial disease. If an occlusion of atherosclerosis is located at the bifurcation of the lower portion of the internal carotid artery, the luminal change may be directly visualized on high-resolution B-mode sonography or color-Doppler images. But when the lesion is located at the high cervical, petrous or cavernous protion of the internal carotid artery, it is difficult to directly visualize the lesion with the sonography. The purpose of this paper is to evaluate the indirect changes on the Doppler patterns of both common carotid arteries with clamping of an internal carotid artery. Thirty common carotid arteries in fifteen normal rabbits were examined with duplex ultrasonography using high-resolution real-time imaging and 7.5MHz pused-wave Doppler flow measurements with velocity waveform analysis. Systolic velocity (SV) was 45.4$pm$ 8.4cm/sec, end-diastolic velocity (EDV) 15.3$pm$4.9cm/sec and resistative index(RI) 0.66$pm$ 0.08 in the common carotid artery before clamping of the internal carotid artery, SV was 26.3$pm$7.8cm/sec, EDV 6.0$pm$5.2cm/sec and RI 0.78$pm$0.18 in the ipsilateral common carotid artery and SV was 56.6$pm$13.0cm/sec, EDV 22.3$pm$8.2cm. sec and RI 0.61$pm$0.10 in the contralateral common carotid artery after clamping of the internal carotid artery. During clamping of the internal carotid artery, the difference between SV of bilateral common carotid arteries was 30.3$pm$13.8cm/sec and EDV 16.3$pm$9.2cm/sec. there was no difference of the velocity patterns of the common carotid artery between preclamping and declamping of the internal carotid artery. In conclusion, lower SV and EDV in a comon carotid artery than that in contralateral side on Doppler patterns strongly suggests an occlusion of ipsilateral internal carotid artery.