In this thesis the detection of atherosclerotic disease of the extracranial carotid arteries using continuous wave ultrasound is studied. The pathophysiology, natural history and treatment of carotid artery disease and its importance as a cause of stroke are described. Methods of investigation other than by ultrasound eg arteriograms, carotid phonoangiography, oculoplethysmography with their inability to identify mild degrees of stenosis and other drawbacks are discussed.