The internal carotid arteries were evaluated with Doppler ultrasound technique in patients with acute cerebrovascular disease. The results of the Doppler examination of 325 vessels were compared to presence of carotid bruits on auscultation. In 126 arteries the findings were also compared with those on aortocervical, single carotid or post-mortal angiography. The Doppler flow reaction was normal in 74% of the vessels, uncertain in 20% and pathologic in 6%. The sensitivity of the Doppler assessment in finding stenosis of more than 75% lumen diameter reduction was 85% with a specificity of 94%. The specificity increased with higher degree of vascular stenosis. Carotid bruits were heard in 34 arteries. The sensitivity of auscultation in detecting stenosis 75% was 47% with a specificity of 83%. The sensitivity fell with higher degree of stenosis. The Doppler procedure is a valuable tool in detecting haemodynamically significant stenoses in the internal carotid artery. The method could serve the following purposes in the clinical situation: 1. Screening procedure for further investigations in TIA and minor stroke patients fit enough to be candidates for vascular surgery. 2. Before blood-pressure can be safely reduced in patients with cerebrovascular disease. 3. For evaluation of the arteriosclerotic process in stroke-patients thereby improving prognostication.