The author investigated the blood flow in the common carotid arteries by means of Doppler ultrasonography in 98 patients after stroke. An UDP 10 ultrasound flow detector was used and the results obtained in patients dying during the treatment were compared with those who were discharged improved. In the cases with lethal outcome considerable (over 30%) asymmetry of blood flow was found, usually but not always with slowing of this flow on the side of the lesion. Diastolic blood flow was in this group significantly lower on the side of the cerebral lesion and compared with the group with favourable outcome. Other differences were not characteristic. The results of these investigations showed that in patients with a high-grade asymmetry of blood flow in the common carotid arteries and impairment of brain perfusion evidenced by slowing down of the diastolic blood flow the course of the stroke is often more severe. This may be of prognostic significance.