Doppler transcranial ultrasonography (TCD) is a very useful method of identification and monitoring of vascular contraction in patients with subarachnoid bleeding. The method is noninvasive and relatively cheap and may be applied at the bedside whatever the patient's condition. It requires considerable experience and skill on behalf of the person administering it, however. This article discusses the difficulties involved in proper diagnosis of vessel contraction by means of TCD and in differentiating between vessel contraction and other conditions involving increased bloodflow. The article also reviews the latest criteria for identification of contraction of particular brain base arteries. Daily TCN examinations of patients with SAH help to assess the contraction properly and to identify patients in whom the risk of neurological deficit is particularly pronounced. They also help to monitor the effectiveness of treatment. Finally, TCN may help in the optimal timing of the angiography and possible surgery of the aneurysm.