✓ A method for intraoperative evaluation of the hemodynamic state in patients with carotid-cavernous fistula is described. Electromagnetic flow probes were applied on the internal carotid artery (ICA) in the neck and on the intracranial part of the artery distal to the fistula in five patients. Fistula “steal5 ranged from 90 to 975 ml/min. Forward flow rate in the intracranial portion of the ICA, distal to the fistula, was from 40 to 170 ml/min. The reverse flow rate during test occlusion of the ICA in the neck was between 35 and 60 ml/min. The ratio reverse flow/forward flow is assumed to give an indication of the collateral capacity of the cerebral vasculature and of the tolerance to trap ligation of the ICA. The pulsatile pattern of the intracranial ICA flow in this series varied considerably, and this parameter is also found to be of importance in the evaluation of the capacity of the collateral arterial system. The monitoring of cervical ICA flow proved to be a reliable way to supervise the procedure of plugging the fistula with flow-carried muscle emboli in conjunction with trap ligation.