In a retrospective study, ultrasonic Doppler findings obtained with directional continuous wave equipment were evaluated in 51 patients in whom subsequently the diagnosis of an internal carotid artery occlusion was confirmed by angiography or autopsy. The evaluation was based on the registration of mean velocity analogues of medial frontal (supratrochlear) and common carotid artery blood flow. Patients referred for stroke 3 weeks or less before the Doppler examination were considered acute; the remaining patients were considered having long-standing carotid artery occlusion. There was flow reversal in the medial frontal artery in 80% of the acute, and in 62% of the chronic group. The percentage of "no flow" curves in the 2 groups were 20 and 21% respectively. Among the chronic patients 18% showed a physiological direction of medial frontal artery flow, but extremely low streaming velocity. There was a linear correlation between the medial frontal artery flow velocities and the side differences of flow velocity in the common carotid arteries in both groups indicating that, with high cross-flow between carotid arteries, reversed medial frontal artery flow is less important. The impact of both the cross-flow between the carotid arteries, and the vertebral basilar collateral on medial frontal artery flow was demonstrated by analyzing angiographical data. Physiological flow direction in the medial frontal artery can be preserved even with a deficient inter-carotid cross-flow if, in addition to internal carotid occlusion, the patient also has an external carotid occlusion on the contralateral side.