Retinal artery pressure was measured by ophthalmodynamometry in 15 patients with occlusion of the internal carotid artery in its extracranial part. Nine of the patients had severe neurological deficit whereas the remaining six had slight or intermittent symptoms. Retinal artery pressure was reduced on the side of the internal carotid artery occlusion in all patients studied. Near-zero low diastolic retinal artery pressure on the affected side was a common finding among patients with severe deficit and was also seen in some patients with slight deficit. Its presence strongly suggests occlusion of the ipsilateral internal carotid artery.