Systematic ultrasonic Doppler flow examinations of 98 migraine patients during a headache free interval revealed a highly significant reduction of blood flow in the A. supratrochlearis, an endbranch of the A. ophthalmica, compared with a control group (n=55). 34 migraineurs with invariable hemicrania showed a significant reduction of ophthalmica-blood-flow on the affected side, compared with the painfree side. Doppler flow examinations during spontaneous migraine attacks revealed a characteristical increase of the flow velocity in Aa. carotides communes, internae, externae and Aa. vertebrales, whereas the A. ophthalmica showed a flow reduction during the attack. Of 6 patients suffering from cluster headache, there was a marked flow acceleration in the A. ophthalmica during spontaneous or nitrolingual provoked attacks. The results indicate that the noninvasive transcutaneous Doppler sonography is of value in the differential diagnosis of migraine patients and cluster headache. The implications of the results are discussed with respect to the hemodynamics of migraine and cluster headache.