Both clinical and physiological consideration of migraine suggests that the pathophysiology of the syndrome is intimately linked to the trigeminal innervation of the cranial vessels, the trigeminovascular system. Studies were conducted on cats and humans to examine the interaction of these systems with the effective acute antimigraine drugs dihydroergotamine and sumatriptan. In the animal studies cats were anesthetized and prepared for routine physiological monitoring as well as for blood sampling from the external jugular veins. Cerebral blood flow was monitored continuously using laser Doppler flowmetry and the effect of trigeminal ganglion stimulation on both cerebral blood flow and jugular vein peptide levels determined prior to and after administration of either sumatriptan or dihydroergotamine. Stimulation of the trigeminal ganglion led to a frequency-dependent increase in cerebral blood flow, with a mean maximum of 43 ± 9% at a stimulus frequency of 20 per second. There was a marked reduction in these responses by some 50% after administration of either sumatriptan or dihydroergotamine. Trigeminal ganglion stimulation at a frequency of 5 per second also led to a release into the cranial circulation of calcitonin gene–related peptide (CGRP), with the level rising from 67 ± 3 to 82 ± 5 pmol/liter on the side of stimulation. These increases were also markedly antagonized by both sumatriptan and dihydroergotamine. Human studies were conducted as part of the overall evaluation of sumatriptan for the treatment of acute migraine. In 7 of 8 patients responding to subcutaneous sumatriptan administration, elevated CGRP levels (60 ± 8 pmol/liter) were normalized, with the headache being relieved (40 ± 8 pmol/liter). These data characterize some aspects of the cerebrovascular physiology of the trigeminovascular system and demonstrate important interactions between this system and the effective antimigraine agents sumatriptan and dihydroergotamine and that such interactions can be represented in animal models.