Introduction Headache may be the commonest complaint heard in physicians' offices. The great majority of headaches are linked either with cranial vasodilatation or skeletal muscle contraction and cranial vasoconstriction. The former are called migraine; the latter, muscle-contraction headache.1 Changes in gastric function, feeling state, nasal function, fluid and electrolyte excretion, cardiac rhythm, and body temperature regulation may occur in association with headache Fig. 1.—Cranial artery pulse wave recorder. attack. A part of our newer knowledge of migraine headache phenomenology is herein reviewed. Fig. 2.—Poser slit lamp and camera attachment for study of bulbar conjunctival vessels. Headache mechanisms were studied with use of the devices shown in Figures 1 and 2. Fig. 3.—Effect of topical acetylcholine on bulbar conjunctival vessels. Contrast the normal vessels at the top with the minimal dilatation (sensitivity) at bottom. Fig. 4.—Effect of topical levarterenol on bulbar conjunctival vessels. Those at the top are normal. At