Teleological significance of the pressence of beta adrenergic receptors in blood vessels of skeletal muscle seems to be in redistributing blood flow from viscera to skeletal muscle when muscular activity is required or anticipated. Adrenaline secreted from the adrenal medulla in such occasions constricts blood vessels in viscera as its alpha effect and dilates blood vessels in muscle as its beta effect. The latter effect is considered to be especially important in the rat which lacks cholinergic vasodilator fibers.