1 The role of the sympathetic innervation of cerebral arteries remains controversial. Therefore, the functional activity of the adrenergic innervation of the rabbit basilar artery was characterized and compared to that of a peripheral artery, the ear artery. 2 Both the ear artery and basilar artery have similar endogenous noradrenaline (NA) contents but accumulation of [3H]-NA was considerably greater in the basilar artery. 3 Studies of tritium efflux after loading with [3H]-NA demonstrated a considerable non-neuronal component since neither guanethidine nor tetrodotoxin completely blocked tritium efflux during nerve stimulation. Pretreatment with blockers of uptake2 did not eliminate this problem. 4 Comparison of methods for estimating the functional activity of adrenergic nerves showed that, for the vessels studied, NA content and [3H]-NA accumulation gave markedly different answers. Fractional release of [3H]-NA did not correspond to fractional release of endogenous NA. 5 Adrenergic nerves innervating cerebral arteries are shown to have a high activity relative to a peripheral artery. While cerebrovascular sympathetic innervation may not play an important role in normal circumstances, its influence may be seen in pathological conditions.