The innervation of the femoral artery and vein in the dog was studied using: a) glyoxylic acid fluorescence (for the histochemical localization of adrenergic nerve fibers); b) acetylcholinesterase (for the histochemical localization of cholinergic nerve fibers). -Andrenergic nerve fibers and related terminals in both vessels are confined to the adventitial-medial transitional zone and the outer layers of the media. Acetylcholinesterase containing nerve fibers are localized in the adventitial-medial transitional zone of the femoral artery. These findings may indicate the presence of a cholinergic vasodilatator system in the control of the circulation in the femoral artery.