Falck-Hillarp fluorescent histochemistry, analyses of catecholamine content in different organs and experiments with drug effects on isolated strip preparations were used to study the adrenergic system of the Florida spotted gar, Lepisosteus platyrhincus. The study reveals a well developed system of adrenergic nerve terminals, especially in blood vessels and in the wall of the sinus venosus and atrium. The lung (swimbladder) receives an excitatory cholinergic nerve supply which controls both smooth and striated muscle in the trabeculae of the lung. No conclusive evidence for an adrenergic inhibitory innervation of the lung was obtained. Chromaffin cells line the walls of the posterior cardinal veins, similar to the situation in the teleosts, and the dominating catecholamine in the chromaffin tissue and in the blood plasma is adrenaline. The concentration of adrenaline in the blood plasma is high enough to affect the contraction force of the heart, and circulating adrenaline may thus contribute to the adrenergic control of the heart in this species.