The adrenergic innervation of structures in the gills of six teleost species was studied with catecholamine fluorescence histochemistry. The species studied were the following: sand flathead, Platycephalus bassensis and blue-spot flathead Platycephalus caeuruleopunctatus (Platycephalidae); smooth toadfish, Tetractenos glaber (Tetraodontidae); Australian short-finned eel, Anguilla australis (Anguillidae); river blackfish, Gadopsis marmoratus (Gadopsidae); and common carp Cyprinus carpio (Cyprinidae). In all species except C. carpio fluorescent components were observed in the branchial nerves in the gill arch. In the arterio-arterial vascular pathway, the afferent and efferent branchial arteries were innervated only in Cyprinus. Fluorescent nerve fibres were found on afferent filamental arteries of all species except A. australis and on many afferent lamellar arterioles of all species except T. glaber. The secondary lamellae were devoid of fluorescent nerve fibres in all species. In Cyprinus and Anguilla, fluorescent nerve fibres were observed on occasional efferent lamellar arterioles. In Cyprinus, there was an additional innervation on the basal one-third of the efferent filamental artery. The innervation of the arteriovenous vascular pathway was similar in all species. Fluorescent nerve fibres were found on nutritive arterioles, and in the core of each filament between the surface epithelium and the wall of the filament venous sinus. Since most of the adrenergic innervation was found on afferent vessels of the arterio-arterial pathway, it is suggested that adrenergic nerves and circulating catecholamines may have distinct functions in the regulation of blood flow through the gills.