The innervations of the gizzards of the chick and pigeon have been examined using histochemical methods for the localisation of catecholamines and cholinesterases. The perivascular sympathetic nerve trunks of both species contain cholinergic and noradrenergic fibres. The vagal nerve trunks contain mostly cholinergic nerve fibres, although a few noradrenergic fibres are present below the level of the vago-aympathetic anastomoses. The arterial vasculatures of the gizzards of both birds appear to receive a dual noradrenergic-cholinergic innervation. The main body of Auerbach's plexus is composed of noradrenergic nerve fibres and cholinergic ganglion cells, together with ganglion cells containing an unidentified transmitter. Very rarely, there appear to be catecholamine-containing ganglion cells present in Auerbach's plexus of the chick gizzard. In both birds the extensions of Auerbach's plexus into the musculature are composed of cholinergic ganglion cells that have noradrenergic and cholinergic nerve fibres associated with them. The smooth muscle of the gizzard receives an extensive cholinergic innervation, whereas the noradrenergic nerve fibres running in the muscle appear to be associated only with ganglion cells or blood vessels.