The cardiac ganglia in Japanese quail were studied with the use of histological, histochemical and ultrastructural techniques. Histological investigations revealed the presence of a number of cholinergic ganglia in the fatty tissue of the epicardium. They were grouped in plexo-ganglionic forms localised in three regions: 1) on the ventral surface of the cardiac atria, 2) on the ventral surface of the cardiac ventricle, 3) on the dorsal surface of the cardiac ventricle. These plexoganglia are structures composed of many ganglia differing in size (from 77 microns to 577 microns length and from 53 microns to 163 microns width), connected by fascicles of nerve fibres. The cells of cardiac ganglia have single, round or oval nuclei with one or several dense nucleoli. There were myelinated and unmyelinated fibres in the intercellular spaces. Rough endoplasmic reticulum (RER) and free ribosomes were localised mainly in the perinuclear part of the cytoplasm. In the peripheral part, RER was less abundant, but mitochondria were more numerous in this part of the cytoplasm. In the peripheral parts of the neurones, axo-somatic synapses were usually observed. Profiles of the end sections of axons contained two kinds of synaptic vesicles: small, agranular ones and among them large ones with a dense core.