By means of fluorescent-histochemical method distribution of monoaminergic structures has been studied in the sympatho-adrenal system of the carp (Cyprinus carpio L.) mesonephros. Catecholaminergic nervous fibers are revealed in the walls of adrenal and venous vessels and glomerular arterioles. In the glomerular capillaries they are not found. In the walls of the venous vessels, besides catecholamine-containing nervous fibers, chromaffin cells with long processes running along the vessel are observed. Some contacts of catecholamine-containing structures of the mesonephric vascular wall with the proximal and, very seldom, with distal parts of the nephron canaliculi are demonstrated. Structures containing indolamines are not revealed.