The autonomic outflow and sensory structures in the ovary and accessory reproductive organs of the hamster are described by means of specific fluorescence and enzyme histochemical techniques for the demonstration of catecholamine and acetylcholinesterase (AChE), respectively. Sympathetic nerves accompany branches of the major blood vessels in the mesentery of the ovary, oviduct and tubal uterine horn and invest the vascular bed in each of these organs. Vasomotor fibers predominate in the ovary and oviduct, though occasional adrenergic axons supply thecal and interstitial tissues in the ovary and the longitudinal smooth muscle of the oviduct. Fluorescent myomotor axons run in the suspensory ligament and outer myometrial layer of the uterus, but most of the numerous sympathetic and AChE-fibers in the tubal third of the horn supply the intramural and submucosal vascular plexuses. A limited electron microscopic study of the central spiral (preplacental) arteries of the endometrium indicates that the surrounding terminal AChE-fibers are identical to the fluorescent and granular vesicle-bearing adrenergic axons which form neuromuscular junctions with these vessels. Based on the discovery of specialized sensory endings in the walls of the large collecting veins which drain the hamster uterus, a mechanism is proposed to account for the regulation of blood flow through maternal placental vessels which are devoid of an arteriolar neuromuscular apparatus.