Chronic parasympathetic decentralization of submandibular glands in rabbits has been studied after 3 weeks, in acute experiments under urethane anaesthesia. A "paralytic' secretion occurred from the supersensitive denervated glands and it was not attributable to an increase in the "spontaneous' flow, that is present in normal glands. The "paralytic' secretion was completely inhibited by atropine, after which a "spontaneous' flow, that was similar to the contralateral glands, persisted. The alpha-adrenergic blocker dihydroergotamine, when given before atropine, reduced the "paralytic' secretion by 50-75% but when this drug was given after atropine it had no additional effect. The beta-adrenergic blocker propanolol did not cause a reduction in the "paralytic' secretion. Superior cervical ganglionectomy, in contrast, did not give rise to a significant "paralytic' flow. The results suggest that acetylcholine, released spontaneously from terminals of postganglionic parasympathetic nerves, plays an essential part in the "paralytic' secretion that occurs from rabbit submandibular glands after preganglionic denervation. Circulating catecholamines make a secondary contribution, acting synergistically with the acetylcholine on the supersensitive secretory cells.