ACh synthesis and content in the cerebral cortex and brain stem as well as the activity of choline acetylase (AcCh) and acetylcholinesterase (AchE) in brain homogenates were determined after NA administration both in vivo and in in vitro. In in vivo experiments NA was injected intraperitoneally or into the lateral ventricle of the brain. Intraperitoneal injection of NA caused a significant fall of ACh content in the cerebral cortex. AchE activity was inhibited after intraventricular NA injection and in in vitro investigations, in which NA was added into the incubation medium. ACh synthesis and AcCh activity showed no abnormalities after NA administration in vivo and in vitro.