Electroencephalographic (EEG) electrodes and ventricular cannulae were implanted in 8 rabbits and 12 rats. Two anti-cholinergic agents, atropine sulfate and scopolamine hydrobromide, were given systemically (1-50 mg/kg) and intraventricularly (5-800 mug). Systemic but not intraventricular injections blocked sensory stimulation-induced or eserine-induced neocortical desynchronization and hippocampal RSA in rats and rabbits which were immobile and either undrugged or ethanol intoxicated. Systemic injections also blocked hippocampal RSA but not neocortical desynchronization in rats given sensory stimulation under urethane anaesthesia, while intraventricular injections only reduced RSA amplitude. Neither systemic nor intraventricular injections blocked neocortical desynchronization or hippocampal RSA recorded from animals when they walked in a motor driven wheel. These experiments support the hypothesis that there are two types of neocortical desynchronization and hippocampal RSA, one cholinergic and one non-cholinergic. They also suggest that atropine and scopolamine pass more readily to the neural system responsible for cholinergic EEG activity from the capillary bed than from the ventricular fluid.