A study was made of the intrathecal infusion as a route of administration of drugs for the CNS, by giving due consideration to the presence of blood-brain and CSF-brain barriers. CDP-choline was used as the brain activator, and the effect of the drug intrathecally infused was investigated both clinically and by experiments on animals. Seven patients with a disturbance of consciousness due to primary brain lesion received a total of 19 intrathecal infusions of CDP-choline, and were examined for the effect of the treatment neurologically and electroencephalographically. Wistar rats were infused either intravascularly or intracisternally with 14C-CDP-choline, and the distribution in the body was investigated by whole body autoradiography.