Cyclic adenosine-3’,5’-monophosphate (cAMP) concentration in cerebrospinal fluid (CSF) was measured by the protein binding method of Gilman from 62 neurological patients, 46 of them were epileptics and 16 with a central nervous system (CNS) damage. In epileptic patients the CSF concentration of cAMP was significantly elevated (p<0.02) for 3 days after an attack when compared with those free from attacks for at least 2 weeks. The causality relationship between the rise of cAMP in CSF and an epileptic discharge is discussed. In patients with an active or rapidly progressing CNS damage the cAMP levels in the CSF were significantly higher (p<0.001) than in those with an old CNS damage. Also some enzyme activities in CSF were measured but no uniform alterations could be found. In damaging processes of the CNS, the cAMP values in the CSF seem to correlate to the activity of the dise