Free radicals and antioxidants may play a role in the etiology and pathogenesis of some central nervous diseases. The brain tissue is relatively insufficiently protected by antioxidants against the free radical induced damage. The brain situation may be reflected by the cerebrospinal fluid examination, which has not enough attention. It seems, that from this point of view subarachnoical hemorrhagy, meningitis, hydrocephalus, Alzheimer's, Parkinson's and Huntington's diseases, multiple sclerosis and probably schizophrenia should receive a special attention.