In 740 cases of "essential" epilepsy, cerebrospinal fluir (CSF) was studied concerning pressure, cytology, protein content, and complement fixation tests for syphilis and cysticercosis. The CSF was abnormal in 41 cases (5.5%o); in most cases the alterations were neither specific nor permanent. Among the abnormalities the mort frequent was pleocytosis and increase of protein content (29.3% each), followed by hypertension (17.0%); in 24.4% of cases with abnormal CSF an association of these abnormalities was found. The complement fixation test for çysticercosis (Weinberg test) was positive in 3 cases (0.004%). There was no significant difference of the incidence of convulsions or electroencephalographic abnormalities between all 740 cases studied and 41 cases with abnormal CSF. These findings and the ability of neurosyphilis to give rise to epileptic symptoms only (as referred in the literature) lead the authors to the conclusion that the CSF examination is indicated in all cases of epilepsy.