The cerebrospinal fluid changes of 115 cases of cysticercosis of the central nervous system are studied. The diagnosis was based upon the demonstration of specific antibodies in the CSF by a complement fixation test for cysticercosis. The following observations are made: 1 - the CSF changes in CNS cysticercosis may be grouped as one of the CSF syndromes; 2 - the main alteration is the presence of specific antibodies for cysti-cerci, demonstrated by a complement fixation test; the positivity of this reaction is the most reliable element in the biologic diagnosis of this disease; 3 - eosinophile cells are commonly found in the CSF in cysticercosis, and their presence is an accessory element to the complement fixation test in problem cases; 4 - pleocytosis, slight increase in the total protein content and parenchymatous deviation in colloidal reactions are usually found in cysticercosis. Increase of the CSF pressure and a reduction of the glucose contents are occasionally found; 5 - the examination of these data as a whole yield informations regarding to the diagnosis, prognosis and clinical progress in cases of cysticercosis of the CNS.