The CSF changes in neurocysticercosis have been extensively studied in view of their diagnostic importance. The CSF changes in 62 human cases of neurocysticercosis are presented. In all cases the diagnosis of cysticercosis was ascertained either by surgical procedure or by autopsy. The following observations are made from the study of this material, and from the pertinent literature: 1 - More cases had their diagnosis made during life by the CSF examination alone than by any other procedure. The demonstration of specific antibodies in the CSF is the main diagnostic element. The presence of eosinophile cells is only suggestive of the diagnosis, and is complementary to the immunologic data. 2 - The occurrence eosinophile in the CSF is more pronounced in cases of higher total cell count. The presence of eosinophiles in the CSF may be secondary to other causes, and its absence does not invalidate the diagnosis of cysticercosis. The hyperergic reaction to the parasite can be evaluated through the eosinophile count, which contributes to the diagnosis in doubtful cases. 3 - Specific antibodies are present in the CSF in human cysticercosis, demonstrated by complement fixation and precipitation tests, the former being used more often. The antibodies appearing in cestoid parasitism are similar as a general rule. The immune reaction to the Cysticercus cellulosae in the CNS is greater in frequency and intensity, as compared to the other cestoids. 4 - The CSF changes are variable and do not always follow the clinical progress. The improvement in the clinical picture usually is followed by progressive disappearence of the CSF changes. The prognosis is worse with persistence of the CSF changes, particularly with a low sugar content. After surgical excision of cysticerci the CSF changes occasionally disappear, probably due to a small degree of parasitism, totally removed by surgery. Extravasation of the vesicular fluid of a cysticercus during an operation induces transient increase in the CSF changes. 5 - The CSF protein electrophoresis pattern in neurocysticercosis is similar to the pattern observed in sub-chronic or chronic inflammatory processes of the CNS and its coverings. An increase in the γ-globulin fraction is found and it is related to the intensity of the immune reaction. This globulin fraction probably contains the specific antibodies and the possibility of local production of this globulin is to be considered. The rise in γ-globulin appears early in the disease, and may precede the formation of specific antibodies. It regresses slowly when the clinical progress is good. There is a progressive increase in cases of poor evolution.