The effectiveness of praziquantel on the infestation of the central nervous system by Cysticercus cellulosae is evaluated considering observations of 20 patients followed from July, 1979 and October, 1980. Two series of 6 day oral administration of the drug were scheduled for each patient: 20 mg/kg/day were given to the first 10 patients in the two series and 30 mg/kg/day to the second 10 patients in the two series. Transient exhacerbation of the cerebrospinal fluid changes proper to neurocysticercosis coincidental the series of medication was the mainline to consider the results. Cytologic aspects of this response was previously reported, and the remarkable participation of eosinophil cells was pointed out. It occurred in 15 patients. Corticosteroids interfere both is the intensity and in the type of this response. Data support the action of praziquantel on cysticerci which parasites the central nervous system and suggest the use of larger doses of the drug and/or a larger period of administration to obtain more effective results.