Albendazole or praziquantel were measured in plasma and cerebrospinal fluid (CSF) in 29 patients with neurocysticercosis. Mean levels of albendazole in plasma were 0.918 microgram/ml and in CSF were 0.392 microgram/ml and levels of praziquantel were 1.640 micrograms/ml in plasma and 0.398 microgram/ml in CSF, after doses of 15 and 50 mg/kg, respectively. Drug concentrations in CSF were 43% for albendazole and 24% for praziquantel. The drug levels obtained for both drugs showed ample individual variations that were not related to age, sex, presence of inflammation in the subarachnoid space, or therapeutic effectiveness; such variations seem to be due to individual differences in pharmacokinetics. Both drugs were effective and the doses currently used of each drug seem to be optimal for therapy of neurocysticercosis.