ABSTRACTThe development and validation of an LC‐MS/MS method for the simultaneous determination of albendazole metabolites (albendazole sulfoxide and albendazole sulfone) in human plasma are described. Samples of 200 μL were extracted with ether–dichloromethane–chloroform (60:30:10, v/v/v). The chromatographic separation was performed using a C18 column with methanol–formic acid 20 mmol/L (70:30) as the mobile phase. The method was linear in a range of 20–5000 ng/mL for albendazole sulfoxide and 10–1500 ng/mL for albendazole sulfone. For both analytes the method was precise (RSD < 12%) and accurate (RE <7%) with high recovery (>90%). The method was successfully applied to determine the plasma and cerebrospinal fluid levels of albendazole sulfoxide and albendazole sulfone in patients with subarachnoidal neurocysticercosis who received albendazole at 30 mg/kg per day for 7 days. This LC‐MS/MS method yielded a quick, simple and reliable protocol for determining albendazole sulfoxide and albendazole sulfone concentrations in plasma and cerebrospinal fluid samples and is applicable to therapeutic monitoring. Copyright © 2011 John Wiley & Sons, Ltd.