To determine the plasmatic and intracystal concentrations of albendazole sulfoxide (AS) and correlate them with the viability of the scolices in patients surgically treated for hepatic hydatid cysts (HHC) that received albendazole preoperatively, as an indirect way of evaluating the scolicide efficacy of the drug. A non-consecutive series of patients with uncomplicated HHC, underwent operation at the Department of Surgery, Regional Hospital of Temuco, Chile, between 2001 and 2002. The patients were given 10 mg/kg/day of albendazole for 4 days prior to the surgery. Intraoperative samples of venous blood and hydatid fluid were taken, in which the plasmatic concentration (PIC) and intracystal concentration (ICC) of AS were measured by means of high-performance liquid chromatography. With the remaining hydatid fluid, the viability of the scolices was examined. The following variables were taken into consideration: diameter, type of cyst, number of cysts, and development of cyst-biliary communications. Descriptive statistics were used in the calculation of medians, averages, and standard deviations, and analytical statistics were used for the comparison of continuous variables applying the t-test and the Mann-Whitney U-test. A total of 26 patients with HHC, with a median age of 39.5 years (range: 16-80 years); 16 were women (61.5%). Nineteen patients presented only one cyst (73.1%), and the diametric median of the cysts was 14.5 cm (range: 7-30). Fourteen patients presented univesicular cysts (53.9%), and the remaining 12 had multivesicular cysts (46.1%). The average PIC of AS in the whole series was 1.88 +/- 0.5 microg/ml and the ICC was 0.26 +/- 0.2 microg/ml. The ICC in viable hydatid cysts was 0.25 microg/ml versus 0.28 microg/ml in non-viable cysts (p = 0.7556). The absence of association between intracystal levels of AS and the viability of the scolices allows one to posit indirectly that albendazole is ineffective as a scolicidal agent administered preoperatively for 4 days.