A nonaqueous capillary electrophoretic method (NACE) for the fast determination of plasma levels of albendazole (ABZ), albendazole sulfoxide (ABZSO), and albendazole sulfone (ABZSO(2)) is described. TI-le assay is based upon liquid/liquid extraction of these compounds using dichloromethane at pH 10.2 (recovery between 63 and 98%), followed by a NACE separation performed within 8 min employing a 0.036 M berate buffer (apparent pH 9.9) in a mixture of methanol and N-methylfermamide (1:3) and on-column absorbance detection at 280 nm. Using 0.5 mt of plasma and extract reconstitution in 200 mu L N-methylformamide, drug levels between 1.0-10 mu M were found to provide linear calibration graphs. Intraday and interday imprecisions evaluated from peak area ratios (n = 5) were < 10% and < 12%, respectively. Corresponding imprecisions of detection times (n = 5) were < 1% and < 6%, respectively. The limit of detection (LOD) for ABZ, ABZSO and ABZSO(2) was 8 x 10(-7) M. The reliability of the method developed was verified via analysis of 45 plasma samples obtained from patients treated with ABZ. Good agreement was obtained between the levels of ABZSO and those determined by routine HPLC. ABZ was found to be undetectable in all patient samples, whereas the levels of ABZSO(2) were below or close to LOD.