AbstractThis manuscript reports, the development and validation of a sensitive and selective assay method for simultaneous determination of α,β‐arteether and its metabolite dihydroartemisinin (DHA) in rat plasma by liquid chromatography–mass spectrometry. Chromatographic separations were achieved by gradient elution of the analytes with an initial composition of methanol–potassium acetate buffer (pH 4; 73:27, v/v) to 100% methanol in 3 min and maintained for 5 min on a Spheri‐10, RP18 (100 × 4.6 mm i.d.) column following an RP18 (30 × 4.6 mm i.d.) guard column. The total effluent from the column was split so that one‐tenth was injected into the electrospray LC/MS interface. ESI‐MS analysis was performed using a Micromass Quattro II Triple Quadrupole Mass Spectrometer equipped with an electrospray source. The MS analysis was carried out at cone voltage of 22 V with a scan range of 200–500 Da. The analytes were quantified from the [M+ K]+ ion chromatograms of α,β‐arteether at m/z 352, DHA at m/z 323, artemisinin at m/z 321 and propyl ether analogue of arteether at m/z 365. Liquid–liquid extractions with a combination of n‐hexane and hexane–ethyl acetate (8:2) were used to isolate α,β‐arteether and DHA from rat plasma. The method was validated and gave good accuracy and precision for the studied domain. Linearity in serum was observed over the range 4.375–70 ng/mL for a‐arteether and 10–160 ng/mL for β‐arteether and DHA. Percentage bias (accuracy) and within‐ and between‐assay precision were well within the acceptable range. This method was applied to study the pharmacokinetics following oral administration of α,β‐arteether (30 mg/kg) in rats. Copyright © 2003 John Wiley & Sons, Ltd.