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A sensitive, simple and specific high performance liquid chromatography-electro spray ionization mass spectrometry method was developed for the determination of ilaprazole in the plasma of beagles administered via i.v. bolus doses of ilaprazole. The procedure employed buspirone as the internal standard and a simple protein precipitation step. The separation was achieved using a C18 column (100 mm x 2.1 mm, 5 microm) with a mobile phase consisting of water-methanol-acetonitrile (69:8:23, v/v/v) containing 0.1% (v/v) formic acid at a flow rate of 0.2 mL/min. The detection was accomplished by a mass spectrometer using selected ion monitoring (SIM) in positive mode. The linearity was from 5 microg/L to 10,000 microg/L with a sensitivity of 5 microg/L as the lower limit of quantification. The inter- and intra- day precisions were within 9.00%. The mean recoveries at three spiked levels were about 106% and the matrix effects were less than 142.0%. The method described above was successfully applied to analyze the beagle plasma samples of ilaprazole in a pharmacokinetic study. The area under the plasma concentration-time curve (AUC(0-infinity) of ilaprazole after i.v. doses of 0.2, 0.8 and 3.2 mg/kg were (2.4 x 10(4) +/- 3 x 10(3)), (8.8 x 10(4) +/- 1.6 x 10(4)) and (5.4 x 10(5) +/- 8 x 10(4)) microg/L x min, respectively. On the basis of AUC, the pharmacokinetic property of ilaprazole was proposed to be linear dynamics.