A rapid, sensitive and specific method for quantifying the aromatase inhibitor (anastrozole) in human plasma using dexchlorpheniramine as the internal standard (I.S.) is described herein. The analyte and the I.S. were extracted from 200 mu l of human plasma by liquid-liquid extraction using a mixture of diethyl ether: dichloromethane (70:30, v/v) solution. Extracts were removed and dried in the organic phase then reconstituted with 200 mu l of acetonitrile: water (50:50; v/v). The extracts were analyzed by high performance liquid chromatography coupled with photospray tandem mass spectrometry (HPLC-MS-MS). Chromatography was performed isocratically on a Genesis, C18 4 mu m analytical column (100 mm x 2.1 mm i.d.). The method had a chromatographic run time of 2.5 min and a linear calibration curve ranging from 0.05-10 ng ml(-1). The limit of quantification (LOQ) was 0.05 ng ml(-1). This HPLC-MS-MS procedure was used to assess pharmacokinetic studies. (c) 2006 Elsevier B.V. All rights reserved.85041671553559