Zafirlukast is a selective and competitive orally administered inhibitor of the cysteinyl leukotrienes and currently indicated for the prophylaxis and treatment chronic asthma. A simple, rapid, reliable capillary zone electrophoresis method for the determination of ZAF in pharmaceutical formulations was developed and validated. The influence of buffer concentration, buffer pH, organic modifier, capillary temperature, applied voltage and injection time was systemically investigated in a fused silica capillary (i.d. 50 mu m, total length 80.5 cm and effective length 72.0cm). Optimum results were obtained with 50 mM borate buffer at pH 8.50, capillary temperature 25 degrees C and applied voltage 30 kV. The samples were injected hydrodynamically for 3 s at 50 mbar. Detection wavelength was set at 240 nm. Meloxicam was used as internal standard. The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, selectivity, robustness and ruggedness. The linear calibration range was 2.00-80.00 mu g mL(-1) and the limits of detection and quantification were 0.75 and 2.00 mu g mL(-1) with R.S.D. of 3.88 and 2.75%, respectively. The proposed method was applied for the determination of ZAF in its pharmaceutical formulations. The results obtained from developed method were compared with a HPLC method reported in the literature and no significant difference was found statistically. (c) 2007 Elsevier B.V. All rights reserved.