Simple, rapid, reliable and fully validated voltammetric methods were developed for the determination of zafirlukast in pharmaceutical formulations, based on its electrochemical reduction at a hanging mercury drop electrode. Its electrochemical behavior in borate buffer (pH 8.0) was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The linear sweep voltammetric study of zafirlukast was carried out using glassy carbon eletrode. A well-defined cathodic peak at -1326 mV without the adsorptive accumulation time and at -1312 mV with 20 s of accumulation time versus Ag/AgCI reference electrode in square-wave and square-wave adsorptive stripping voltammetric methods, respectively, was observed. The experimental and instrumental parameters affecting the peak cur-rent of zafirlukast were investigated and optimized for the zatirlukast determination. The detection limits of square-wave and square-wave adsorptive stripping voltammetric methods were 50 and 5 ng mL(-1) with R.S.D. of 6.79 and 5.72%, respectively. The methods showed good sensitivity, accuracy, precision, selectivity, robustness and ruggedness. The proposed methods were applied for the determination of zafirlukast in its pharmaceutical formulations. The results obtained from developed methods were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically. (c) 2005 Elsevier B.V. All rights reserved.