A comparison of three different methods (HPTLC-densitometry, HPLC, CE) developed for the photostability testing of isoxicam is presented. The stability indicating capability of the assays is proved using forced degradation by exposing a sample solution to artificial irradiation from a xenon source. The chromatograms and electropherogram of the resulting solution show isoxicam well resolved from the degradation products. For quantitation, external calibration is employed, all calibration curves being linear in the respective concentration range of interest. Photodegradation of isoxicam is studied with special emphasis on the investigation of the correlation between concentration of the sample solution and the stability. Isoxicam solutions of three different concentrations (2 mg ml - 1 ; 250 μg ml - 1 ; 40 μg ml - 1 ) are subjected to simulated sunlight for 480 min and tested for stability. The methods are compared in respect of performance, precision, detection and quantitation limits.