A stability-indicating assay method based on reverse-phase high-performance liquid chromatography has been developed for the quantitation of triamcinolone acetonide. The method was used to study the stability of triamcinolone acetonide in water--ethanol solutions of varying pH, buffer concentration, and ionic strength. The decomposition of triamcinolone followed pseudo-first-order law and was minimal at pH approximately 3.4. Above pH 5.5, the decomposition increased rapidly and was directly related to phosphate buffer concentration. The decomposition decreased with increasing ionic strength when the pH of the solution was greater than 7. Two new peaks corresponding to decomposition products were noted in the chromatogram; their ratio varied significantly with the composition of the vehicle.