The degradation rate of amitriptyline hydrochloride in buffered aqueous solution containing various additives was determined. The oxidation was a free radical-mediated process, and the rate was accelerated by the presence of metal-ion contaminants. Glass ampuls, particularly amber ones, in which the solutions were stored were the major source of these contaminants. Edetate disodium stabilized the solution, but the primary antioxidants propyl gallate and hydroquinone were less effective. Sodium metabisulfite accelerated the decomposition, and it is postulated that there was direct attack by metabisulfite at the olefinic double bond in the drug molecule.