A photocolorimetric method was developed for determining anesthesin in ointments and tablets, and the feasibility of using it to establish the stability of preparations containing anesthesin was studied. The method is accurate and reproducible, with a relative error of .ltoreq. .+-.3.0%. Maximum absorption of reaction products occurs at 520 nm. The smallest quantity of anesthesin which can be determined is 0.02 mg/ml.