A method is presented for the quantitative determination of tetracaine and phenylephrine hydrochloride in therapeutic preparations based on ultraviolet spectrophotometry and colorimetry. Tetracaine absorbs light strongly in the spectral region of 310 mμ, while phenylephrine shows negligible absorption at this wave length. Phenylephrine is determined colorimetrically by a modification of a nitrosation method for phenols. Tetracaine is separated from its hydrolytic product, p-butylaminobenzoic acid, by extraction with water-saturated benzene below pH 3 and the concentration of tetracaine estimated in the aqueous solution, adjusted to a pH between 6 and 8, by measuring its optical density at 310 mμ. Phenylephrine solutions are treated with 15 per cent mercuric sulfate in 5 N sulfuric acid, heated on a water bath, cooled to room temperature, diazotized with 0.1 per cent sodium nitrite and diluted with distilled water. The red color developed is estimated in a colorimeter at 495 mμ and the concentration of phenylephrine determined by reference to a suitable standard.