Abstract: The colorimetric method for the determination of ephedrine and its preparations with periodic acid is reported. Ephedrine hydrochloride is oxidized with periodate at a pH about 7.2, buffered with phosphate, the acetaldehyde thus produced is separated from the reaction mixture by aeration and absorbtion in concentrated sulfuric acid, to which p-hydroxy biphenyl being added after aeration. The optical density of the bluishviolet color formed is compared with a standard graph using an electrophotometer. In the method specified, samples containing 0.005—0.05 mg ephedrine hydrochloride can be determined with an accuracy within ±5%. Factors which affect the color are studied. Lactose and glycerin give no interference. Data and details for using the method to determine ephedrine in fluid-extract and tablets are also given.