Abstract: Ten ml of a solution of emetine hydrochloride in 1:1 diluted hydrochloric acid (containing up to 0.1 mg of anhydrous salt per ml), warmed to 40℃, was treated with 0.20ml sodium hypochlorite solution (containing about 2.6—2.8 mg Cl₂ per 100 ml), and the orange-yellow colour developed was measured within 10—25 minutes interval in a colorimeter using a 460 mμ filter. The colour intensity was found to obey Beer's law. The method was found to give results in close agreement with the official method adopted in Chinese Pharmacopoeia 1953.