Abstract: After a brief review of the methods for the conversion of organic iodine, the author suggests a method for the determination of iodine in acetrizoic acid — a new and excellent contrast medium for excretory urography, by alkaline reduction with zinc powder, following the argentimetric determination in which the starch iodide method of Kolthoff is used. The experimental conditions of this method regarding the duration ot boiling time, quantity of zinc, concentration of sodium hydroxide solution, method of iodide estimation, precision, accuracy, etc. are systematically investigated. From the results shown, 0.0002-0.0003 M sample in 40 ml 0.6 N sodium hydroxide solution, added by 1 gm zinc and boiled for 10 minutes, suffices to meet quantitative requirements. The accuracy is 0.25% or better. A precision study of this method, in which 12 replicate analyses were made, gave a maximum deviation of±0.19%. A single determination can he made in 30 minutes at one time, and for routine work 4 samples per hour can be run. It is concluded that this method, in respect of its simplicity, rapidity, and reproducibility, can be employed to supersede the official method specified in the Pharmacoposia of the United States of America (XV Ed.) which is rather tedious and time-consuming in operation. The proposed procedure is summarized as follows: To about 0.15 gm sample accurately weighed (with injection solution, a volume containing 0.15 gm of the labelled amount is pipetted.) in a 150 ml flask, add 30 ml sodium hydroxide test solution with gently shaking to dissolve the powder. Add 1 gm zinc powder and 10 ml distilled water to wash down any adhesion of the sample on the wall of the flask, attach a condenser and boil over a direct flame (separated from the flask by an asbestos board) for 10 minutes. Cool, rinse the condenser twice, each time with 20 ml water, filter and wash the residue 3 times each with 15 ml water. Combine the washings with the filtrate prior to acidification with dilute nitric acid (1:10) to litmus red. Add 2 ml starch indicator and 2-4 drops of potassium permanganate test solution, and then titrate with 0.05 N silver nitrate until the blue colour is just discharged, leaving a canary yellow precipitate. Each ml of 0.05 N silver nitrate is equivalent to 6.346 mg iodine or 9.648 mg C₉H₅I₃NNaO₃.