A method for the determination of iodine is described, based on the reaction of acetone, iodine and potassium hydroxide as monitored with an iodide-selective electrode. This method is more sensitive than those previously de~cribed.l-~ Kinetic methods of analysis and ion-selective electrodes have recently been recognised as useful means for the determination of individual elements, catalysts, enzymes, substrates, inhibitors and activator^.^-^ In a previous paper Altinata and Pekin described the determination of molybdenum and tungsten by using an iodide-activity electrode.10Nikitin and Kochkin4 have determined iodine by using a kinetic method, based on the determination of the rate of development of turbidity in solution with time. Three readings were taken of the turbidity time (tz) and they carried out similar measurements on two control solutions (tl and t2). They calculated the concentration of the iodine used as a substrate for the reaction between acetone, iodine and potassium hydroxide by applying the equation given in the literature.There are three steps in the reaction between acetone, iodine and potassium hydroxide. These partial reactions can be summarised as the following net reaction: