The rate constant for the reaction of the hydroxyl radical with iodine was estimated to be (9.5 ± 1.0) × 109 dm3 mol−1 s−1 at 20 °C from fitting the time dependence of the decrease in the absorption of iodine at 460 nm. A number of rate constants associated with the decay of I2− that were required for this fitting process were also determined. They were the reaction of I2− with I2− (2k = (4.6 ± 1.6) × 109 dm3 mol−1 s−1) at an ionic strength of 1.2 × 10−2 mol dm−3; I2− with I (k = (4.6 ± 1.6) × 109 dm3 mol−1 s−1); and I with I (2k = (3.0 ± 1.0) × 1010 dm3 mol−1 s−1).