Electron paramagnetic resonance free induction decay (FID) attenuation measurements have been used to determine Arrhenius parameters for the reaction of hydrogen atoms with IO4- and IO3- in aqueous solution at pH 4.6. At 25 degrees C, scavenging rate constants of(7.31 +/- 0.12) x 10(8) and (1.22 +/- 0.04) x 10(7) dm(3) mol(-1) s(-1) were obtained for IO4- and IO3-, respectively, with corresponding activation energies, measured over the temperature range 6-75 degrees C, of 22.35 and 27.46 kJ mol(-1). From kinetic measurements in 0.10 and 1.00 M HClO4 over the same temperature range, the rate constants for hydrogen atom reaction u with the acid forms of these species, H(5)IO6 and HIO3, were calculated to be 3.5 x 10(8) and 6.0 x 10(6) dm(3) mol(-1) s(-1) (25 degrees C), with activation energies of 53.00 and 36.55 kJ mol(-1), respectively. We suggest that all of these reactions involve oxygen atom transfer to the hydrogen atom, giving .OH and a reduced iodine complex as product.