The kinetics and mechanism of the oxidation of I- to I-2(center dot-) by (OH)-O-center dot and O center dot- in alkaline aqueous solution have been re-investigated by pulse radiolysis combined with optical detection. The data are shown to be consistent with k((OH)-O-center dot + I- HOI center dot-) = 1.6 x 10(10) and k[O center dot- + I- (+H2O) -> HOI center dot- + OH-] = 2.0 x 10(9) dm(3) mol(-1) s(-1), respectively, and the reversible dissociation of the adduct HOI center dot- into I-center dot and OH- with k(f)[HOI center dot-) = 3.5 x 10(7) s(-1) and k(r)(I-center dot + OH-) = 1.6 x 10(8) dm(3) mol(-1) s(-1) so that pK(a)(I-center dot (.) H2O) = 13.3. There is no evidence for the reactions HOI center dot- -> (OH)-O-center dot + I- and HOI center dot-+ I-2(center dot-) -> I-3(-) + OH-. The equilibrium HOI center dot- + I- reversible arrow I-2(center dot-) + OH- reported in the literature [H. Buchler, R.E. Buhler, Chem. Phys. 16 (1976) 9-18; H. Shiraishi, H. Okuda, Y. Morinaga, K. Ishigure, JAERI - M 92-012, 152-161.] in 10 mol dm(-3) hydroxide solution is not detectable at pH 13. (c) 2006 Elsevier B.V. All rights reserved.