The temperature dependence of the rate constant for the reactions of HO2 with OH, H, Fe2+ and Cu2+ has been determined using pulse radiolysis technique. The following rate constants, k (dm(3) mol(-1) s(-1)) at 20degreesC and activation energies, E-a (kJmol(-1)) have been found. The reaction with OH was studied in the temperature range 20-296degreesC (k = 7.0 x 10(9), E-a = 7.4) and the reaction with H in the temperature range 5-149degreesC (k = 8.5 x 10(9), E-a = 17.5). The reaction with Fe2+ was studied in the temperature range 16-118degreesC (k = 7.9 x 10(5), E-a = 36.8) and the reaction with Cu2+ in the temperature range 17-211degreesC (k = 1.1 x 10(8), E-a = 14.9). (C) 2003 Elsevier Ltd. All rights reserved.