Reactivity of the peroxynitrite ion toward a number of inorganic radicals was determined by using the pulse radiolysis technique. The rate constants for the oxidation of the ONOO-ion by CO3.-, N-.(3), and ClO2. radicals were determined from their decay kinetics to be (7.7 +/- 1.2) x 10(6) (I = 0.6 M), (7.2 +/- 0.9) x 10(8), and (3.2 +/- 0.3) x 10(4) M-1 s(-1), respectively. For the (OH)-O-. radical, the rate constant of (4.8 +/- 0.8) x 10(9) M-1 s(-1) was obtained by using competition kinetic analysis. The oxidation potential of the ONOO- ion was estimated as 0.8 V from the kinetic data. Although thermodynamically favorable, oxidation of ONOO- by the (NO2)-N-. radical was not observed; an upper limit of 2.5 x 10(4 )M(-1) s(-1) could be set for this reaction. Contribution from some of these reactions to the decomposition of peroxynitrite in the presence and absence of CO2 is discussed.