The reactivity of alkylperoxyl radicals and -O3SOO* toward ozone was investigated. The peroxyl radicals were produced by steady-state gamma-radiolysis in the presence Of O-3. The rate constants were extracted from the decay rate of ozone measured during the irradiation. The rate constants vary between 7 x 10(3) and 2 x 10(5) M-1 s(-1) and there is a trend of increasing rate constant with electron-withdrawing substituent. Quantum chemical computations support a mechanism, according to which formation of an alkyl trioxide radical is the rate-determining step. This is followed by rapid expulsion Of O-2 to yield the alkoxyl radical. Conceivably, the alkyl trioxide radical is preceded by an extremely unstable alkyl pentoxide radical in equilibrium with the reactants.