The reactions of CCl3O2. (a model of alkyl peroxyl radicals which can be selectively generated in nanoseconds) with a range of carotenoids (beta-carotene, septapreno-beta-carotene, canthaxanthin, astaxanthin, zeaxanthin, and lutein) in the heterogeneous micellar environment, aqueous 2% Triton X-100, have been studied by pulse radiolysis. For all carotenoids investigated two reaction products, absorbing in the near-infrared region, are observed and assigned to the carotenoid radical cation and an addition radical. With the exception of astaxanthin, the carotenoid radical cation formation is biexponential and the slower component matches the first-order decay of the addition radical. In the case of astaxanthin, no radical cation is formed directly by reaction with CCl3O2., it is formed exclusively from the decay of the addition radical. The results are discussed in terms of the antioxidant properties of carotenoid pigments.