The chemical behavior of the triplet molecules of exo- and endo-5-vinyl-2-norbornene, radiation- and photochemically generated in benzene and cyclohexane, were studied in the presence of the triplet sensitizer acetophenone. It was found that the endo-isomer was rearranged to [4.2.1.0(2,5).0(3,7)]nonane, and the exo- isomer remained unchanged. In the absence of acetophenone, the rearrangement of the endo-isomer did not occur. It was concluded that in the initial stages of the gamma radiolysis of diene solutions in benzene and cyclo-hexane, the triplet excitation did not transfer from the solvent molecules to the diene molecules. In benzene, diene is consumed in the reaction with neutral radicals, the products of the decomposition of the solvent triplet molecules. In cyclohexane, diene molecules are activated as a result of the transfer of the positive charge from the solvent molecule.