The fate of long-lived species [pyrene (Py) radical cations and Py-cyclohexadienyl-type radicals] generated by electron-beam irradiation at room temperature in poly(methyl methacrylate) (PMMA) doped with Py is described. The separation of reacting solute intermediates and the relaxation phenomena seem to be the main factors limiting the reactivity of long-lived Py species in the PMMA matrix. The temperature-stimulated recombination of ionic species in PMMA doped with Py results in Py excited-state formation.