The optical absorption spectra and the epr signals of irradiated anthracene crystals have been measured at 4.2 and 77 K. The optical absorption and the simple Hückel calculations combined with isochronal annealing of the crystals have revealed that 9-, 1-and 2-dibenzocyclohexadienyl radicals are unstable at temperatures higher than 420, 250 and 220 K, respectively. The epr analysis has supported the result of the optical analyses of 9-, 1-and 2-dibenzocyclohexadienyl radicals, and their hyperfine coupling constants are in good agreement with the values calculated. The epr analysis connected with the isochronal annealing has revealed that three phenyl-type radicals are produced in the crystals at low temperature. They have been assigned as 9-, 1-and 2-anthracyl radicals with the line shapes of singlet, doublet and triplet, respectively. Their hyperfine splitting constants are almost in accordance with those obtained in an argon matrix system, and they are unstable at temperatures higher than 130, 200 and 240 K in the order of 9-, 1-and 2-anthracyl radicals. The decay processes of the cyclohexadienyl-and phenyl-type radicals have been discussed in connection with chemical reactions in the crystals. The migration of the radical species in the course of the reactions has been qualitatively confirmed by the microwave power saturation curves of the epr spectra.