Dual spin polarization of CIDEP signal of radicals produced in benzil/triethylamine in the benzene system was investigated by the time-resolved ESR and transient absorption technique. CIDEP signals showed absorption or emission depending on the concentration of triethylamine. Emissive CIDEP signal was observed below 10(-3) RI of triethylamine, whereas absorptive signal was observed above 10(-1) M. The dual CIDEP signal was explained by the triplet mechanism (TM) and the radical-triplet pair mechanism (RTPM); the absorptive polarized TM signal was generated from the reaction- of free triplet benzil with triethylamine, whereas the emissive polarized CIDEP signal was generated through the interaction between tripler benzil and benzil ketyl radical produced from the benzil-triethylamine complex.