Auditory cortical cvokod rcsponse(ACER) and auditory brainstom cvoked response(ABR) were recorded in guinea pigs before and after irradiation of ~(60)Co γ-ray. A single dose ofirradiation on head was 90Gy and 70Gy in two groups, respectively. Two h after irradiation. thethreshold shift was 12. 5 dB and 9 dB, and the ACER (?) post-irradiation amplitude ex-ceeded the maximum pre-irradiation value by 20% and 37%. Six h after irradiation, the thresholdshift increased to 37 dB and the maximum amplitnde decreased to the level of pre-irradiation in70Gy-group. In another group, right auditory bulla arca was irradiated with a total dose of 45Gy ina course of six fractions/two weeks. Fourteen d after irradiation, the threshold shift of ABR was 118dB and the latency of wave I was longer. The amplitude-intensity curve was (?) afterirradiation. Histological observation using scanning (?) showed that only outer hair-cells in the basal coil of the cochlea were (?) 6 h after irrdiation 50Gy-group. Bul 16 hlater, outer, hair cells in all coils of the cochlea were found to be destroyed extensively and inner (?)cells were destroyed slightly. In 45Gy-group, 14 d after irradiation, outer hair cells in all coils of thecochlea were damaged and no inmer hair cell was injured severely. Auditory cortical cvokod rcsponse (ACER) and auditory brainstom cvoked response (ABR) were recorded in guinea pigs before and after irradiation of ~ (60) Co γ-ray. A single dose ofirradiation on head was 90Gy and 70Gy in two groups, respectively. Two h after irradiation. The threshold shift was 12. 5 dB and 9 dB, and the ACER (?) Post-irradiation amplitude ex-ceeded the maximum pre-irradiation value by 20% and 37%. Six h after irradiation, the threshold shift increased to 37 dB and the maximum amplitnde decreased to the level of pre-irradiation in 70 Gy-group. In another group, right auditory bulla arca was irradiated with a total dose of 45 Gy ina course of six fractions / two weeks. Fourteen d after irradiation, the The amplitude-intensity curve was (?) afterirradiation. Histological observation using scanning (?) showed that only outer hair-cells in the basal coil of the cochlea were (? ) 6 h after irrdiation 50Gy-group. Bu In 45 Gy-group, 14 days after irradiation, outer hair cells in all coils of the cochlea were damaged and no inmer hair cell was injured severely.