We investigated the effects of the antioxidant edaravone against acoustic trauma in guinea pigs. Edaravone (1.722 x 10(-2) M) was infused into the right ear by an osmotic pump, and the left ear was untreated for control. Animals received edaravone 9 h before (-9 h group, n = 7) and 9 h (+9 h group, n = 8), 21 h (+21 h group, n = 7) and 33 h (+33 h group, n = 4) after 3-h exposure to 130-dB noise. Seven days after noise exposure, we examined the shift in auditory brainstem response thresholds and histopathologic characteristics of the sensory epithelia. The smallest shift in auditory brainstem response threshold and smallest proportion of missing outer hair cells were observed in the +9 h group. This result was supported by immunohistochemical analysis of 4-hydroxy-2-nonenal. Our data suggest that edaravone may be clinically effective in the treatment of acoustic trauma, especially if given within 21 h of noise exposure.