Chinchillas were exposed to a noise band (1,414 to 5,656 Hz, 100-dB sound pressure level [SPL] for one hour) and treated with kanamycin (150 mg/kg a day until hearings loss was noted at 6.0 kHz) either separately, simultaneously, or sequentially. Simultaneous noise and kanamycin resulted in interactive potentiation of threshold shift and cochlear pathologic condition. Kanamycin treatment two months after noise exposure produced similar potentiation. No interaction was seen when noise exposure occurred one month after kanamycin treatment.