Hair cell damage in chick cochlea following chronic treatment of kanamycin was examined at light or electron microscopic level. Four day-old chicks were given intramuscular injection of kanamycin at a dose of 200mg/kg for 10 days and sacrificed 3 days after the last injection. Obvious damage of hair cells was identified in the middle to distal region on the basilar papilla, especially at its inferior side, while hair cells in the proximal region were morphologically intact. These results support our behavioral data suggesting low frequency selective effects of kanamycin in the avian inner ear.