This study was designed to investigate the ototoxic side effects of furosemide in inner ears of 20 Lewis rats. 16 rats were divided into two groups experimentally : One was single intraperitoneal injection of furosemide(100 mg/kg) and the other was repeat injection two days later. 8 rats were used in each group and 4 were as control. Changes of inner ear were examined at 1 hour and 5 hours after injection by means of Auditory Brainstem Response(ABR), light microscopy and electron microscopy. On ABR study, in single injection group, wave I latency was markedly delayed at 1 hour and slightly delayed at 5 hours. In repeat injection group, wave I latency was not shown at 1 hour but markedly delayed at 5 hours. On light microscopic findings, the cells of the stria vascularis were slightly edematous in single injection group and more prominent in repeat injection group, but Reissner membrane was not changed. On electron microscopic findings, widening of intercellular spaces between marginal cells, swelling of the intermediate cell with vacuolar change and increase of lysosome were characteristics in both groups at 1 hour but more prominent in repeat injection group. These findings were seemed to be recovered at 5 hours. From the above results, it would be suggested that ABR and morphological changes were related to each other and functional disturbance of inner ear might be induced by alternation of hemodynamics of endolymph and influencing to neuroepithelial cells.