There are several methods about the treatment of noise induced hearing impairment in connection with its pathogenesis. One of them is based on the theory that the hearing damages were induced by means of local vasoconstriction. So they recommended the vasodilators as a treatment. Nakamura (1964) obtained good result with niacin to patient suffering from noise induced hearing damage. The other is that hearing damages were induced by means of decrement of energy in cochlea. Therefore, A.T.P. was first used by Faltyneck and Vesely (1964) to patient sufferring from noise induced hearing damage. Vitamins, sedatives, promoting agents of metabolism and vasodilators were recommended as anothod of treatment reliable evidences of effects of above various treatment were not proved yet. As a experiment to prove the effects of medications, guinea pigs weighting 200~300 gm were exposed to 112~114 dB of 4,000 dB pure tone for 4 hours to induce noise trauma. They were treated with A.T.P. and niacin for 4~5 weeks. And then, sacrified them to examine the extend of inner hair cell damage. We compared them with control group. The following results were obtained. 1) In Preyer's reflex, A.T.P. treated group was all positive, but control group was positive in one animal among four animals. 2) Damage of hair cells in basal turn was no significant change in all groups. 3) In A.T.P. and niacin treated groups, damage of hair cells in other turns were less severe than control group. 4) In niacin treated group, damage of hair cells was relatively mild.