In attempts to decrease gentamicin ototoxicity, the round windows of guinea pigs were covered with fat before gentamicin was given through the middle ear cavity. Although ototoxicity to the cochlea was reduced, the desired effect on the vestibular sense organs also was reduced, because of the oval window's resistance to drug penetration. In another series of guinea pigs, simple opening of the lateral semicircular canal and covering it with a pledget of Gelfoam soaked with gentamicin was an excellent method for producing a selective vestibular lesion. It is expected to reduce the function of all vestibular sense organs without impairing cochlear function.