Various techniques useful for the precise functional and morphological evaluation of the auditory and vestibular systems in the guinea pig are described. Their application in the comparative study of the ototoxicity of three aminoglycosidic antibiotics (gentamicin, tobramycin and dibekacin) administered at doses of 90 mg/kg/day for 20 consecutive days is presented. In these conditions a severe cochlear impairment was observed with gentamicin and tobramycin while it was minimal with dibekacin. Vestibular impairment was also severe with gentamicin and definite, although less important, with dibekacin and tobramycin.