The ototoxic damage that drugs such as neomycin, kanamycin, colistin, cisplatin, transplatin and carboplatin cause on outer and inner hair cells in postnatal day 3 rat cochlear explants was investigated. Phalloidin-fluorescein conjugate-stained stereocilia bundles of sensory hair cells were quantified by video image analysis as a measurement of ototoxic effect. The video image quantification system established dose-response curves for ototoxic drugs (e.g. calculation of an IC 5 0 ) and allowed comparisons between several ototoxins from the same family. This methodology provided the means to assess the efficacy of otoprotectant agents in preventing ototoxicity. Poly-l-aspartate (10 - 5 m) and poly-l-glutamate (10 - 5 m) protected auditory hair cells from neomycin (10 - 3 m) toxicity while reduced glutathione (10 - 3 m) provided protection against cisplatin (10 - 4 m)-induced hair cell damage.