Ear drops containing neomycin only rarely cause ototoxicity. The authors report on three patients with a tympanic membrane perforation who developed severe ototoxicity after use of eardrops containing 0.35 per cent neomycin. Mitochondrial DNA analysis revealed that there was no A1555G point mutation in these patients. This finding indicates that application of low concentration neomycin to the middle ear can cause severe inner ear damage even in humans who are not hyper-susceptible to aminoglycosides.