Experiments were performed on guinea pigs to assess the eventual ototoxic side effects of a new glycopeptide antibiotic called teicoplanin. For a better validation, in the same study other animals were treated with tobramycin, a well known ototoxic antibiotic of the aminoglycoside family, and a group of control animals was also constituted. Antibiotic treated animals were injected with the high dose of 90 mg/kg/day during 21 consecutive days. Electrophysiological measures of equilibrium and acoustic functions were taken and morphological evaluations of the cochleas were performed. The results indicate that in these animal experiments teicomycin appears to be clearly toxic for the vestibule and the cochlea.