The ototoxicity and nephrotoxicity of aminoglycoside antibiotics (dibekacin, gentamicin and kanamycin) administered to rabbits by rapid intravenous or intramuscular injections were histopathologically compared. Comparative evaluations between the two routes were further made concerning the levels of the antibiotics in serum and in perilymph. The results revealed that, although the peak serum level after a rapid intravenous injection was significantly higher than that observed after an intramuscular injection, no differences in the transfer into the perilymph, and in inner ear or renal damage were seen between the two different routes. In other words, the results of the present study did not support the conventional idea that the higher the peak blood levels of the aminoglycoside antibiotics, the greater the risk of damage to the inner ear or kidney.