The author participated in two prospective studies of patients receiving aminoglycoside antibiotics. In the first study, 54 patients received amikacin, and 54 received gentamicin. In the second study, 61 patients received gentamicin, 50 received netilmicin, and 52 received tobramycin. The studies were randomized and the investigator was blinded when evaluating auditory and vestibular toxicity and nephrotoxicity. All patients had pure tone audiometric evaluations, and two thirds of the patients had vestibular function tests consisting of an electronystagmogram performed with 30 degrees C and 44 degrees C water. Nephrotoxicity was measured by changes in serum creatinine levels. The incidence of gentamicin toxicity in the first study was 11 per cent, and it was 18 per cent in the second study. Amikacin was ototoxic 12.9 per cent of the time, whereas the incidence of tobramycin ototoxicity was 11.5 per cent, and the incidence of netilmicin ototoxicity was 2 per cent. Cases of unilateral, delayed-onset, and reversible auditory and vestibular toxicities were seen in all drug treatment groups. Nephrotoxicity was rare with amikacin usage. Gentamicin, on the other hand, produced a 18.6 per cent, tobramycin a 25 per cent, and netilmicin a 21.3 per cent rate of nephrotoxicity.