Seventy-six patients were included in a prospective study in order to assess the ototoxicity of netilmicin. Netilmicin. Netilmicin was administered intramuscularly with a dosage of 1.5 mg/kg body weight 2 or 3 times daily. The dosage was modified in cases with even slight renal insufficiency. Vestibular and auditory function was examined by electronystagmography (ENG) and audiometry before and during therapy, 1 week and 2-3 months after completion of therapy. Drug-related VIIIth nerve toxicity--vestibular dysfunction--was suspected in one case. However, this dysfunction was subclinical and reversible. The importance of pretreatment evaluation was obvious as an ototoxic damage might have been suspected in 14 patients if the pretreatment examination of vestibular and auditory function had not been performed. Clinical ototoxicity of netilmicin seems to be low when careful attention is paid to the renal function and the serum concentrations of the drug.