The effectiveness of gentamicin administered by the intranasal route in healthy human volunteers was studied. Thirty minutes after gentamicin in a solution of 1% sodium glycocholate was administered at 2 mg/kg of body weight, gentamicin concentrations of 2.48 +/- 0.42 mg/ml were present in the sera. Serum concentrations decreased to 0.94 +/- 0.13 mg/ml at 180 min. No serious side effects were observed. There was slight local irritation after a single dose. When administered intranasally without glycocholate, gentamicin was not present in the sera in detectable amounts.