The safety, pharmacokinetics and efficacy of one daily injection (qd) of amikacin (AK) and netilmicin (NT) was compared with the recommended schedules (cs), i.e. twice-daily or thrice-daily, respectively. Women (17–43 years, n = 78) suffering from pelvic inflammatory disease were randomly assigned to qd or cs of either AK (14 mg/kg per day) or NT (6.6 mg/kg per day). Biometric parameters were similar in the 4 groups and all patients recieved ampicillin (4 g/day) and tinidazole (0.8 g/day). The Repeated Measures Analysis of Variance was used to distinguish the effects of the schedules and of the drugs choice on critical parameters. Efficacy was similar in the 4 groups and not influenced by the schedule of administration. No significant differences in nephro-and oto-toxicity were observed as assessed by serum creatinine and losses of hearing at low frequencies, but early phospholipiduria and auditory losses at high frequencies were significantly reduced with the qd administration compared to cs and by AK compared to NT. These data suggest that the qd schedule of AK and of NT is as efficacious as their cs schedules, and causes less renal and auditory alterations.