Patients with serious systemic infections admitted to eight medical centers in six Asian countries were treated with 300 mg of netilmicin given once daily (group A: 92 patients) or 100 mg of netilmicin given three times daily (group B: 93 patients). Netilmicin was administered by intramuscular injection or slow intravenous infusion until clinical, laboratory, and bacteriologic measures were normalized and for not more than two additional days. A clinical cure was achieved in 88% of the patients from group A and in 68% from group B. The causative micro-organisms were eliminated or infection site healed in 90% of group A and in 88% of group B. The mean treatment duration was 6.9 days in group A and 8.8 days in group B. Two patients in each group developed symptoms of nephrotoxicity; the pretreatment serum creatinine levels in all four patients were in the high borderline range. No other serious side effects were found. It is concluded that netilmicin administered once daily is safe and more effective than netilmicin administered three times daily.