The pharmacokinetics of intravenously administered netilmicin, an investigational aminoglycoside antibiotic, were studied in 38 patients with creatinine clearance ranging from 150 to Oml/min/1.73m2 in order to determine the influence of kidney function status on the disposition of the antibiotic. The serum disappearance of netilmicin followed first order kinetics and the elimination rate constant decreased proportionally with decreasing renal function. Half-lives averaged 2.2 hours in normal individuals (creatinine clearance greater than 80ml/min/1.73m2) and reached 42 +/- 10 hours (mean +/- SD) in virtually anephric patients. The elimination rate constant lowered proportionally with decreasing renal function. Several linear relationships between pharmacokinetic parameters and renal function indicators were defined. A clinically useful correlation indicates that the half-life may be approximated as 3 times the serum creatinine concentration and may be used for adjustment of dosage of netilmicin in the treatment of patients with impaired renal function. During haemodialysis, netilmicin extraction from the blood reaches 75 +/- 14% (mean +-/ 95% confidence interval) of that of creatinine and 88 +/- 19% of that of blood urea nitrogen.