The elimination kinetics of aztreonam (SQ 26, 776), a new, completely synthetic, monocyclic &bgr;-lactam antibiotic, were studied after the administration of a single 1g intra-venous dose. Five healthy volunteers and 20 patients with various degrees of renal insufficiency were enrolled in this study. Concentrations of aztreonam in serum and urine were determined by both microbiological and high pressure liquid chromatography (HPLC) assays.The pharmacokinetic parameters for aztreonam were calculated on the basis of a 2-compartment open model. Serum concentrations of aztreonam at 10 minutes after administration were approximately 100 &mgr;g/ml in all subjects, regardless of renal function (HPLC assay). The mean serum half-life during the &agr;-phase showed no important variation with renal function. The mean serum half-life during the &bgr;-phase was 1.8 hours in normal subjects and 8.4 hours in haemodialysis patients (HPLC assay). There was a linear correlation between the serum clearance of aztreonam and creatinine clearance.The mean cumulative urinary recovery of aztreonam in 48 hours was 60 to 70% of the administered dose in normal subjects but this was reduced in the presence of renal insufficiency. SQ 26,992, the microbiologically inactive metabolite of aztreonam resulting from hydrolytic opening of the &bgr;-lactam ring, was undetectable in the serum of normal subjects but was found in low levels in uraemic patients. Half of a 1g intravenous dose of aztreonam was eliminated during 4 hours of haemodialysis.Guidelines for administration of aztreonam in the presence of renal failure are given.