The effects of renal impairment on the pharmacokinetics of ceftriaxone in humans were examined after intravenous infusion of a 1-g dose over 15 min to 30 renally impaired patients. The study included 12 dialysis patients and 18 patients with severe, moderate, or mild renal impairment. Plasma and, where appropriate, urine and dialysate samples were collected at predetermined times and analyzed for ceftriaxone by high-pressure liquid chromatography. The elimination half-life (group mean ranged from 11.7 to 17.3 h) and plasma clearance (group mean ranged from 529 to 705 ml/h) did not correlate linearly with creatinine clearance. The renal clearance and fraction of dose excreted unchanged in urine were related linearly, however weakly, with creatinine clearance. Ceftriaxone was not removed from plasma to a significant extent during hemodialysis. The half-life was prolonged twofold, the plasma clearance was lowered less than 50%, and the volume of distribution was relatively unchanged in renally impaired patients compared with young or elderly healthy subjects with normal renal function at an equivalent dose. Since these changes are moderate, adjustment in the dosage regimen of ceftriaxone for patients with impaired renal function should not be necessary when ceftriaxone dosage is 2 g or less per day (2 g every 24 h or 1 g every 12 h). It was reported that the elimination half-life of ceftriaxone is substantially prolonged in a small percentage of patients with end-stage renal disease maintained on hemodialysis. Therefore, plasma concentrations of ceftriaxone should be monitored in dialysis patients to determine whether dosage adjustments are necessary.