A single 1.0-g dose of cefaclor administered to patients with stable end stage renal disease whose creatinine clearances were <5 ml/min produced a mean peak serum concentration of 48.3 +/- 19.8 mug/ml. The half-life was 2.3 +/- 0.3 h. Hemodialysis shortened the half-life of a similar dose to 1.6 +/- 0.3 h. Approximately one-third (340 mg) of the administered drug was recovered in the dialysate. Multiple doses of 500 mg every 6 h between hemodialysis sessions produced effective serum concentrations and no bioassay evidence of drug accumulation.