The pharmacokinetics of cefuroxime axetil (RS3 formulation) were studied in 20 elderly patients following admission for lower respiratory or urinary tract infection. The mean age was 83.9 years. A 12-hourly dose of 250 mg was given for five days. The mean time to attain maximum serum concentration was 3.2 h with a mean peak concentration of 8.5 mg/l. The mean serum elimination half-life was 3.5 h and the AUC0-infinity 60.4 mg/h.l. There was no accumulation of the drug in the patients studied after five days treatment. The data suggest that the standard dosage regimen is adequate in the sick elderly patient.