BACKGROUND: This multicenter study was undertaken to compare the effect of sevoflurane with that of isoflurane on renal function in 26 patients with pre-existing renal insufficiency. Sevoflurane undergoes hepatic metabolism, with release of inorganic fluoride. Elevated fluoride levels have been associated with renal impairment in patients undergoing methoxyflurane anesthesia raising concerns about the nephrotoxic potential of sevoflurane. METHODS: Patients were ASA II or III class, with renal insufficiency defined by a preoperative serum creatinine concentration of 1.5-3.0 mg/dl. A standardized anesthetic regimen was used consisting of intravenous induction with propofol, vecuronium for muscle relaxation, and fentanyl for analgesia. Patients were randomized to receive either isoflurane or sevoflurane with 100% oxygen. Blood samples were obtained preoperatively and at 24, 48, and 72 h postoperatively for renal/electrolyte determinations. Blood samples for plasma fluoride measurement were obtained preoperatively. RESULTS: Plasma fluoride levels were significantly higher in patients receiving sevoflurane at all measurement points from 0 to 72 h postanesthesia. Mean peak fluoride concentration was 33.4 µM. The maximum fluoride value measured was 51.2 µM. There were no significant differences in postoperative serum creatinine values at any time between patients receiving sevoflurane or isoflurane. CONCLUSIONS: Sevoflurane metabolism produces elevations in plasma fluoride concentrations relative to isoflurane. Despite the increase in plasma fluoride levels, the administration of sevoflurane to patients with renal insufficiency did not produce any adverse effects on renal function as measured by serum creatinine concentration when compared with isoflurane.