OBJECTIVE To assess renal safety of sevoflurane administered to Wistar rats at clinical concentrations during prolonged periods of inhalation. METHODS The experimental animals were assigned to two groups of six rats each. Group I received anesthesia with 1.5% sevoflurane for 6 hours and group II received the same concentration of sevoflurane for 15 hours. The anesthesia was inhaled in an open circuit of fresh air at 1 l/min (medicinal air, 22.75% O2). The animals were kept in metabolic cages throughout the nine days the experiment lasted. Weight and urine output were recorded daily and the day before anesthesia was started, inorganic fluoride and blood was analyzed for renal function (urea, sodium, and blood urea nitrogen [BUN]). Between two and three hours after withdrawal of anesthesia, inorganic fluoride was again assessed, and on the last day of the experiment a new blood sample was taken to evaluate renal function. Kidney tissue was then studied. RESULTS The two groups were similar as to weight, urea, sodium and BUN. Hourly diuresis was significantly greater after anesthesia in group II but not in group I. Inorganic fluoride was significantly higher in both groups, with postanesthetic levels of 22.42 +/- 1.76 microM/l in group I and 35.05 +/- 1.80 microM/l in group II. Renal tissue from both groups appeared normal under an optical microscope. CONCLUSIONS Sevoflurane at the doses tested increases inorganic fluoride concentrations although for both periods the levels stayed under 50 microM/l, which has been considered the nephrotoxic threshold. No signs of changes in renal function were observed in blood texts or tissue studies.