Serum and urinary concentrations of inorganic fluoride were measured before and after sevoflurane anesthesia in 10 patients without renal disease, who were scheduled for surgery lasting 13.4 +/- 0.9 h (mean +/- SE). The mean concentration of serum inorganic fluoride reached a maximal value of 42.5 +/- 4.5 mumol/L at the end of anesthesia. However, 5 of 10 patients had serum inorganic fluoride concentrations that exceeded 50 mumol/L (i.e., the nephrotoxic dose). A positive correlation was found between serum inorganic fluoride concentration and anesthetic dose. The largest urinary excretion of inorganic fluoride was 1804 +/- 378 mumol/day in the first postoperative day and rapidly decreased thereafter. We concluded that lengthy sevoflurane anesthesia created serum inorganic fluoride concentrations that could influence renal function, although nephrotoxicity was not demonstrated in our biochemical study.