Plasma inorganic fluoride concentrations were measured in adult patients without hepatic or renal disease following sevoflurane-N2O anesthesia (n = 7) or enflurane-N2O anesthesia (n = 6). The anesthetic dosage of sevoflurane and enflurane was 6.48 +/- 2.15 %-hours and 6.57 +/- 2.50 %-hours, respectively. The mean peak plasma inorganic fluoride concentration in the sevoflurane group was 19.5 +/- 13.4 mumol/L 1 hour after anesthesia, which decreased to preanesthetic levels 24 hours after anesthesia. In the enflurane group the values were 13.2 +/- 5.8 mumol/L at the end of anesthesia and decreased, but remained, still twice as high as the preanesthetic level 24 hours after anesthesia. The relationship of plasma inorganic fluoride concentration and anesthetic dosage was more pronounced in the sevoflurane group (r = 0.68, slope = 4.2) than in the enflurane group (r = 0.39, slope = 1.2). In conclusion, sevoflurane-N2O anesthesia results in similar subnephrotoxic levels of plasma inorganic fluoride as enflurane-N2O anesthesia, and although the fluoride concentration had a better correlation to anesthetic dosage in the sevoflurane group than in the enflurane group, its excretion was faster in the sevoflurane group than in the enflurane group.