We compared maintenance of anaesthesia and recovery using either sevoflurane or enflurane anaesthesia in ASA I-III patients undergoing surgery with an anticipated minimum duration of 3 h. Serum fluoride concentrations were also measured to assess the potential for renal toxicity. After induction of anaesthesia with thiopentone, patients received, for maintenance, either 1.5% end-tidal sevoflurane (0.73 MAC) with N2O 58% (0.58 MAC) (n = 40) or 1.2% end-tidal enflurane (0.7 MAC) with N2O 57% (0.57 MAC) (n = 40). Other drugs administered during anaesthesia were similar in all groups. Haemodynamic measurements, recovery times, as well as post-operative nausea and vomiting were comparable in both groups. The mean peak plasma inorganic fluoride ion concentrations were reached 4 h after operation in both groups (27.7 microM L-1 for sevoflurane and 16.75 microM L-1 for enflurane, P < 0.05) declining 50% within 24 h in both groups. A positive correlation (P < 0.05) was found between anaesthetic exposure (MAC h) and fluoride concentrations in the two groups. Sevoflurane anaesthesia resulted in similar haemodynamic stability, recovery times and post-operative side effects as enflurane anaesthesia, but produced significantly greater serum fluoride levels.