In the present paper, we report data on the possible genotoxic properties of two inhalation anaesthetics - sevoflurane (SVF) and isoflurane (ISF) - in peripheral blood lymphocytes of patients before, during and after anaesthesia as compared to an unexposed control group. Both anaesthetics were evaluated for genotoxic activity using the comet assay. The exposed groups consisted of 24 ASA grades 1-2 unpremedicated patients (aged 20-66 years, anaesthetized 115-162 min for elective lower abdominal surgery), while the control group consisted of 12 healthy individuals. After induction of anaesthesia (thiopenthone sodium 5-7 mg/kg, fentanyl citrate 0.1 mg and vecuronium bromid 0.1 mg/kg), anaesthesia was maintained with inhalation of SVF 1-1.5% (n = 12) or ISF 1-1.5% (n = 12) in oxygen-air mixture. Venous blood samples were obtained before the induction of anaesthesia, at 60 and 120 min of anaesthesia and on the first, third and fifth days following anaesthesia. The comet assay detects DNA damage which includes strand breaks and alkaline labile sites induced directly by genotoxic agents as well as DNA degradation due to cell death. One hundred cells from each sample were examined and graded as no tailed, short and long tailed nuclei. The mean comet response was not different between controls and patients before anaesthesia. However, similar significant increases were observed in the mean comet response in blood sampled from patients at 60 (36.5 +/- 11.2, 37.8 +/- 12.1), or 120 min (53.1 +/- 17.1, 50.0 +/- 12.2) of anaesthesia and on the first day (37.8 +/- 15.1, 35.2 +/- 15.7) after anaesthesia in SVF and ISF treated groups, respectively. Removal of the DNA damage was observed after the third day of anaesthesia and the repair was completed within 5 days. The DNA damage detected in lymphocytes of patients during anaesthesia with SVF or ISF showed similar results as demonstrated by an increased mean comet migration at 120 min of anaesthesia and the cells were able to repair the induced DNA damage completely on the fifth postoperative day. (C) 2001 Elsevier Science B.V. All rights reserved.