Our aim was to compare the hepatotoxic effects of two different concentrations of sevoflurane. Thirty male New-Zealand rabbits were devided into three groups of ten: Group I, consisting a control group; study group II, which was anaesthetized with sevoflurane at 2.5%, and study group III at 4.0%. These two groups were anaesthetized at their assigned concentrations for one hour per day, every other day for one week; each group receiving a total of three anaesthetics. After the first week, each study group was anaesthetized for only one hour per week, for a total of eight weeks. Baseline blood samples were obtained from the awake animals, after that samples were collected at 48 hours after each anaesthetic administration for the study's duration. Measurements included serum electrolytes and protein electrophoresis, and serum enzymes. Forty-eight hours after the last exposure of sevoflurane, blood samples were collected, and the animals were sacrificed and exsanguinated, and postmortem examinations were performed. Samples of kidney and liver were prepared for histopathologic examination, and were also evaluated by transmission electron microscopy. Enzyme concentrations were significantly increased in two study groups. In Group II, all the increased serum enzymes returned nearly to baseline values by week 5. In Group III, the aspartate aminotransferase concentrations remained elevated during the study period, and the other enzymes returned nearly to baseline values by week 5. The alkaline phosphatase concentrations were decreased especially in Group III. In both groups, serum albumin levels were decreased for the 2nd and 3rd weeks of the study. Also serum electrolytes were increased especially in Group III. The kidney slides showed regenerative changes in the study groups. In the liver slides there was cellular edema, hydropic degeneration and focal hepatocellular necrosis. Also inflammatory infiltration was noticed in portal areas and parechymal areas. Sevoflurane administrated at 2.5% and 4.0% concentrations for 11 hours during an 8 week period may disturb hepatocellular integrity, and these findings suggest a probability of hepatotoxicity.