The hepatic effects of sevoflurane administered under different inspiratory oxygen concentrations were examined. Male rats pretreated with phenobarbital for 5 days and fasted for 24 hours were anesthetized with 2.4% sevoflurane administered under different oxygen concentrations (10%, 14%, 21% or 100%). The rats administered sevoflurane under 21% oxygen were used as the control. The amount of microsomal protein, the content and activity of hepatic microsomal enzymes, and the amount of enzymes released from the liver cells (GPT, OCT) of each group of rats were measured for 7 days after these procedures. The content of cytochrome P-450 and the activity of aminopyrine demethylation and aniline dehydration were decreased significantly to about 58%, 43% and 40% that of the control, respectively. Furthermore the plasma level of GPT and OCT was elevated to 1,107±620 IU/L and 422±270 IU/L respectively soon after sevoflurane anesthesia only in the group of rats administered sevoflurane under a 10% oxygen concentration. In this study, severe damage to the liver of the rats was observed after sevoflurane anesthesia under 10% oxygen following enzyme induction and fasting.