46 measurements of lactate during aorto-femoral bypass-operation were performed under epidural analgesia, halothane- and neurolept anaesthesia. Independent of the metabolic parameters a significantly higher lactate rate was found under halothane anaesthesia than in the two other groups even though - at the same perfusion volume in all three groups - a significantly lower arterial mean pressure and peripheral resistance was measured under halothane- and epidural anaesthesia than under neurolept anaesthesia. The authors come to the conclusion that under aorto-femoral bypass operations a moderate hypotension can be carried out even in patients, showing arterio-sclerotic changes of the vessels, without a significant influence on metabolism.