Anaesthetics, like Sevofluran^®, are widely used in the daily medical routine. While the patient should be painless and unconscious, basic live maintaining functions like the respiratory drive should not be impaired. We used the perfused heart-brainstem preparation of rats (21d and older), we recorded the respiratory activity via a suction electrode placed at the nervous phrenicus (NP). Sevofluran^® at a concentration range between 1 nM and 1 mM was applied via the perfusion system. Analysed were changes of the frequency of phrenic discharges before and after the application in 15 preparations. Sevofluran^®concentration dependently increased the frequency of NP discharges with a threshold concentration of 1 nM (38±15 % increase). At a concentration of 100 nM the frequency was 75±12 % increased compared to the control value. While during the application the frequency increased, the regularity of the discharges decreased in two different ways: 1.- the amplitude of the NP discharges varied, and 2.- the expiratory phase had intervals between 3.8+4 seconds at a concentration of 1 mM compared to 10.3±2.5 seconds under control conditions. The anaesthetic Sevofluran^® did not suppress respiratory activity, but the activity was less regular, which might be an important observation in regard to its daily use as an anaesthetic.