Using the Stephens anaesthetic apparatus-which is a closed system with an in-circuit, nonprecision vaporizer-and isoflurane as anaesthetic gas, 18 rabbits were anaesthetized and showed sufficient hypnosis, analgesia, and muscle relaxation during bone surgery. Induction of anaesthesia was achieved with intravenous propofol and all rabbits were intubated afterwards. During the following isoflurane inhalation anaesthesia the mean arterial blood pressure decreased considerably (compared to control measures before induction), the heart rate remained the same or showed a slight increase, and the respiratory rate decreased. The arterial pO2 decreased corresponding to the respiratory depression after propofol induction and increased again during spontaneous ventilation with 100% oxygen. The changes in arterial pCO2 and pH were representative for a rise in the CO2-stimulation threshold. A moderate metabolic acidosis could be seen due to preanaesthetic excitement of the animals. Recovery time was short (between one and 11 minutes) and no signs of excitation could be detected. The consumed volume of isoflurane was 0.80 ml/kg BW/h.