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Background: Respiratory depression, such as obstruction of upper airway and inadequate ventilation, often appears during sedation and anesthesia. We studied the effect of propofol on the upper airway patency and the inspiratory drives., Methods: Experiments were performed on the adult rabbits vagotomized, paralyzed and ventilated with nitrous oxide-oxygen-sevoflurane. We evaluated and compared depressant effect of propofol on the peak amplitude of both hypoglossal nerve (AMP-HG) and phrenic nerve (AMP-PH) activities, inspiratory time (Ti), expiratory time (Te) and respiratory cycle (Tc)., Results: Bolus injections of propofol transiently reduced AMP-HG more than AMP-PH (18 and 70% of control, respectively). But AMPs returned to the control levels about 10-15 min after the injection. For 0.5 mg.kg-1.min-1 continuous infusion, propofol soon began to reduce both AMPs. AMP-HG was reduced to about 20% and AMP-PH to 60% of control. Administration of propofol with 1.0 mg.kg-1.min-1 caused more reduction in AMPs with respiratory slowing and AMP-HG disappeared in some animals., Conclusion: During the sedation with low dose of propofol, we need to pay attention to potential upper airway obstruction. In addition to the above, high doses of propofol could reduce spontaneous inspiratory drive, and we need to keep both upper airway patency and sufficient ventilation.