Adults patients scheduled for elective surgery were randomly allocated to receive preoxygenation with spontaneous breathing, positive pressure ventilation (positive inspiratory pressure: 12 cmH2O) without PEEP, and with PEEP (positive inspiratory pressure: 12 cmH2O, PEEP: 6 cmH2O). Preoxygenation time was measured from face mask positioning to FEO2=90% (FEO2 : expired fraction of O2). After endotracheal tube placement the time until SpO2=93% (SpO2 : peripheral oxygen saturation) was measured during monitored apnoea. Patient's discomfort was recorded (visual analogue scale).