We studied the effect of cricoid pressure and lateral tilt on airway patency during ventilation by facemask in a simulated obstetric setting. The lungs of 50 patients were ventilated by facemask and Guedel airway using a Nuffield Penlon 200 ventilator and Bain system with standard settings. Expired tidal volumes and peak inspiratory pressures were recorded for 10 breaths in each of four combinations: supine with no cricoid pressure, supine with cricoid pressure, 15 degrees lateral tilt with no cricoid pressure and 15 degrees lateral tilt with cricoid pressure. The timing of cricoid pressure was randomised and blinded to all observers. In both supine and tilted positions, cricoid pressure produced a reduction in tidal volume (p < 0.001) and an increase in peak inspiratory pressure (p < 0.001). Cricoid pressure with lateral tilt did not produce any additional airway obstruction to that in the supine position. Complete airway obstruction (tidal volume < 200 ml) resulted on three occasions, all with cricoid pressure applied.