The demands for an optimal ventilation apparatus are that it can be easily handled, achieves a sufficiently high ventilation volume, and minimizes gastric inflation. Our aim was therefore to carry out a study in a training mannikin to find out whether the Oxylator EM100, compared with the bag, obtains improved ventilation and a decrease in gastric inflation. In a randomized crossover study, 72 subjects were selected (24 physicians, 44 nurses and 4 auxiliary nurses), chosen from the operating theatre, emergency department and intensive care unit of two hospitals. We used the Ambu-Bag Mark III with mask No. 4, the Oxylator EM100 with a pressure setting of 35 cm H2O run in the manual setting, the Ambu-Man C mannikin as well as the Ambu-CPR computer program. The resuscitation cycles of the standard two-rescuer's adult procedure lasted 3 min each, with a 3-min pause between the crossover procedure. The participants could improve their ventilatory volume with the Oxylator EM100 by 635 ml (95% confidence interval 578-692 ml) compared with the bag ventilation. The number of subjects who could attain a mean ventilatory volume of 800 ml or more increased from 15% to 98.6% (P < 0.001). Compared with the bag, the increase of adequate respirations (> or = 800 ml) obtained by the Oxylator EM100 for the individual participants amounted to a median of 91% (P < 0.001). Moreover, conventional ventilation caused in 42% one or several instances of gastric inflation, whereas no such reactions occurred with the Oxylator EM100. The Oxylator EM100 showed significantly better results in the mannikin than the bag. Of most importance is a significant lowering of gastric inflation and less so a marked increase in ventilatory volume. Our trial procedure with a relatively high lung compliance and a high oesophageal sphincter opening simulated favorable conditions. Owing to a large in vivo variability of these magnitudes, a direct testing in real patients with circulatory arrest is indicated.