Performance of mask-bag ventilation was evaluated on an infant resuscitation mannequin to resolve uncertainty regarding the proficiency of pediatric resuscitation personnel in this technique and to determine whether the type of resuscitation bag used would affect performance. Performance using a self-inflatable resuscitation bag was generally adequate. Forty-six of 50 operators achieved an adequate minute ventilation, and 48 of 50 operators achieved a mean tidal volume exceeding that of the mask plus simulated physiologic dead space. Wide variation with a tendency to hyperventilate and to use excessive pressures indicate the need for improved standard training methods. Technical difficulties with an anesthesia bag impaired performance, suggesting that only self-inflatable bags should be used for mask-bag ventilation during pediatric resuscitation, unless the staff's proficiency with anesthesia bags is clearly demonstrated.