Percutaneous transtracheal ventilation can be a lifesaving procedure when endotracheal intubation is not possible, but an understanding of the technique and necessary instruments is essential. This study, performed on adult sheep, defined the limited circumstances under which a 15-gauge needle, connected to oxygen at 50 pounds per square inch (psi), can provide an emergency transtracheal airway. There are situations, such as complete airway obstruction, when this combination is contraindicated. In addition, transtracheal ventilation might have to be performed using simpler equipment, such as a self-inflating resuscitation bag (AMBU-type) or with no equipment other than the transtracheal airway. A 3.0-mm I.D. cannula provided an adequate transtracheal airway under all circumstances examined. A 3.5-mm cannula is commercially available and physicians who deal with airway problems should be familiar with its use.