A prospective clinical trial was conducted at a level I trauma center to assess the efficacy of end-tidal carbon dioxide (CO2) detection in four groups of patients requiring emergency intubation because of cardiac arrest, major trauma, respiratory failure, or the need for airway protection. A semiquantitative, colorimetric FEF end-tidal CO2 detector (Fenem, Inc, New York, NY) was used to evaluate endotracheal versus esophageal intubation. This disposable, bedside detector registers three ranges of CO2 concentration: "A" (purple) indicates low levels and probable esophageal intubation; "B" (beige) indicates moderate levels and probable tracheal intubation with hypocarbia; "C" (yellow) indicates high levels and tracheal intubation. Clinical observation, patient response, chest x-ray films, and arterial blood gas results were used to corroborate placement of the endotracheal tube. The FEF detector was found to be 100% reliable for confirming tracheal placement when registering levels in the B and C ranges and 100% reliable for detecting esophageal intubation when registering levels in the A range. In conclusion, the FEF CO2 detector is a reliable and useful adjunct for airway management of diverse groups of patients in the emergency setting.