The sensitivity and reliability of the FEF end-tidal CO2 detector were investigated for its suitability in the assessment of correct placement of an endotracheal tube. Sensitivity was determined by having eight blinded volunteers observe the color change in the FEF detector with the administration of different volumes and varying CO2 concentrations of gas mixture. The color change in the FEF detector was also assessed during esophageal ventilations before and after administration of carbonated beverage into the stomach of swine and during cardiopulmonary resuscitation in swine. An interpersonal variation was present among the blinded observers during the color-matching process. Different colors were observed with the same volume and CO2 concentration of gas mixture. During esophageal ventilations before or after the administration of carbonated beverage, the FEF detector was neither accurate nor rapid in identifying esophageal placement of the endotracheal tube. The "C" color was displayed during the initial six ventilations in one swine, and esophageal intubation would have been missed. The FEF detector could (by displaying a "C" color) identify one of six correctly intubated swine during cardiopulmonary resuscitation. In conclusion, the FEF CO2 detector does not have the characteristics to reliably assess the correct placement of an endotracheal tube.