Although pulse oximeters have been proven accurate in the prehospital environment, they have not been proven to be necessary. This study was undertaken to determine if emergency medical services (EMS) providers can identify hypoxemia without pulse oximetry. An oximeter was placed at the ambulance entrance to the emergency department (ED), and EMS personnel obtained saturation levels on all patients on arrival. Hypoxemia was defined as a saturation level of 95% or less. The hypoxemia was classified as "recognized" if the patient received aggressive intervention and "unrecognized" if the patient did not. One hundred eighty patients were enrolled in the study; 30 had a saturation level of 95% or less. Twenty-seven (90%) of those patients had "unrecognized" hypoxemia. Twenty-three (85.2%) of the 27 patients with "unrecognized" hypoxemia did not complain of respiratory distress. Thus, there are patients whose hypoxemia is unrecognized by EMS providers, and this occurs most frequently in patients who do not complain of respiratory distress.