Pulse oximetry monitors have become so commonplace in acute health care settings over the last decade that blood oxygen is now considered a "fifth" vital sign. This study assessed the knowledge base related to pulse oximetry technology and clinical interpretation of the data given. A total of 68 participants--nurses, respiratory therapists, and resident physicians at a large general pediatric unit of a children's hospital--completed a survey of open-ended questions. Preliminary analysis revealed that 84% of the clinicians felt they received adequate training; 84% correctly identified what a pulse oximeter measured; 40% correctly identified how a pulse oximeter worked, but only 15% had a correct understanding of the oxyhemoglobin dissociation curve. Clinicians identified a wide range of normal arterial oxygen saturation values and made numerous errors in evaluating saturation readings in hypothetical clinical situations. Although the majority of pediatric staff felt well trained and knowledgeable about pulse oximetry, there was a lack of knowledge of basic principles. The results of this study have implications for basic professional education programs and the orientation and ongoing education of pediatric health care providers.