An external nasal dilator (Breathe Right, CNS, Inc., Bloomington, MN) has become popular with athletes. The dilator is an adhesive band with a central elastic strip. When applied across the nasal valve, the device theoretically increases nasal valve area. We used acoustic rhinometry (Hood Laboratories, Pembroke, MA) to measure the cross-sectional area at the nasal valve with and without the device in 53 athletes. Thirty athletes were exercised on a cycle ergometer with and without the device while measuring physlologic parameters, including oxygen consumption (VO2), heart rate, and respiratory rate. The study was conducted in a randomized, double-blind, placebo-controlled manner. At rest, the external nasal dilator was found to significantly increase nasal valve area in all demographic groups measured. The device was also found to significantly decrease submaximal exercise perceived exertion, heart rate, ventilation, and VO2 when compared with placebo.