Abstract Objective—To determine the effect of a commercially available nasal strip on airway mechanics in exercising horses. Animals—6 horses (5 Standardbreds and 1 Thoroughbred). Procedure—Horses exercised on a treadmill at speeds corresponding to 100 and 120% of maximal heart rate with and without application of a commercially available nasal strip. Concurrently, tracheal pressures, airflow, and heart rate were measured. Peak inspiratory and expiratory tracheal pressures, airflow, respiratory frequency, and tidal volume were recorded. Inspiratory and expiratory airway resistances were calculated by dividing peak pressures by peak flows. Endoscopic examination of the narrowest point of the nasal cavity (ie, nasal valve) was performed in 1 resting horse before, during, and after application of a nasal strip. Results—During exercise on a treadmill, peak tracheal inspiratory pressure and inspiratory airway resistance were significantly less when nasal strips were applied to horses exercising at speeds corresponding to 100 and 120% of maximal heart rate. Application of the nasal strip pulled the dorsal conchal fold laterally, expanding the dorsal meatus. Conclusions and Clinical Relevance—The commercially available nasal strip tented the skin over the nasal valve and dilated that section of the nasal passage, resulting in decreased airway resistance during inspiration. The nasal strip probably decreases the amount of work required for respiratory muscles in horses during intense exercise and may reduce the energy required for breathing in these horses. (Am J Vet Res 2002;63:1101–1105)