Using posterior rhinomanometry, we measured nasal airflow resistance (Rn) and flow-resistive work of nasal breathing (WONB), with an external nasal dilator strip (ENDS) and without (control), in 15 healthy adults (6 men, 9 women) during exclusive nasal breathing and graded (50-230 W) exercise on a cycle ergometer. ENDS decreased resting inspiratory and/or expiratory Rn (at 0.4 l/s) by >0.5 cmH₂O · l¹ · s in 11 subjects ("responders"). Inspired ventilation (I) increased with external work rate, but tended to be greater with ENDS. Inspiratory and expiratory Rn (at 0.4 l/s) decreased as I increased but, in responders, tended to remain lower with ENDS. Inspiratory (but not expiratory) Rn at peak nasal airflow (n) increased as I increased but, again, was lower with ENDS. At a I of ~35 l/min, ENDS decreased flow limitation and hysteresis of the inspiratory transnasal pressure-flow curve. In responders, ENDS reduced inspiratory WONB per breath and inspiratory nasal power values during exercise. We conclude that ENDS stiffens the lateral nasal vestibule walls and, in responders, may reduce the energy required for nasal ventilation during exercise.