The external nasal dilator strip (ENDS) device (Breathe Right, CNS Inc., Chanhassen, MN, USA) has been adopted by athletes to promote nasal route breathing during exercise. We studied the influence of ENDS on the switching point from nasal-only to oro-nasal breathing during exercise in 4 healthy men (age 25 +/- 2 yrs, mean +/- SEM) and 5 women (age 30 +/- 5 yrs). Resting inspiratory nasal airflow resistance decreased from 0.33 +/- 0.02 kPa/L/s without ENDS to 0.22 +/- 0.01 kPa/L/s with ENDS (p < 0.01). ENDS delayed the onset of oro-nasal breathing such that the time from commencement of exercise to switching increased by 15.2%, and maximum levels of inspiratory nasal airflow and ventilation achieved prior to switching increased by 14.9% and 14.3%, respectively (all p < 0.05). We conclude that, in normal healthy subjects, ENDS does promote nasal route breathing during exercise, but any delay in the onset of oral route breathing during a progressive exercise task appears relatively small.