In 26 stable patients with chronic obstructive pulmonary disease, tidal expiratory flow-limitation (TEFL), inspiratory capacity, breathing pattern and dyspnea sensation were assessed during air and heliox (20% O(2) in He) breathing at rest and during exercise up to 2/3 maximal work rate. Breathing air, the 13 patients with TEFL at rest remained flow-limited also during exercise, while 7 of the non-flow-limited patients became flow-limited; tidal volume increased more in non-flow-limited patients, whereas inspiratory capacity decreased in flow-limited and increased in the non-flow-limited patients. Heliox did not abolish flow-limitation, had no effect on breathing pattern, reduced exercise dynamic hyperinflation in 25% of the flow-limited patients, depending on the degree of the dynamic hyperinflation on air, and lessened dyspnea sensation in all patients. Hence, the presence of TEFL has no systematic effects on the respiratory response to heliox, and the heliox-induced decrease of exercise dyspnea is not mainly due to changes in dynamic hyperinflation or TEFL.