To clarify how cold weather may induce bronchoconstriction in patients with COPD, a series of challenges were performed in 20 patients with COPD in stable condition as well as in 13 healthy subjects. A whole-body exposure to -17 degrees C during resting nasal breathing was performed to study the reflex effects of facial cooling on lung function. In addition, a near-maximal hyperventilation of cold air was performed in a warm room to study the direct airway effects of cold air. The whole-body exposure to cold air induced statistically significant bronchoconstriction in both groups, the maximal decrements in FEV1 being 9.4 +/- 1.4% in the patients with COPD and 10.3 +/- 0.8% in the healthy subjects (p = NS). The whole-body exposure to cold air also increased the resting ventilation. The hyperventilation challenge induced bronchoconstriction only in the patients with COPD, the maximal decrements in FEV1 being 8.0 +/- 1.3% and 1.5 +/- 1.0%, respectively (p < 0.01). These results suggest that cooling of the facial skin is predominantly responsible for the bronchoconstriction due to cold weather both in patients with COPD and in healthy subjects. At high ventilation level, as during heavy exercise, the direct airway effects of cold air may also contribute to the bronchoconstriction in patients with COPD. Some patients with severe COPD might benefit from wearing protective clothing over their face in cold weather.