Cold air hyperventilation is an indirect challenge (cold air challenge, CACh) with high specificity and low sensitivity in defining asthmatic subjects. A small proportion of chronic obstructive pulmonary disease (COPD) patients present with positive CACh. The aim of this prospective study was to investigate the presence of factors related to cold air challenge (CACh) in COPD patients. Factors examined were FEV(1), FEV(1)/FVC, reversibility after bronchodilation, eosinophils in induced sputum, bronchial hyperresponsiveness to methacholine and the spirometric response to tiotropium compared to placebo. We studied 92 consecutive COPD patients in order to retrieve 15 CACh positive + patients. Fifteen COPD patients with negative CACh [CACh(-)], randomly selected from the initial group, were added in order to retrieve a group of 30 patients. Spearman's correlation coefficient was used in order to evaluate possible significant correlations between CACh values and study parameters. Sixteen percent of our subjects presented CACh+. CACh values were repeatable with an intraclass correlation coefficient between the two measurements 0.980 (95% CI 0.940-0.993). The only significant correlation observed was between Delta FEV(1) after CACh [Delta(C)FEV(1)] and trough FEV(1) values post tiotropium inhalation (r(2) = 0.62, p < 0.0001). When we analyzed the response to tiotropium in the 2 separate groups we found that patients with CACh+ presented significantly lower values of trough FEV(1) compared to those with CACh(-). In conclusion, a small proportion of COPD patients present with bronchial hyperresponsiveness to CACh. The only parameter related to CACh + in our study was a smaller bronchodilating effect of tiotropium.