The effects of anticholinergic agents or long acting beta(2)-agonists on exercise capacity in chronic obstructive pulmonary disease (COPD) improves various out come measures but there is not enough double-blind study which included comparison of different medications. The aim of this study was to compare the effect of ipratropium bromide and formoterol on exercise capacity and also to determine the relationship between this improvement in functional parameters and exercise capacity for each treatment in patients with COPD. This study was performed as randomized, double blind and two period crossover design. Ten volunteer stable COPD patients were recruited from outpatient COPD clinic. At the initial visit medical data were recorded. One week later baseline measurements; pulmonary function tests and cardiopulmonary exercise testing were performed, afterwards, patients received ipratropium bromide 40 microg four times a day or formoterol 12 microg two times a day for two weeks. After a washout period, medications were crossed for another two weeks. After each of treatment period, all tests were performed. Nine subjects were male and mean age was 51.1 +/- 5.45 years, all of them were heavy smokers, level of COPD was mild to moderate (FEV(1)= 69%, FEV(1)/FVC= 68%). While formoterol significantly improved FEV(1), FEV(1)/FVC %, ipratropium significantly improved FEV(1), FEF(25-75), peak oxygen uptake and minute ventilation. Moreover, both of the medications increased exercise time. There were no differences between effects of ipratropium bromide and formoterol on exercise capacity and functional parameters. We observed that ipratropium bromide and formoterol have similar improvement in exercise capacity in COPD patients. The improvement in exercise capacity also correlated with increase in FEV(1).