The purpose of our study was to determine whether anticholinergic and long-acting beta 2 agonist drug -mediated acute bronchodilator response of stable COPD patients can be detected by subjective (Borg dyspnoea scale-BDS) and objective (pulmonary function test-PFT) findings. We also investigated the difference in acute bronchodilator response mediated by these two drugs. BDS and PFTs were performed on 33 stable COPD patients before and after ipratropium bromide and formoterol medication. The difference in the effectiveness of these two drugs was compared. The BDS and all PFT parameters differed significantly after ipratropium bromide. The BDS and the RV/TLC decreased and the other parameters increased. After formoterol, the PFT parameters, except RV/TLC, increased and BDS decreased. While the Mean Inspiratory Capacity (IC) was 2167.88 +/- 731.63 (880-3460) ml. before medication, it increased to 2384.24 +/- 771.80 (1060-3650) ml. after ipratropium bromide. For formoterol, the Mean IC was 2107.58 +/- 738.39 (920-3490) ml. and 2311.82 +/- 759.24 (1060-3780) ml. before and after medication, respectively. Ipratropium bromide was found to be more potent in increasing IC than formoterol. No significant difference was found in terms of BDS and PFT parameters between the two drugs. It was concluded that an acute bronchodilator response in COPD can be detected by subjective and objective criteria. The increase in IC obtained by anticholinergic drugs is greater than that of a beta 2 agonist.