In the early reversibility test, spirometry is repeated to assess the bron-chodilatation following the administration of an aerosol bronchodilator. It is unique spirometric test for the differential diagnosis between asthma and chronic obstructive pulmonary disease (COPD). Forced vital capacity (FVC) and forced expiratory volume in 1st second (FEV1) before and 20 minutes after inhalation of 200 microgram salbutamol were retrospectively analyzed in patients of asthma (n=65) and COPD (n=71). FVC-related parameters had no a significant effects in the differential diagnosis. No significant correlations were observed between the increase in FEV1 and age or smoking history. The best parameter in the differential diagnosis of asthma and COPD was the percentage of the increase in FEV1 / predicted FEV1, and with a cut-off level for 6.5 %, the sensitivity and the specificity were only 81 %, and 86 %, respectively. In conclusions, acute bronchodilator response has a limited value in differentiating bronchial asthma from COPD.