Bronchial responsiveness to bronchodilator medications is usually tested to establish reversibility of airflow obstruction. Among the various tests to establish bronchodilator response, FEV1, FEF(25-75%) or FEF50%, and FVC are the most widely used. In a cross-sectional study, we assessed spirometric responses after administration of bronchodilator in 187 workers with obstructive pattern in spirometry. Considering responsiveness to bronchodilator (200 cc and 12% increase in FEV1 or FVC), the study cases were divided into responsive or non-responsive groups, and the average increase in spirometric indices were measured and compared between two groups. 35.8% of cases were responsive to bronchodilator. Among responsive cases, FEV1 was the most frequent index increased significantly; And PEF and FVC were the least frequent ones. The highest mean increase from baseline after administration of bronchodilator was observed in FEF75%. Increases in all indices were significantly higher in responsive group. The increase in FEV1% predicted was inversely correlated with baseline FEV1. In conclusion, we consider that FEV1 is the most reliable spirometric index for assessing bronchodilator response. And Bronchial reversibility has an inverse relationship with baseline measures.