This study evaluated the safety and efficacy of arformoterol and formoterol over 6-months in subjects with COPD. In a multi-center, 6-month randomized, double-blind, double-dummy trial, subjects with COPD (mean FEV(1) 1.21 L, approximately 41.0% predicted) were randomized to receive either nebulized arformoterol (15 microg BID [n = 149][ARF 15], 25 microg BID [n = 147][ARF 25]), or racemic formoterol (12 microg BID [n = 147][FORM]) delivered by DPI. The proportion of subjects with any post-treatment adverse event for ARF 15, ARF 25 microg, and FORM was 67.8%, 76.2% and 66.7%, respectively, and those with at least one COPD exacerbation was 32.2%, 30.6%, and 22.4%, respectively. Pulmonary function improved for all treatment groups and was maintained throughout the study. Mean change from baseline at 6-months for ARF 15, ARF 25 and FORM in peak FEV(1) was 0.30L, and 0.34L, and 0.26L, respectively, in 24-hour trough FEV(1) was, 0.10L, 0.14L, and 0.09L, and in inspiratory capacity was, 0.20L, 0.37L, and 0.23L. Dyspnea, (mean Transition Dypsnea Index (TDI) focal score) improved in all treatment arms (ARF 15: 1.4, ARF 25: 1.5, and FORM: 1.4) at 6 months, as did rescue short-acting beta(2)-agonists use (mean range: -1.1 to -1.3 actuations/day) and ipratropium bromide (mean range: -0.3 to -0.8 actuations/day). Health status, measured by St George's Respiratory Questionnaire, improved from baseline at 6-months in all treatment groups (mean change: -3.7 to -6.8). In this 6-month study, arformoterol and formoterol were well-tolerated, and their use was associated with improvement in pulmonary function and health status in subjects with COPD with no apparent development of tolerance.