Evaluation of patients with chronic obstructive pulmonary disease (COPD) often includes the use of post-bronchodilator reversibility testing to guide treatment decisions. Recommendations for reversibility testing differ and there is no universally accepted method or outcome criterion. A survey of recent clinical trials with beta2-agonists in COPD illustrates the diversity of methods used to assess reversibility and highlights the difficulty of comparing data from such trials. Two recent studies demonstrated the benefits of treatment with the long-acting beta2-agonist bronchodilator formoterol (Foradil Aerolizer) in patients with COPD. When patients were classified according to their degree of reversibility as partially or poorly reversible, improvements were observed in both groups irrespective of the definition applied. These results suggest that bronchodilator reversibility testing should not be used as a rigid basis for treatment decisions with beta2-agonists in COPD patients. There is a pressing need for the role of reversibility testing to be clearly defined.