The aim of this study was to investigate formoterol, an inhaled long-acting beta2-agonist, in patients with chronic obstructive pulmonary disease (COPD). Six-hundred and ninety-two COPD patients, mean baseline forced expiratory volume in one second (FEV1) 54%, FEV1/forced vital capacity 75% of predicted, reversibility 6.4% pred, were treated with formoterol (4.5, 9 or 18 microg b.i.d.) or placebo via Turbuhaler for 12 weeks. Symptoms were recorded daily. Spirometry and the incremental shuttle walking test (SWT) were performed at clinic visits. Compared with placebo, 18 microg b.i.d. formoterol reduced the mean total symptom score by 13% and increased the percentage of nights without awakenings by 15%. Formoterol (9 and 18 microg b.i.d.) significantly reduced symptom scores for breathlessness (-7% and -9%, respectively) and chest tightness (-11% and -8%, respectively), reduced the need for rescue medication (-25% and -18%, respectively), and increased symptom-free days (71% and 86%, respectively). FEV1 improved significantly after all three doses of formoterol (versus placebo). No differences were found between groups in SWT walking distance. No unexpected adverse events were seen. In conclusion, 9 and 18 microg b.i.d. formoterol reduced symptoms and increased the number of symptom-free days in a dose-dependent manner in chronic obstructive pulmonary disease patients. Formoterol improved lung function at a dose of 4.5 microg b.i.d. and higher.