In the present trial we investigated the time course of inhaled salmeterol and formoterol bronchodilation in comparison with that of inhaled salbutamol and placebo in 16 patients with moderate to severe chronic obstructive pulmonary disease (COPD). The study was performed using a single-blind crossover randomized study. The bronchodilator activity of 200 micrograms salbutamol, 50 micrograms salmeterol, 24 micrograms formoterol and placebo, which were all inhaled from a metered dose inhaler, was investigated. Our results showed that salmeterol and formoterol are efficacious in reducing airflow obstruction in patients suffering from COPD. We found similar times of onset to improve FEV1 by 15% for salmeterol and formoterol (salbutamol behaving faster), while the duration of action showed the expected differences between the two long-acting drugs and salbutamol. The results indicate that long-acting beta 2-agonists appear to be very effective in improving airway limitation in patients suffering from COPD. Although the onset of bronchodilation after inhaling salmeterol and formoterol is slightly delayed compared with salbutamol, this is of little clinical importance since in these patients salmeterol and formoterol must be intended for maintenance treatment and not immediate symptomatic relief.