BACKGROUND: Chlorofluorocarbons (CFCs) have traditionally been used as propellants in pressurized metered-dose inhalers (pMDIs), which are often used to deliver drugs to the lungs for the treatment of reversible obstructive airways diseases. However, CFCs are harmful to the environment and need to be phased out. In response to that phase-out of environmentally harmful CFCs, the pharmaceutical industry is developing a new generation of pMDI formulations for the inhaled treatment of asthma. These formulations contain hydrofluoroalkanes (HFAs) in redesigned metered-dose inhalers. OBJECTIVES: This study primarily sought to establish clinical equivalence between a new HFA-formulated formoterol pMDI and the conventional formoterol DPI in the treatment of patients with moderate-to-severe asthma. METHODS: We enrolled 51 patients aged 18-70 years old who had stable persistent asthma. All patients were randomized to receive a single dose of each of the following 4 treatments in a double-blind, crossover manner: formoterol HFA pMDI 24 microg, formoterol HFA pMDI 12 microg, formoterol DPI 24 microg or placebo. RESULTS: Of the 51 patients randomised, 46 were evaluable for efficacy. The 12-hour average FEV1 was 2.885, 2.746, 2.916 and 2.353 liters in the HFA 24-microg, HFA 12-microg, DPI 24-microg and placebo groups, respectively. Assessment of 95% CIs revealed that the HFA pMDI 24-microg and DPI formulations were equivalent and that both were significantly superior to placebo (p < 0.001). Improvements in lung function were also significantly superior to placebo in the HFA 12-microg group, but the effect was more moderate than that observed in the higher dose groups. CONCLUSIONS: This study indicates that the formoterol HFA-formulated pMDI provides equivalent bronchodilating effect to the formoterol DPI at the 24-microg dose.