The objective of this study was to evaluate the efficacy and safety of low doses (50 and 100 mu g b.i.d.) of hydrofluoroalkane-134a (HFA) beclomethasone dipropionate (BDP) extrafine aerosol in improving asthma control. Reformulation of BDP in a new chlorofluorocarbon (CFC)-free propellant (HFA) has produced an extrafine aerosol with increased delivery of the drug to the airways of the lung. The study population comprised 270 steroid-naive patients with mild to moderate asthma (mean baseline forced expiratory volume in 1 sec [FEV1] as a percentage of predicted normal of 65%-85%). This was a 6-week, blinded, placebo-controlled, multicenter study. Patients were randomized to receive 50 or 100 mu g b.i.d. HFA-BDP or HFA-placebo. Treatment with either 50 or 100 mu g b.i.d. HFA-BDP resulted in a significantly greater improvement compared with placebo in FEV1 (mean change from baseline as percentage of predicted normal of 6.7%, 8.6%, and 0.4%, respectively; p less than or equal to 0.01 active treatment groups vs. placebo), with a significant trend toward increasing improvement with increasing doses (p less than or equal to 0.0001). Treatment also resulted in significantly greater mean changes from baseline in morning peak expiratory flow compared with placebo (29.5, 33.8, and 5.0 L/min, respectively; p less than or equal to 0.01 active treatment groups vs. placebo). All other pulmonary function and asthma symptom measures supported these data. The study treatments were well tolerated. These results show that low doses of HFA-BDP extrafine aerosol effectively improve asthma control in adult patients with mild to moderate asthma. However, it is important that inhaled corticosteroid therapy is still given at a dose high enough to control airway inflammation as well as asthma symptoms.