The relatively new chlorofluorocarbon-free solution preparation of beclomethasone dipropionate in hydrofluoroalkane (HFA-BDP) (Qvar, 3M Pharmaceuticals) generates an extra fine aerosol with a smaller particle size (mean mass aerodynamic diameter of 1.1 microm), drug deposition in the lung is more uniformly distributed, thus improving efficacy even at a low dose. This might be also important for the use of a new fixed combination containing HFA-BDP plus formoterol in one inhaler for basic therapy and for an as-need application. Further, inhalation once a day might considerably enhance patients' adherence to maintenance therapy. The aim of this study was to test clinical efficacy and safety of twice daily inhalation (b.i.d.) vs. once daily inhalation (o.d.). In a double-blind, randomised, multicenter, parallel-group study, the efficacy and safety of 200 microg HFA-BDP o.d. (evenings) was compared with 100 microg HFA-BDP b.i.d., and with placebo. The trial included 201 patients with mild to moderately severe asthma. FEV1 was the primary endpoint and treatment duration was eight weeks. The improvement of FEV1 (20.4% o.d. vs. 12.9% b.i.d. vs. 7.9% placebo) was comparable in the two BDP groups. Both were more effective than placebo (P=0.014). The efficacy of o.d. dose was also equivalent to b.i.d. dose in secondary endpoints (peak flow, beta2-sympathomimetic drug use, asthma symptom score, and nocturnal awakenings). The treatment was well tolerated. A single evening dose (200 microg HFA-BDP) is as equivalently effective as the twice daily inhalation (2x100 microg HFA-BDP) in mild to moderate asthma.