BACKGROUND This double-blind, randomized, parallel-group, placebo-controlled study investigated the efficacy and tolerability of fluticasone propionate aerosol (25, 50, or 100 mg bid for 12 weeks) administered as primary maintenance therapy to patients whose mild to moderate asthma was inadequately controlled by as-needed use of an inhaled beta-agonist. RESULTS At all clinic visits, fluticasone propionate compared with placebo was associated with significant (P<.05) improvement in pulmonary function indexed by forced expiratory volume in 1 second (FEV1) as well as fewer night awakenings and less use of rescue albuterol. Values for patient-measured morning peak expiratory flow rates (PEFR) were significantly (P<.05) higher and the use of rescue albuterol was significantly (P<.05) lower beginning 3 to 5 days after initiation of therapy in the groups treated with fluticasone propionate, compared with the placebo group. Maximal improvement in FEV1 was achieved during the second week of treatment and maintained throughout the course of therapy. Differences among the three fluticasone propionate dosing groups for these efficacy measures were not statistically significant. The incidence of adverse events was similar across groups. CONCLUSIONS These data indicate that fluticasone propionate aerosol is an effective and well-tolerated treatment for asthma and significantly improves pulmonary function within days of initiation of treatment in patients whose asthma is inadequately controlled with as-needed beta-agonists.