Previous results have demonstrated addition of long-acting beta2-adrenergic agonists to be beneficial in asthma patients already receiving inhaled corticosteroid. The purpose of this study was to determine, qualitatively as well as quantitatively, the steroid-sparing properties of salmeterol in stable asthma patients receiving maintenance inhaled corticosteroids (800-1600 microg day(-1)). In these patients, the daily dose of beclomethasone dipropionate was reduced by 200 microg each week until asthma deteriorated, with the minimal acceptable dose (MAD) being defined as the dose one step above deterioration (sensitivity period). Following this, patients received three times the MAD for 2 weeks. Patients were randomized to receive either salmeterol 50 microg twice daily or placebo and the MAD was again determined (treatment period). Forced expiratory volume in 1 sec (FEV1) was measured each week. Morning and evening peak expiratory flow (PEF), symptom score and use of bronchodilator were recorded each day. Fifteen patients received salmeterol and 19 placebo. The MAD was significantly lower in the salmeterol group compared with placebo during the treatment period (P<0.01). A 50% reduction of the MAD was achieved by more patients treated with salmeterol than placebo (P = 0.001). Salmeterol caused a significantly greater reduction in daytime symptom score and use of as-needed beta2-agoinist therapy between sensitivity and treatment periods compared with placebo (P<0.05 for both). The results demonstrate, that the addition of salmeterol to corticosteroid treatment offers a clinically relevant potential for reduction of inhaled corticosteroid dose in steroid sensitive asthmatics.