Inhaled glucocorticosteroids such as budesonide have an important role in the management of asthma. Although these agents have traditionally been given twice daily, evidence is accumulating that once-daily treatment may be as effective as twice-daily administration. The efficacy of budesonide Turbuhaler® (Astra, Lund, Sweden), 400 μg once daily in the evening or 200 μg twice daily, was compared in a randomized, double-blind study involving 181 patients (75 men, 106 women; mean age 30·8 years) with mild asthma [mean forced expiratory volume in 1 s (FEV1) 92·8% pred.] who had not previously been treated with inhaled glucocorticosteroids. After a 2-week run-in period, patients were randomized to either regimen and treated for 6 weeks. This was followed by two 8-week open treatment periods, during which all patients received budesonide Turbuhaler®, 200 μg once daily during the first period and 100 μg once daily during the second period. The mean change in morning peak expiratory flow (PEF) during the double-blind treatment period was 16·91 min−1 in patients receiving once-daily treatment and 17·21 min−1 in those receiving twice-daily treatment. Similarly, there were no significant differences in evening PEF, symptom scores, bronchodilator use or spirometry data between patients receiving once- and twice-daily treatments. The improvements in morning PEF, symptom scores and bronchodilator use seen during the double-blind treatment period were maintained during the two open treatment periods. It is concluded that once-daily treatment with budesonide Turbuhaler® is as effective as an initial therapy twice-daily treatment in patients with mild persistent asthma, and that the initial dose can be reduced to maintenance levels (including 100 μg) without loss of asthma control.