Patient-guided management of asthma using adjustable dosing of budesonide/formoterol in a single inhaler (Symbicort) was compared with fixed dosing in an open-label, multicentre, randomised study. Patients, uncontrolled on an inhaled corticosteroid (ICS) or controlled on an ICS and a long-acting beta2-agonist, entered a 4-week run-in period and received budesonide/formoterol (80/4.5 or 160/4.5 microg), 2 inhalations b.i.d. Following randomisation, the fixed-dosing group (n = 764) continued this regimen for a further 12 weeks. The adjustable-dosing group (n = 775) could step down to 1 inhalation b.i.d. if symptoms were controlled, and, at early signs of worsening symptoms, promptly step up to 4 inhalations b.i.d. for < or = 2 weeks. During run-in, National Heart, Lung and Blood Institute symptom-severity grading was maintained in 60% and improved in 31% of patients, clinic peak flow increased from 400 to 4191/min (P<0.001), and health-related quality of life (overall MiniAQLQ) improved from 4.6 to 5.4 (P<0.001). Patients effectively used the adjustable-dosing regimen; 79% reduced budesonide/formoterol dosage and, compared with fixed dosing, the number of inhalations were significantly lowered (3.2 vs. 3.8 inhalations/day, P<0.05). Both regimens were well tolerated. In both groups, symptom control was maintained or improved in 85-86% of patients, and 94% experienced no treatment failures. Consistent with current guidelines, adjustable maintenance dosing with budesonide/formoterol in a single inhaler provides effective asthma control at reduced medication doses.