In many countries the majority of patients with asthma are now treated with inhaled beta 2-agonists as required and regular inhaled steroids. Compliance with asthma medication is poor, particularly for inhaled steroids, which do not give immediate relief of symptoms. An inhaler combining a beta 2-agonist and a steroid may improve compliance and give better control of asthma. We have studied the effect of a fixed combination dry powder inhaler (Turbuhaler) containing terbutaline (250 micrograms) with budesonide (200 micrograms) compared with each drug given alone in a double-blind, crossover study in 74 patients with mild to moderate asthma. This was a multicenter study performed in general practice. After a 1-wk run-in period with placebo inhaler, each treatment was given twice daily for 4 wk in randomized order. Patients measured symptom scores and rescue inhaled beta 2-agonist use and recorded peak expiratory flow (PEF) twice daily. In nine patients recruited to a hospital center, airway responsiveness was measured by the concentration of methacholine required to produce a fall in FEV1 of 20% (PC20) at the end of each treatment period. Of 74 patients randomized, 68 completed all three treatment periods. Their mean age was 37 (18-60) yr and PEF 80 (43-116) % predicted. Combination treatment gave a significant improvement in morning and evening PEF budesonide or terbutaline treatment periods (p < 0.01), and a significant reduction in asthma symptom scores and rescue beta 2-agonist use (p < 0.05). There was a significant patient preference for the combination inhaler.(ABSTRACT TRUNCATED AT 250 WORDS)