Objective To compare the clinical effectiveness and patient acceptance of a large spacer device (Nebuhaler™) for delivery of metered dose aerosol (MDI) terbutaline with nebulised wet aerosol terbutaline. Design Randomised open crossover study over two sequential four week treatment periods, following a two week run‐in. Setting Multi‐centre including five adult thoracic units and three paediatric centres throughout Australia. Patients Thirty‐eight adults and 23 children with clinical asthma and reversible airflow obstruction (increase in forced expiratory volume in one second [FEV1] of ≥15% in response to inhaled bronchodilator) entered the study proper. Six adults and one child withdrew. Interventions Terbutaline was administered four times dialy via Nebuhaler/MDI or nebuliser. Clinical assessment with spirometry and peak flow readings was made after run‐in and at the end of each treatment period. Patients recorded on diary cards daily peak expiratory flow rates and symptom scores and comparisons of these results for each treatment period were made. At the completion of the study patients answered a treatment preference questionnaire. Results No differences were found between the two treatment periods in diary card peak flow recordings and symptom score data, and in clinical assessment of spirometry and peak expiratory flow rates. There were also no differences between spirometry and peak flow values recorded at the clinic at randomisation and at the end of each treatment period, suggesting stable basal airflow obstruction over the period of the study. Thirty‐two per cent of adults and 52% of children preferred the Nebuhaler/MDI combination, mainly because of convenience of use. Treatment preference was not related to any measured index of lung function. Conclusions MDI terbutaline delivered via Nebuhaler provides clinical benefit similar to that of wet aerosol terbutaline in the long‐term domiciliary management of patients with stable airflow obstruction.