BACKGROUND: Spacers devices are commonly used in aerosol therapy; how- ever, they are bulky and require regular cleaning. A compact open spacer (OS, Synchroner, Fisons, UK) has been developed to overcome this problem. We com- pared bronchodilator efficacy associated with its use to efficacy of same dose via three other spacers: Volumatic (Glaxo Laboratories), Nebuhaler (Astra Labor- atories), Inspirease (Key Pharmaceuticals). MATERIALS & METHODS: Sixteen asthmatics (> 20% reversibility of FEV1) took part in the study. In random order, they used a different device on each of the 4 study days to inhale 2 puffs of a com- bination aerosol (1 mg reproterol and 2 mg sodium cromoglycate, Aarane). We recorded results of spirometry before and 5, 30, and 60 minutes after bron- chodilator inhalation. RESULTS: At each time, we found no significant difference in bronchodilation. CONCLUSION: OS is as efficient as other commonly used spacers to produce bronchodilation resulting from a conventional dose of repro- terol.