The British guidelines on asthma management and other recent reviews have widely advocated the use of spacer devices for asthmatic patients.1-3 Spacer devices allow aerosol to be inhaled through a valved mouthpiece during a single inspiratory breath or as is often recommended for children during tidal breathing.2During the expiratory phase of a tidal breathing manoeuvre the valve closes. Although this action prevents leakage of aerosol from the spacer and ingress of moisture into the holding chamber, there is an inevitable increase in the expiratory resistance. We have measured the resistance …