Twenty-five patients with reversible airways obstruction inhaled salbutamol (200 micrograms) from the standard press and breathe-metered dose inhaler or a new breath-actuated metered dose inhaler (Aerolin in the Autohaler inhalation device; 3M Health Care Ltd.) in a single dose, double-blind, double-dummy, 2-period, cross-over study. Forced expiratory volume in 1 s, forced vital capacity and peak expiratory flow rate were measured in the 4-hour period after inhalation. The equivalence of the two inhaler devices was determined by analysis of the peak change and time to peak, with reference to the initial recorded baselines of the measured parameters. The efficacy of the two devices was very similar. The breath-actuated device is likely to benefit inhaler users who suffer from poor co-ordination of actuation and inhalation with a standard inhaler.