The efficacy of terbutaline inhaled from different aerosol systems was studied in 13 adult asthmatics. Terbutaline 1 mg was delivered from a pressurised aerosol, 1 and 4 mg were inhaled from a nebuliser, 1 mg was inhaled through a pressurised aerosol with a pear-shaped, 750 ml spacer, and 1 mg was inhaled from a nebuliser with Intermittent Positive Pressure Ventilation (I.P.P.V.). An open, randomized, cross-over design was used. The bronchodilator effect was evaluated by recording hourly flow-volume curves and the FEV1.0 for 5 h after treatment. No significant difference in bronchodilatation was observed after inhalation of 1 mg terbutaline from different aerosol systems, except following use of the nebuliser, which required approximately four times as much terbutaline to obtain the same effect as the ordinary spray.