In a double blind cross-over study the bronchodilator response after eight different modes of inhalation of terbutaline from a pressurized aerosol with a tube spacer was assessed in fifteen asthmatic children. Slow inspiratory flow rates (15–30 1/min) were found to be associated with a statistically significant increase in response when compared with flow rates higher than 70 1/min (P<0.01). Tilting the head back during the inhalations and a breath-holding pause of 10 sec after the inhalation had no significant effect upon bronchodilation. In addition, bronchodilation was the same whether the children inhaled from RV or FRC. and whether they inhaled as deeply as possible or only to about half the maximum volume. The results suggest that efforts should be made to develop a new and more simple set of instructions for the use of tube spacer aerosols.