The bronchodilator response after three different modes of inhalation of 0.2 mg fenoterol from a fenoterol powder inhaler was assessed in ten asthmatic children in a double-blind, placebo-controlled, cross-over study. There was a small, but statistically significant increase in response when the children inhaled as fast as possible, compared with very slow inhalations (16-19 l/min), but a breath-holding pause of 10 s after the inhalation had no significant effect on bronchodilation. Peak inspiratory flow through the inhaler, measured in 150 normal children aged 3.5-15 years, showed that all the children studied were able to generate a sufficient inspiratory flow to benefit from treatment with this inhaler. It is concluded that children using a fenoterol powder inhaler should be taught to inhale as fast as possible. They need not hold their breath after the inhalation.