In a double-blind, cross-over study, 21 children with acute severe asthma were treated with terbutaline (0.10 mg/kg) delivered by a pressurized aerosol with a 750 ml spacer (Nebuhaler) or as a nebulized solution by a Pari Inhalier Boy. A significant increase in FEV-1 was seen after both treatments. Furthermore, nebuhaler treatment resulted in significantly greater bronchodilation than treatment with the nebulizer (p less than 0.05). Irritation of mouth and throat and coughing were observed in 12 patients during nebuhaler treatment. These problems were not seen when the nebulizer was used. Eleven children preferred treatment with the nebuhaler, whereas only one child preferred the nebulizer. The main reason for preferring the nebuhaler was the shorter administration time.