To find out how many children with acute asthma responded to one or two doses of nebulised salbutamol and whether this response could be predicted 100 children were studied prospectively from two district hospitals. Twenty three children needed only one nebulised dose and 19 responded to two. Significant factors differentiating these responders from the remainder were age (24 (63%) of those aged 6 or more responded compared with only six (19%) of those aged 3 or less); regular treatment with a beta 2 sympathomimetic; and use of a rotahaler or aerosol. Those requiring more intensive treatment had faster pulse and respiratory rates on admission and one hour after the first nebulised dose. Another useful clinical sign was persistent supraclavicular indraw. Pulsus paradoxus and peak expiratory flow rate were of limited value in the younger children who had worse asthma. Of 29 children receiving intravenous treatment, 18 (62%) were aged 3 or less, whereas only two (7%) were aged 6 or over. The older children who responded initially to nebulised salbutamol could have been safely reassessed at home, which would have considerably reduced hospital admissions.