Two Nebuhaler techniques were compared by measuring the response to terbutaline 0.25 mg in 13 asthmatic children. Five breaths each sufficient to operate the Nebuhaler valve resulted in greater bronchodilatation after 10 minutes (P less than 0.05) than two deep inspirations from residual volume each held for 5 seconds. The peak responses were similar and both methods produced significant bronchodilatation compared with placebo. Either method is satisfactory in children but the former is easier to perform.