Traditionally, patients with acute airflow obstruction are treated with bronchodilator aerosols delivered by continuous flow nebulizers. While bronchodilator administration with the metered dose inhaler (MDI) and reservoir or spacer attachment is as effective as administration with the nebulizer in most settings, the former has not been widely accepted for treatment of acute airway obstruction in the emergency room. We compared the efficacy of the continuous flow nebulizer to that of the MDI with InspirEase (reservoir spacer) in 75 patients (45 men and 30 women), ages 18-73 (chi 44 years) who presented to the emergency room with acute asthma and COPD. Subjects in each group (22 COPD and 53 asthma) were randomly assigned to treatment with three puffs of metaproterenol (0.65 mg/puff) via the MDI with InspirEase plus nebulizer with placebo, or placebo MDI with InspirEase plus nebulizer with 15 mg metaproterenol in double blind fashion. Either treatment was given three times at 30 min intervals. The FEV1 and dyspnea scores according to the Borg scale were measured at baseline, 30 min after the first treatment, and 30 min after the third. There was no significant outcome difference between the two treatments in either diagnostic group. There also was no significant outcome difference for patients with baseline FEV1 less than 0.9L. Serum theophylline levels, the need for concomitant therapy with corticosteroids, or additional emergency room therapy after the study, hospitalizations and treatment side effects did not differ between treatment groups. We conclude that there is no demonstrable advantage of a continuous flow nebulizer over an MDI with InspirEase for the treatment of acute airflow obstruction.