BACKGROUND In acute severe asthma the optimal dose, frequency, duration and method of administration of beta-2 agonists is unknown. No study to date has evaluated the efficacy of high dose beta-2 agonists beyond the initial two hours. OBJECTIVE (1) To determine whether high-dose continuous nebulization of albuterol (7.5 mg/h) is as safe and as efficacious as high-dose intermittent nebulization of albuterol (2.5 mg every 20 minutes) for four hours. (2) To evaluate whether there is a continual improvement using high dose therapy beyond two hours. METHODS We devised a simple means of continuous nebulization calibrated to deliver 7.5 mg albuterol per hour. Twenty-two nonsmoking, patients with acute, severe asthma who presented to the emergency department with less than 60% predicted normal PEFR were randomized to either the continuous or intermittent group. All patients received intravenously 125 mg methyl prednisolone on initiation of the study. No theophylline was administered. Spirometry and vital signs were measured at baseline and every 30 minutes thereafter. Electrocardiograms were obtained on all patients and all patients had continuous cardiac monitoring. RESULTS Both groups doubled their baseline spirometric values over the four-hour period (P < .0001). The FEV1 did not differ significantly between regimens at any time interval. Improvement from 120 minutes to 240 minutes was statistically significant (P < .0001). There was no significant difference in vital signs at the end of the study compared with baseline in either group, nor between the two groups at any time interval. CONCLUSIONS High-dose continuous nebulization of albuterol is as safe and as efficacious as intermittent nebulization of albuterol in the early treatment of asthma in an emergency department. To our knowledge, this is the first study showing continued significant improvement beyond the initial two hours of therapy using high dose nebulized beta-2 agonists.