Nebulization of beta-agonists is preferred as a mode of treatment in moderate to severe asthma. Few studies, however, have compared its use in this population using an ultrasonic versus a jet nebulizer. The purpose of the study was to compare bronchodilator responses to albuterol between an ultrasonic and a jet nebulizer in moderate to severe asthma. Fifteen stable, moderately to severely asthmatic patients were randomized to receive the ultrasonic or jet nebulizer for 2 weeks. They were then crossed over for an additional 2 weeks. Albuterol was the agent used. The bronchodilator response was measured at baseline, and up to four hours after treatment with each nebulizer. Daily peak flows were then done for 2 weeks. The maximal percentage of increase in FEV 1 at 30 minutes using the ultrasonic nebulizer was 39.9 ± 8% (P < .001) versus 25.1 ± 7.6% (P = .005) using the jet nebulizer. There were no other differences between the ultrasonic and the jet nebulizer in FEV 1 or FVC during the 4-hour spirometry. During the home trial, the difference in evening PEFR between the jet nebulizer (69.05 ± 14.9 L/min) and the ultrasonic nebulizer (90.11 ± 18.7 L/min) was significant (P = .04). In summary, the ultrasonic and jet nebulizers produced comparable bronchodilator responses to albuterol in stable, moderately to severely asthmatic patients.