Continuous nebulization is a safe and practical method of administration of beta 2 -adrenergic agonists during acute asthma. There are essentially 2 types of continuous nebulizer systems; 1 utilizes a large volume nebulizer and the other a small volume nebulizer attached to a constant volume infusion pump. We compared the volume output characteristics of these 2 systems. Study performed at Danbury Hospital. Both types of continuous nebulizers were reconstructed as reported in the literature and output monitored hourly for 4 hours. A total of 9 nebulizers from each type of continuous nebulizer was evaluated, 3 from each of 3 different lots. The volume output of the large volume nebulizer ranged from 37.7 to 55.4 mL/h with a mean of 45.96 mL/h (P= .0001). Contrasts within the repeated measure ANOVA revealed that all pairwise contrasts in time were significant (P < .05) except for the 60 and 120 minute means. The volume output of the small volume nebulizer ranged from 15.0 to 16.6 mL/h with a mean of 15.88 mL/h. There was a significant difference in the mean volume output across time for the 60-minute value only. No other significant differences were found. These data suggest that the small volume nebulizer utilized in this manner for continuous nebulization is a more consistent delivery device than the large volume nebulizer. Further data are required on both actual drug output and mass median aerodynamic diameter of the particles generated by these nebulizers before one can recommend a particular system.