Multiple studies have examined adding nebulized ipratropium bromide to intermittent albuterol for the treatment of acute asthma. Although continuous nebulized treatments in themselves offer benefits; few data exist regarding the efficacy of adding ipratropium bromide to a continuous nebulized system. To compare continuous nebulized albuterol alone (A) vs. albuterol and ipratropium bromide (AI) in adult Emergency Department (ED) patients with acute asthma, a prospective, randomized, double-blind, controlled clinical trial was conducted on a convenience sample of patients (IRB approved). The setting was an urban ED. Consenting patients > 18 years of age with peak expiratory flow rates (PEFR) < 70% predicted, between October 15 and December 28, 1999, were randomized to albuterol (7.5 mg/h) + ipratropium bromide (1.0 mg/h), or albuterol alone via continuous nebulization using the Hope Nebulizer (B&B Technologies Inc., Orangevale, CA) for 2 h. Main outcome measures were changed in mean improvement at 60 and 120 min PEFR compared to baseline (time 0). Secondary measures were admission rates. Data were analyzed using appropriate parametric and non-parametric tests (p < 0.05 statistically significant). Sixty-two patients (30 women) completed enrollment: 32 in (AI) and (30) in (A). Four (A) and 2 (AI) patients are without 120 min data: 3 (A) and 1 (AI) were discharged after 60 min, whereas one each (A) and (AI) worsened and were admitted before 120 min. There were no statistically significant differences between treatment groups in age, sex, predicted or initial PEFR. Thirteen (19.4%) patients were admitted. There was no statistically significant difference in improvement of mean PEFR at 60 min or 120 min compared to baseline, between groups, using repeated measures analysis of variance. Mean improvement in PEFR at 60 min compared to baseline (time 0): (A) = 93.2 L/min (95% confidence interval [CI] 64.5-121.8), (AI) = 86.6 L/min (95% CI 58.9-114.3); mean improvement in PEFR at 120 min compared to baseline (time 0) (A) = 116.5 L/min (95% CI 84.5-148.5), (AI) = 126.4 L/min (95% CI 95.4-157.4). There was no statistically significant difference in admission rates between groups: 5/30 (A) and 8/32 (AI) (p = 0.62). There were no significant differences in mean improvement of PEFR at either 60 or 120 min between ED patients with acute asthma receiving continuous albuterol alone vs. those receiving albuterol in combination with ipratropium bromide.