Aim: To determine whether the addition of nebulised ipratropium to the therapy of acute asthma leads to a cost-effective reduction in the mean duration of admission and time to maximum peak expiratory flow rate (PEFR). Method: Patients with an admission diagnosis of acute asthma were studied in a double-blind, placebo-controlled trial in which they received a standard therapeutic regimen of continuous intravenous aminophylline, 4-hourly fenoterol nebulisation, intravenous methylprednisolone 125mg 12-hourly, and, every four hours, either nebulised saline placebo or ipratropium bromide 500mcg in 3ml saline. Data on age, gender, initial and maximum PEFR, time to maximum PEFR, and duration of hospital stay was collected from the hospital record after discharge. Statistical techniques: 2-way contingency tables for categorical variables, 1-way ANOVA for treatment effects, and life-table analysis of the time till discharge. Results: Records of 279 of the 400 patients entered in the study were suitable for analysis after excluding re-admissions, non-asthmatics and incomplete records. Baseline comparisons of age and severity on presentation showed no significant differences. The trial group did not differ significantly from the control group with respect to either time to PEFR (respectively 21.11 hours (SD 14.3) versus 22.89 (SD 15.82)) or duration of admission (5.02 (SD 3.65) versus 5.38 (SD 3.13) 6-hour units). In a sub-group of patients (n=155) demonstrating more than 100% improvement in PEFR, the time to maximum PEFR was significantly shorter in the ipratropium group (20.35 hours SD 12.4) versus 25.20 hours (SD 17.0); p= 0.045). Conclusion: The addition of ipratropium bromide to a standard treatment regimen for acute asthma reduced the time to achieve maximum PEFR in a sub-group of patients with markedly reversible airflow limitation. Overall, however, the addition did not prove cost-effective.