STUDY OBJECTIVE: Corticosteroids are thought to exert their physiologic effects in asthma over the course of several hours. In this study we tested the hypothesis that intravenous methylprednisolone improves airflow in a shorter time frame (2 hours) in adults with acute asthma. METHODS: In a randomized, double-blind, placebo-controlled trial, 56 adult asthmatic patients with peak expiratory flow rates (PEFRs) less than 50% predicted after an initial albuterol aerosol treatment were studied. These patients were randomly assigned to treatment with either 125 mg of intravenous methylprednisolone or an equivalent volume of normal saline solution (placebo). Patients were also treated with identical schedules of nebulized ipratropium and albuterol. Patients were recruited from an emergency department at an urban academic medical center. The primary endpoints were changes in PEFR and in percent predicted PEFR over time. PEFRs were assessed at baseline and at 1 and 2 hours. Heart rate changes over time and the proportion of admissions in the 2 groups were also compared. RESULTS: The increases in PEFR and percent predicted PEFR over time were both significantly greater in the methylprednisolone treatment group (P =. 002 and P =.005, respectively). The increases in geometric mean peak flow at 60 and 120 minutes were 79 and 96 L/min for the methylprednisolone group and 54 and 68 L/min for the placebo group. There was also a significantly different change in heart rates with time between the methylprednisolone and placebo groups (P =.029), with the placebo group showing a moderate increase in heart rate over time. Although the proportion of patients admitted for status asthmaticus was less in the methylprednisolone treatment group (8/30) compared with the placebo group (10/26), this difference in proportions (-.118, 95% confidence interval -.363 to.127) was not significant. CONCLUSION: These data suggest that use of corticosteroids should be considered relatively early in the treatment of patients with acute asthma in whom initial bronchodilator therapy fails to produce an adequate response.