Background: Inhaled glucocorticosteroids (GCS) are the most effective longterm controller medications for the treatment of persistent asthma. Currently, however, available delivery devices limit their use in young children. A nebulized formulation of budesonide has been developed to address the needs of infants and young children. Objective: To evaluate the efficacy and safety of once-daily budesonide inhalation suspension in children 6 months to 8 years old with mild persistent asthma not on inhaled GCS. Methods: Three hundred fifty-nine children were randomized to receive once-daily budesonide inhalation suspension (0.25 mg, 0.50 mg, or 1.0 mg) or placebo via a Pari LC-Jet Plus(TM) nebulizer for 12 weeks. Efficacy assessments included nighttime/daytime asthma symptoms, pulmonary function (subset of patients), rescue medication use, and treatment discontinuations. Safety was based on adverse events and assessment of HPA-axis function. Results: Demographics, baseline characteristics, asthma symptoms, and pulmonary function were similar across treatment groups. Mean nighttime/daytime asthma symptom scores were 1.19 +/- 0.63 and 1.34 +/- 0.53, respectively. Mean duration of asthma was 36.3 months and mean FEV1 was 81.3% of predicted with 27.7% reversibility. Following 12 weeks of treatment, all budesonide inhalation suspension doses produced significant improvements in nighttime/daytime symptoms (P less than or equal to.049) and significant decreases in rescue medication use (P less than or equal to.038) compared with placebo. Significant improvements (P less than or equal to.044) in FEV1, were observed in the 0.5- and 1.0-mg budesonide inhalation suspension groups. There were no differences between doses of budesonide inhalation suspension. Adverse events and basal and ACTH-stimulated cortisol levels were similar among all groups. Conclusion: Once-daily administration of budesonide inhalation suspension was well tolerated and effective for the treatment of mild persistent asthma in infants and young children not adequately controlled with bronchodilators or non-GCS antiinflammatory treatments.