||BACKGROUND: We hypothesized that asthma is preceded by a stage of recurrent episodes of wheezing during the first years of life and that inhaled corticosteroid therapy during symptomatic episodes in this early phase may delay progression to persistent wheezing. METHODS: We assigned one-month-old infants to treatment with two-week courses of inhaled budesonide (400 mug per day) or placebo, initiated after a three-day episode of wheezing, in this single-center, randomized, double-blind, prospective study of three years' duration. The primary outcome was the number of symptom-free days; key secondary outcomes were the time to discontinuation due to persistent wheezing and safety, as evaluated by height and bone mineral density at the end of the study. RESULTS: We enrolled 411 infants and randomly assigned 294 to receive budesonide at a first episode of wheezing. The proportion of symptom-free days was 83 percent in the budesonide group and 82 percent in the placebo group (absolute difference, 1 percent; 95 percent confidence interval, -4.8 to 6.9 percent). Twenty-four percent of children in the budesonide group had persistent wheezing, as compared with 21 percent in the placebo group (hazard ratio, 1.22; 95 percent confidence interval, 0.71 to 2.13)--a finding that was unaffected by the presence or absence of atopic dermatitis. The mean duration of the acute episodes was 10 days in both groups and was independent of respiratory viral status. Height and bone mineral density were not affected by treatment. CONCLUSIONS: Intermittent inhaled corticosteroid therapy had no effect on the progression from episodic to persistent wheezing and no short-term benefit during episodes of wheezing in the first three years of life. (ClinicalTrials.gov number, NCT00234390.).