 This study will compare a single dose of oral dexamethasone to placebo in a multicenter, randomized, double blind trial of infants aged 2 to 12 months with first-time bronchiolitis defined as wheezing within 7 days of onset. This is given as additional therapy beyond any other routine therapy used at that center. No current standard therapy is withheld, and no additional tests or other treatments are part of the study.The primary hypothesis is that dexamethasone will be more effective than placebo in preventing hospital admission. The secondary hypotheses are that dexamethasone will decrease respiratory scores and possibly the duration of the disease when compared to placebo, and that dexamethasone will be as safe and as well tolerated as placebo. 