It is not known whether infants with recurrent wheezing have persistent airway narrowing when not acutely symptomatic, and whether airway function in these infants is related to ETS exposure, Fm Asthma, and male gender. When recurrently wheezy infants are asymptomatic, airway function may be low or normal, and low airway function may be fixed or reversible with a bronchodilator. It is important to determine whether these infants have functional and structural abnormalities when they are not acutely symptomatic, and to determine how lung structure relates to lung function. Only then can we design effective therapeutic interventions for recurrently symptomatic infants, as well as, design early intervention strategies.