Wheezing is a symptom, not a diagnosis. Wheezing disorders are not equal to childhood asthma. Wheezing in the youngest children is often episodic, associated with upper respiratory infection. Early wheezing disorders, particularly in the first 2-3 years of life, should be considered as largely independent of later childhood asthma. It is difficult to distinguish an initial episode of asthma triggered by a viral respiratory infection from acute viral bronchiolitis. Most of the infants with wheezing have transient conditions associated with diminished airway function at birth and do not have increased risks of asthma or allergies later in life. There is no evidence for an overall beneficial clinical effect of nebulized a2-agonists in acute severe wheezing episodes or acute bronchiolitis in infants, although some may seem to respond.