Respiratory infection, most prominently bronchiolitis, contracted in infancy is frequently associated with recurrent wheezing episodes and asthma in later life. Atopic individuals and those with a family history of allergy or asthma in first-degree relatives are especially susceptible to the development of chronic airway dysfunction and should be identified early. It is also noteworthy that parenteral cigarette smoking may serve as an additional marker of the high-risk patient. Respiratory infection affecting older children and adults is more commonly due to rhinovirus and influenza A and may cause a transient hyperreactivity to bronchoconstrictor agonists, but does not cause persistent dysfunction. The mechanism(s) by which antecedent respiratory infection is related to recurrent wheezing and asthma remain speculative, and at present a direct causal relationship cannot be established with certainty. Infectious respiratory disorders are also a cause of exacerbations of asthma in adults but more commonly in children, and these also are primarily viral in origin. Consequently, in the absence of clear evidence of bacterial infection, routine antibiotic use in this setting is unwarranted.