Infections such as lower respiratory illness potentially contribute to the initiation of asthma and are major factors in recurring acute exacerbations of the condition. Although typical bacterial respiratory pathogens such as Streptococcus pyogenes, Streptococcus pneumoniae and Hemophilus influenzae do not initiate asthmatic exacerbations, data from a subgroup of adults suggest a potential role for Mycoplasma pneumoniae and Chlamydia pneumoniae in the onset of asthma. Common cold viruses, predominantly respiratory syncytial virus (RSV) in young children and rhinoviruses in older children and adults, are the major causes of acute exacerbations of asthma. These exacerbations are not prevented with maintenance therapies that are used for chronic asthma, but do respond to short courses of systemic corticosteroids. There are continued attempts to produce a successful vaccine and antiviral agents for the treatment of RSV that are more effective and more practical to use than ribavirin, which is currently the only available antiviral for RSV. The prevention and treatment of rhinovirus infections have focused on the major receptor for the virus, intercellular adhesion molecule-1 (ICAM-1), which is located on respiratory epithelial cells. A multivalent, recombinant, antibody fusion protein identified as CFY196 has high avidity for ICAM-1 and has the potential to protect against rhinovirus infection. Another approach for preventing and treating rhinovirus infection uses a recombinant, soluble, truncated form of ICAM-1 in which the transmembrane and intracellular domains of the protein have been deleted. An initial clinical study on this agent demonstrated clinical efficacy in ameliorating the symptoms of experimental rhinovirus infection in volunteers, but did not significantly prevent infection.