In summary, bacterial organisms are clinically relevant contributors to asthma exacerbations, and have received much less attention than viruses in this process. Streptococcus pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis have been linked to asthma exacerbations, particularly when sinusitis is present. Treatment therefore should be directed toward these organisms if a bacterial cause is suspected. The atypical bacteria--specifically, C. pneumoniae and M. pneumoniae--deserve special attention. Data suggest a link between these organisms and the exacerbation of asthma, as well as suggest that these organisms may be causative in asthma development. The existing data are not conclusive, but are suggestive enough to drive studies evaluating them as a possible mechanism in asthma pathogenesis. An animal model evaluating M. pneumoniae and C. pneumoniae would be ideal, but at present no model exists in which chronic infection with these organisms results in bronchial hyperresponsiveness. There is active work in this area, however. Alternative investigations include continued evaluation of these organisms by several modalities, including culture, serology, and PCR, along with evaluation of the host response. Many questions remain, but the ground is fertile for continued investigation.