Asthma pathogenesis seems to be a result of a complex mixture of genetic and environmental influences. There is evidence that Mycoplasma pneumoniae and Chlamydophila pneumoniae (formerly known as Chlamydia pneumoniae) play a role in promoting airway inflammation that could contribute to the onset and clinical course of asthma. Evidence also indicates that when antimicrobial therapy can eradicate or suppress these organisms, it may be possible to alter the course of the disease. Certain macrolide antibiotics have been shown to improve control of asthma symptoms and lung function in patients diagnosed with acute C. pneumoniae or M. pneumoniae infection. Positive polymerase chain reaction studies for C. pneumoniae or M. pneumoniae are needed to select asthma patients for chronic treatment. Macrolide antibiotics may also have independent anti-inflammatory activity that may be useful in the management of asthma and other inflammatory diseases.