The association between respiratory infections and asthma exacerbations was first observed in the early '70s. In particular, the role of viral upper respiratory tract infections has been evaluated both in pediatric and adult populations. More recently, evidence of Mycoplasma and Chlamydia pneumoniae involvement in asthma attacks has been reported. These pathogens are also involved in chronic asthma, and both in vitro and animal model studies indicate that atypical agents may play a role in the pathogenesis of the disease. Further research is required to determine whether specific antibiotic treatment may alter the natural history of asthma.