PURPOSE OF REVIEW:Recent application of advanced culture-independent molecular techniques for the identification of microorganisms has contributed to our knowledge on the role of early-life microbial exposure and colonization in health and disease. The purpose of this review is to present the current perspectives regarding the role of microbial exposure and airway bacterial colonization on the development and the activity of asthma. RECENT FINDINGS: Recent findings continue to support the protective role of early-life diverse microbial exposure against the development of atopic diseases. However, airway bacterial colonization early in life serves as a risk factor for the development of asthma. Culture-independent molecular techniques for the identification of microorganisms have challenged the traditional paradigm that the lower airway is a sterile compartment. Asthmatics, compared with nonasthmatics, appear to have a different lung microbiome composition and some of these differences might contribute to asthma activity, severity, and corticosteroid response. SUMMARY: Bacterial presence in the airway appears to influence the inception and may affect the activity of asthma. Complex interactions between different types and routes of bacterial exposures, the airway, and the immune system early in life may determine whether these exposures augment or reduce the risk of asthma development.