In this article the author presents the latest data on the role of bacterial and viral respiratory tract infections in the pathogenesis of bronchial asthma. The effect of microorganisms and their products on immunological and non-immunological mechanisms of cell mediator release, cytokine activity, bronchial hyperreactivity and acute and late asthmatic reactions are discussed. As this brief review shows, the role of respiratory infections in the development of different types of asthma is very important.