Respiratory infections are one of the major causes of asthma exacerbations. Among numerous pathogens that may lead to exacerbations, particular attention should be paid to atypical bacteria: Chlamydia pneumoniae and Mycoplasma pneumoniae. Despite significant frequency, infections caused by these species are underestimated due to untypical clinical course and lack of easily accessible diagnostic tests. Although acute infection can be easily linked with deterioration of asthma control, the role of respiratory colonisation by Chlamydia pneumoniae or Mycoplasma pneumoniae has not been precisely defined. It is known that serologic signs of both past infection and chronic current infection (IgA) with Chlamydia pneumoniae or Mycoplasma pneumoniae are found more often in asthmatics compared to healthy controls. Besides respiratory colonisation by Chlamydia pneumoniae or Mycoplasma pneumoniae confirmed by culture or molecular tests is also more common in asthmatics. This is particularly relevant in cases of uncontrolled asthma that followed symptoms of respiratory infection. This may lead to the conclusion that atypical infections can play a role in asthma induction in previously healthy individuals as well as deteriorations in the course of the disease. Studies mentioned above have led to the new therapeutic possibility - eradication of Chlamydia pneumoniae. In some of the studies on eradication with macrolides promising results have been gained in terms of asthma control, but in most of the cases improvement was only temporary.