Summary: The paper discusses the importance of biological therapy which affects the IL-5 signaling pathway in severe eosinophilic asthma. Asthma phenotype with eosinophilia is very well known although not fully understood or precisely defined. Eosinophilia in the blood and sputum is associated with a more severe course and worse disease control. Interleukin-5 (IL-5) is the main cytokine involved in the activation of eosinophils, which cause airway inflammation. Th2 cytokines (IL-13, IL-5) are associated with allergic sensitization but these cytokines can also be produced by innate lymphoid cells contributing to airway eosinophilia. Monoclonal antibodies targeting IL-5 (mepolizumab, reslizumab) and its receptor IL-5R (benralizumab) and clinical test results are described in the paper. Recent studies have shown that they reduce asthma exacerbations, have a glucocorticoid-sparing effect and improve health-related quality of life and lung function. Precise assessment of severe asthma is crucial for monitoring the treatment.