Introduction. - Omalizumab is used as a treatment for severe allergic asthma. Its intended mechanism of action is based on its anti-IgE proprieties. However, recent studies have highlighted other mechanisms of action. State of the art. - Omalizumab treatment is associated with a decrease in the number of dendritic cells, T and B lymphocytes and eosinophils. This anti-inflammatory activity is characterized by a decrease in the levels of several cytokines involved in the recruitment, activation and survival of eosinophils and mastocytes, and in a Th2 orientation of the immune response. A modulation of bronchial remodeling by omalizumab has recently been shown. A decrease in the production of extracellular matrix components and in the proliferation of smooth muscle cells could be involved in this modulation. These mechanisms of action could explain in part the clinical efficiency of omalizumab in non-allergic conditions such as non-allergic asthma, non-allergic urticaria or nasal polyposis. Conclusion. - A precise knowledge of the mechanisms of action of omalizumab could allow the identification of biomarkers predictive of efficacy of this treatment. These could be useful tools in the phenotyping of severe asthma. (C) 2016 SPLF. Published by Elsevier Masson SAS. All rights reserved.