Anti-IgE (omalizumab) has been shown to be an effective add-on therapy for patients with allergic severe asthma. In this observational study patients aged over 18 year with uncontrolled severe persistent asthma are selected for add-on therapy with omalizumab. Patients were on high dose of ICS and had a documented history of 2-6 exacerbations requiring treatment with systemic corticosteroids ( with \>15 mg/day prednisone or other medications at similar dose, for at least 3 days). The individual dose and frequency of omalizumab administration is assessed from the dosing table. Lung function tests and asthma questionnaires (ACQ, AQLQ and RQLQ) are used in the aim of assessing clinical improvement after omalizumab treatment. Induced sputum (IS) and exhaled breath condensate (EBC) are used as a simple non-invasive methods for monitoring cellular and biochemical changes in the airways. Total blood eosinophil count, IS cytology, IS and EBC periostin and IL-6 concentrations are measured. Analyses are performed at entry and after 16, 52 and 104,156 weeks of omalizumab treatment.