Exhaled NO is a marker of airway inflammation. Its level is increased in several conditions of chronic airway inflammation. It correlates well with sputum eosinophilia and bronchial hyper-reactivity in none steroid treated subjects. It is useful as an adjunct in asthma diagnosis, monitoring asthma control, adherence to ICS, and in predicting asthma exacerbations. Its usefulness in the assessment of the severity of asthma exacerbations and response to treatment in the emergency room has not been determined yet. Few studies have shown that the measurement of Fractional Exhaled Nitric Oxide (FeNO) in the emergency room did not correlate with asthma severity or predict treatment outcomes. It also did not correlate with other measurements like symptom score or PEFR (peak expiratory flow rate). However, those studies were not in the same setting as we are proposing here. In other words, they were using standard medications only. Nevertheless, this issue needs to be studied further, especially with the evidence that ligand binding of the cytoplasmic GR leads to rapid activation of the NO synthase in endothelial cells and thereby may alter the level of FeNO. This study is a good opportunity to examine the value of measuring FeNO in the emergency especially that its measurement is easy, reliable and reproducible. The availability of new portable, valid, and reliable devices to measure FeNO (NIOX Mino) makes it even more attractive.