Despite of the tremendous progress, which was made within the last few years in the diagnostics and treatment of asthmatic patients, there is a lack in a simple, non-invasive methods, which could be useful in the diagnostics and anti-inflammatory treatment monitoring. Invasive methods, such as bronchofiberoscopy (bronchoalveolar lavage fluid analysis and bronchial biopsy), enabled the better understanding of the pathophysiology of asthma and the elaboration of the grounds of pharmacological treatment of this disease. Unfortunately, these methods are less useful in the clinical practice due to their invasiveness. Spirometry, which is essential in diagnostics and treatment of asthmatics, is only indirect way of the airway inflammation assessment. Recent studies are focused on noninvasive methods of the evaluation of airway inflammation, such as measurements of exhaled nitric oxide (FENO) and allergic inflammation mediators in the inducible sputum. The higher degree of inducible form of nitric oxide synthase (iNOS) expression and higher levels of nitric oxide in exhaled air are observed in asthmatic patients. Many studies confirm, that the measurement of exhaled nitric oxide is a simple, non-invasive method in diagnostics and treatment monitoring in asthmatics, which does not intensify the symptoms of asthma.