Aim of the study: The purpose was to investigate the correlations between bronchial hyperresponsiveness and nitric oxide (NO) levels measured in exhaled air and to establish their involvement in airways inflammation process in allergic patients. Material and methods: 188 subjects (mean age 28 ± 7.5; 47.1% male, 52.9% female) with chronic cough were investigated under the suspicion of bronchial asthma/allergic rhinitis. After signing the written informed consent and based on questionnaire methods (ACT for asthma, and SQUAR-E for allergic rhinitis), in accordance with the international criteria (GINA for asthma, and ARIA for allergic rhinitis, 145 subjects were included into study as allergic patients with mild and moderate asthma ± allergic rhinitis, without corticotherapy for at least 2 months. Depending on pulmonary function disorders, the bronchomotricity tests are performed, including the bronchial methacholine provocation test, in patients having FEV1 (forced expiratory volume in 1 second)≥ 60% of ideal value or distal obstructive syndrome. Methacholine solution is inhaled using Wright nebulizer, in progressively increasing doses, starting from 0.075 mg/ml to the 15 mg/ml. Bronchial hyperreactivity was assessed by PC20 value (the methacholine concentration which induces a 20% decrease of FEV1), which also indicates the severity of bronchial hyperreactivity. Nitric oxide level in the exhaled air (FENO) was measured using the computer NOXIMETER device, which determines this concentration every 2 minutes of forced respiration. Results: Asthma severity, according to GINA criteria was established in 59 allergic patients after bronchial provocation tests, as mild persistent asthma (41), moderate asthma (17), and severe asthma (1). The mean severity degree of bronchial hyperreactivity in methacholine testing, estimated by PC20 was 3.26±2.6 mg/ml. The ACT score at the biginning of the study was 14.37±2.4. NO from exhaled air was correlated (significant correlation index r = 0.51) with the degree of bronchial hyperreactivity, and FENO was determined between 5 and 173 ppb. Conclusions: For assessment of bronchial inflammation, the bronchial methacholine provocation test (indirect marker of inflammation) is significantly correlated with NO levels (direct marker of inflammation) from exhaled air, but separately, none of these tests has significant specificity and sensibility, which results in more complex approaches that are required for diagnosis.