Objectives: Variability of clinical phenotypes in childhood obstructive sleep apnoea (OSA) has prompted research for biomarkers to identify patients at risk of developing OSA-related complications. Upper airway inflammation is documented in children with OSA. Whether it is related to end-organ morbidities and systemic inflammation is under-explored. The primary objectives of our study are 1)To evaluate inflammatory biomarkers with the use of nasal epithelial lining fluid (NELF) collected by nasal strips as a representation of upper airway inflammation in children with OSA compared to non-OSA controls; 2) To evaluate the associations between NELF biomarkers with ambulatory blood pressure (ABP) outcomes in children with OSA. Hypothesis to be tested: Inflammatory biomarkers in NELF in children with OSA are altered when compared with non-OSA controls and correlated with ABP outcomes. Design and subjects: A prospective case-control study. Non-obese Chinese children aged 6-11 years old with habitual snoring (≥3 nights per week) and polysomnography (PSG) confirmed OSA (OAHI of ≥1/hour) will be recruited as cases. Non-OSA children with OAHI \< 1 event/h will be recruited as controls. All subjects will undergo evaluation including questionnaires, anthropometric measurements, PSG, 24-hour ABP measurement, blood and NELF sampling. Primary outcome measure: Profile of inflammatory biomarkers in the NELF. Analysis: Correlations between NELF inflammatory biomarkers with polysomnographic and ABP measurements will be evaluated by regression analysis. Expected results: This study will provide novel and important information regarding upper airway inflammatory biomarkers in children with OSA and their relationship with blood pressure outcomes.