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1. Maniscalco M (2017) Nasal nitric oxide as biomarker in the evaluation and management of chronic rhino-sinusitis with nasal polyposis. Eur Arch Otorhinolaryngol. doi:10.1007/ s00405-017-4591-y 2. Yao Y, Xie S, Yang C, Zhang J, Wu X, Sun H (2017) Biomarkers in the evaluation and management of chronic rhinosinusitis with nasal polyposis. Eur Arch Otorhinolaryngol. doi:10.1007/ s00405-017-4547-2 3. Phillips PS, Sacks R, Marcells GN, Cohen NA, Harvey RJ (2011) Nasal nitric oxide and sinonasal disease: a systematic review of published evidence. Otolaryngol Head Neck Surg 144:159–169 4. American Thoracic Society, European Respiratory Society (2005) ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. Am J Respir Crit Care Med 171:912–930 5. Vaidyanathan S, Williamson P, Anderson K, Lipworth B (2010) Effect of systemic steroids on humming nasal nitric oxide in chronic rhinosinusitis with nasal polyposis. Ann Allergy Asthma Immunol 105:412–417 Dear Editor,