The performance of fractional exhaled nitric oxide (FeNO), blood eosinophil count (BEC), and eosinophil activity markers should be evaluated.<h4>Objective</h4>This study aimed to compare the associations of FeNO, BEC, serum and plasma eosinophil-derived neurotoxin (S- and P-EDN), and serum eosinophilic cationic protein (S-ECP) with important clinical outcomes in asthma.<h4>Methods</h4>In total, 390 individuals aged 10-35 years with physician-diagnosed asthma were included. The gene discussed is RNASE3; the disease is asthma.