Recently, eosinophil-derived neurotoxin (EDN), also known as ribonuclease 2 or eosinophil protein X, has gained attention because of its analytical performance, stability, and quantifiability in different samples.13, 14, 15 For instance, intracellular EDN concentrations of eosinophils are higher in subjects with mild allergic asthma than in healthy subjects.16 The gene discussed is RNASE2; the disease is allergic asthma.