A quantitative determination of myeloperoxidase (MPO) concentration was performed in the nasal secretions of atopic patients (challenged group, n = 17) after nasal allergen challenge outside the pollen season, and of patients with ongoing seasonal (seasonal group, n = 40) and with perennial (perennial group, n = 30) allergic rhinitis. The concentrations of MPO obtained from 10 nonallergic healthy volunteers (control group) were used as a normal control. Results showed that there was no statistical difference between the normal controls (median: 2.0 micrograms/g) and the atopic patients (median: 1.7 micrograms/g) outside the pollen season. After nasal allergen challenge (challenged group), there was no significant difference of MPO at 5 min (median: 1.0 microgram/G), 8 h (median: 1.7 micrograms/g), and 24 h (median: 3.1 micrograms/g) after challenge as compared to the baseline values. Also, there was no significant difference between patients with ongoing seasonal (median: 1.3 micrograms/g) or perennial (median: 1.8 micrograms/g) rhinitis, and atopic patients outside the pollen season. In conclusion, this study showed that MPO is not locally elaborated in measurable quantities in nasal secretions after nasal allergen challenge and during natural allergen exposure. Further studies will be needed to elucidate the role of neutrophils in the pathophysiological processes of allergic rhinitis.