Objectives: The pathophysiology of idiopathic rhinitis is unknown. The condition is often termed non-allergic rhinitis because patients are skin-prick test negative with normal serum IgE yet this only means that patients are in fact non-atopic. The absence of atopy does not exclude the possibility that idiopathic rhinitis is caused by a localized allergic inflammatory cascade. This study was designed to test the null hypothesis: That patients with idiopathic rhinitis have no significant difference in their allergic parameters when compared to allergic and normal controls. Methods: Over a 4-year period, using a meticulous selection algorithm, 3 groups (idiopathic rhinitis, allergic rhinitis and normal controls) of pure steroid-free patients (n = 56) were recruited into a specialized rhinitis research clinic. Nasal smears, full-thickness mucosal biopsies, serum samples, and detailed nasal challenge results were obtained. Smears were stained to detect eosinophilia. Turbinate tissue was both frozen and fixed in formalin for immunocytochemistry, in-situ hybridization, and polymerase chain reaction analysis. Serum was analyzed for the presence of auto-anti-IgE antibodies. Nasal challenges were performed to normal saline solutions and 5 perennial aero-allergens. Results: The allergic rhinitis and idiopathic rhinitis groups had raised eosinophil smears and higher epithelial mast cell and IgE+ cell numbers compared with normal controls (P < 0.05). Tissue plasma cell and eosinophil numbers were similar in the 3 groups. 100% of the allergic group and 52% of the idiopathic group had abnormal nasal challenge results compared with 0% of controls (P < 0.05). 88% of allergic patients had auto-anti-IgE in their serum compared to 0% in both the idiopathic and normal control groups (P < 0.01). Conclusion: Steroid-free patients with pure idiopathic rhinitis show a similar allergic inflammatory cascade in nasal tissue when compared to patients with allergic rhinitis (power > 90%). These nasal findings are not present in normal control patients. Patients with idiopathic rhinitis and normal controls do not show any systemic markers of atopy, in contrast to patients with allergic rhinitis.