Ten patients with perennial allergic rhinitis and 10 healthy subjects were studied to determine most discriminative nasal irrigation fluid marker(s) and to compare samples that were collected at baseline and over a 1-hour period, every 15 minutes. The latter were pooled and designated 1-hour sample. In the nasal irrigation we investigated the following inflammatory cells and soluble mediators: eosinophils, neutrophils, granulocyte-macrophage colony-stimulating factor, interleukin-4, interleukin-6, interleukin-8, ECP, EPX, MPO, leukotriene C4, leukotriene B4, prostaglandin E2, tryptase and fibrinogen. Patients with PAR were then treated for 2 weeks with the topical nasal steroid. The only marker that discriminated patients with perennial allergic rhinitis and healthy subjects was eosinophil count (EO%): correspondingly 14.01 ± 5.8 and 0.18 ± 0.09, (M ± SD). Difference between the studied groups did not depend on the time of irrigation, baseline or 1-hour. EO% was also the only marker of a clinically successful treatment with the nasal steroid, 14.01 ± 5.8 and 0.87 ± 0.4, before and after treatment respectively. We conclude that EO% is the most sensitive inflammatory marker of perennial allergic rhinitis, and that baseline nasal irrigation can be used to study nasal mucosal inflammation.