The pathophysiology of allergic rhinitis induced by various inhalant allergens through an IgE mediated mechanism, has been well demonstrated. The participation of many important inflammatory cells and mediators released by these cells in the human nasal allergic reaction provides insight into the relationship between the responsiveness to allergen exposure and nasal symptoms of allergic rhinitis. This paper summarizes our previous studies on some important mediators in the nasal secretions of atopic patients during different phases after nasal allergen challenge and during natural allergen exposure. The microsuction technique proves to be an especially useful and reliable nasal sampling method permitting quantitative analysis of important mediators such as histamine, tryptase, leukotriene C4 and eosinophil cationic protein in nasal secretions. The measurement of these mediators during allergic reactions provides accurate data on the activity of some important inflammatory cells (i.e., mast cells, basophils, and eosinophils) and their responses to therapy.