A quantitative determination of the inflammatory mediators was performed and correlated with complaints and the measurement of the inflammatory cells in nasal secretions of 18 seasonal allergic rhinitis patients (group 1) outside the pollen season and 40 symptomatic patients (group 2) with seasonal allergic rhinitis during the pollen season. Ten nonallergic subjects (group 3) were also studied as a normal control group. In group 1, 17 (94%) out of 18 patients had an immediate response of nasal symptoms accompanied by a significant increase of histamine, leukotriene C4 (LTC4), and tryptase 5 min after nasal allergen challenge (NAC). One hour later, a simultaneous increase was seen both in the percentage of the eosinophils and in the eosinophil cationic protein (ECP) concentration. The eosinophil count reached a peak 2 h after NAC with a duration of 8 h, while the highest ECP level was reached only after 24 h with no clear-cut plateau. In group 2, a high percentage of eosinophils was observed. Mostly one observed significantly (p < 0.01) higher concentrations of ECP, LTC4 and histamine but not of tryptase than the baseline values of group 1. The authors concluded that during the pollen season allergic rhinitis reflects mainly a chronic state of allergic inflammation of the nasal mucosa involving various inflammatory components induced by one or more episodes of early-phase type allergic reaction. Infiltration of eosinophils and consequently release of the various late-phase inflammatory mediators into the nasal secretions are certainly believed to be the predominant pathophysiologic condition in the patients.