Background: Several studies have previously shown some factors that modify the pathogenesis of perennial allergic rhinitis (PAR). However, the association between bacterial colonization and PAR has not been well understood. Objective: We sought to study the association between superantigen-producing Staphylococcus aureus and PAR. Methods: S aureus colonization in the nasal cavity and its superantigen production were studied in 65 patients with PAR and 45 nonallergic control subjects. The nasal symptom scores of the patients were evaluated. Furthermore, we examined the response to staphylococcal enterotoxin B or toxic shock syndrome toxin 1 of peripheral blood lymphocytes from both patients and control subjects by measuring proliferative responses and production of cytokines (IFN-γ, IL-4, and IL-5). Results: The rate of nasal carriage of S aureus in the patients (44%) was significantly higher than that of the control subjects (20%, P < .01). Moreover, the rate of nasal carriage of superantigen-producing S aureus in the patients (22%) was significantly higher than that of the control subjects (6.7%, P < .05). The nasal symptom scores of the S aureus –positive patients were significantly higher than those of the S aureus –negative patients (P < .05), although there was no significant association between symptom scores and superantigen production. Peripheral blood lymphocytes from the patients showed significantly higher proliferative responses and were more likely to produce T_H2 type cytokines in response to superantigens (P < .01), but the responses were not different among the patients with S aureus carriage and superantigen production. Conclusion: This study suggests that PAR leads to a higher carriage rate of S aureus , and nasal carriage of S aureus may aggravate PAR. (J Allergy Clin Immunol 2000;105:449-54.)