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Background: Activation of T cells is believed to play a critical role in the pathogenesis of psoriasis. Recently, it has been proposed that psoriasis is a T-cell-mediated autoimmune reaction triggered by bacterial superantigen., Objective: We investigated whether patients with chronic plaque psoriasis bear superantigen-producing Staphylococcus aureus on the skin or the throat., Methods: S. aureus producing exfoliative toxin, staphylococcal enterotoxin B or toxic shock syndrome toxin 1 was isolated from the skin and throat of 100 psoriasis patients using Western blot analysis and polymerase chain reaction., Results: Only 5, 4 and 9 patients had super-antigen producing S. aureus identified on lesional skin, nonlesional skin and throat, respectively. The vast majority of patients did not bear superantigen-producing S. aureus., Conclusion: We believe that superantigens are not essential in sustaining disease activity but may, instead, be exacerbating or triggering factors for some psoriasis patients.