Objective: To observe the expression of CD13/APN in peripheral blood lymphocytes and skin lesions of patients with advanced psoriasis vulgaris

and discuss its effect on the pathogenesis of psoriasis. Methods: CD13 expression in peripheral blood lymphocytes and skin lesions was detected by flow cytometry and immunohistochemical technique

respectively. Results were compared with those of healthy controls. Results: CD13 expression was significantly higher in peripheral blood lymphocytes of patients with advanced psoriasis vulgaris than in that of healthy controls

and in skin lesions than in healthy skin tissues. The expression was mainly in the suprabasal layers of skin lesions

and positively correlated to PASI （R=0.78029）. Conclusion: The significantly higher expression of CD13 in peripheral blood lymphocytes and skin lesions of the patients with advanced psoriasis vulgaris probably is related to immunological abnormality

blood vessel abnormality and proliferation of keratinocyte in the pathogenic course of psoriasis. It may be a novel and effective way to treat psoriasis with specific CD13 inhibitors.