The expression of the interferon regulatory factor 4 (IRF-4) and the IRF-4-binding protein (IBP) in psoriatic skin lesions was investigated. The expression of IRF-4 and IBP in skin lesions of 20 patients with psoriasis vulgaris were immunohistochemically dectected. Normal skin from 10 healthy people was used as normal control. The study showed that expression of IRF-4 was increased significantly in keratinocytes and inflammatory cells in the lesions of psoriasis vulgaris than that in the normal control. The detection revealed that IBP expression in keratinocytes, lymphocytes, hair follicles, and sebaceous glands in normal skin was significantly lower than that in the lesions of psoriasis vulgaris (P<0.05). Both IRF-4 and IBP might be involved in the pathogenesis of psoriasis vulgaris.