To investigate the expression of plasmacytoid dendritic cells (pDCs), interferon regulatory factor-7 (IRF-7) and interferon alpha (IFN- alpha) mRNA in skin lesions of patients with psoriasis vulgaris, the expressions of plasmacytoid dendritic cells, IRF-7, IFN-alpha mRNA in the lesional skin of psoriasis vulgaris were detected by immunohistochemical technique (SP) and RT-PCR. Normal skin of healthy volunteers, serving as control, was also tested. The immunohistochemical study showed that the expression of pDCs in the psoriatic lesions was significantly higher than that in the normal controls. RT-PCR showed that the mRNA expression of IRF-7 was much higher than that in normal controls, but no difference in the expression of IFN-alpha mRNA was found between two groups. Our findings indicate that up-regulated expression of pDCs, IRF-7 mRNA might be involved in the pathogenesis of psoriasis.