To evaluate the contribution of peripheral blood monocytes (PBMC) to epidermotropic inflammatory reactions in psoriasis, using an enzyme-linked immunosorbent assay we measured spontaneous interleukin-8 (IL-8) production in PBMC obtained from patients with psoriasis. IL-8 production in the psoriatic PBMC was significantly higher than that in normal control PBMC. Plasma IL-8 levels in psoriatic patients were also moderately increased compared to normal control levels. IL-8 production in PBMC was closely related to the clinical severity of psoriasis and to the response to treatment, including systemic methotrexate (MTX) treatment and tonsillectomy. IL-8 production in PBMC was also positively related to the production of interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) in these cells. We speculate that the chemotactic cytokine IL-8 contributes to the development of psoriatic skin lesions, and mediates inflammatory reactions from the inflammatory focus to the psoriatic lesions.