Background Psoriatic plaques present a complex expression profile, including high levels of cytokines, chemokines and growth factors. Circulating cytokines have been suggested to reflect the activation status of the inflammatory process. Objectives To analyse 20 cytokines, chemokines and growth factors in 14 patients with psoriasis vulgaris at the start and during the course of ultraviolet B treatment. Methods A multiplex cytokine assay was used. Results We identified increased serum levels of epidermal growth factor (EGF) (mean 323 vs. 36 6 pg mL(-1), P = 0 0001), interleukin (IL)-1 receptor antagonist (mean 39 1 vs. 14 6 pg mL(-1), P = 0 02) and tumour necrosis factor-alpha (mean 7 5 vs. 4 5 pg mL(-1), P = 0 04) at baseline in patients with psoriasis compared with matched controls. None of these cytokines was correlated to the severity of the disease (Psoriasis Area and Severity Index) or decreased with phototherapy, suggesting that sources other than lesional skin contribute to the production of these cytokines. Using cluster analysis, we observed coordinate upregulation of EGF, IL-6, macrophage inflammatory protein-1 beta and vascular endothelial growth factor. Conclusions The sustained high expression of inflammatory circulating cytokines is a potential mechanism linking psoriasis with its extracutaneous comorbidities.