The activities of interleukin 6 (IL 6) and tumor necrosis factor alpha (TNF?) produced by peripheral blood mononuclear cells (PBMCs) in vitro and their relevant levels in sera were measured in 49 patients with psoriasis vulgaris (PV) and in 20 normal controls using bioassay. The relationship between them was also analysed. The results showed that in PV patients the activites of IL 6 and TNF? produced by PBMCs and their serum levels were higher than those in healthy controls. There was a positive linear correlation between the activites in vitro and relevant levels in sera, and a positive linear correlation between serum levels of IL 6 and TNF?. These results indicate that there is dysfunction of cellular immune of PBMCs in PV patients. The increase of serum levels of IL 6 and TNF? may be related to the increased activity of PBMCs, and there may be a synergic action between IL 6 and TNF? in the pathogenesis of psoriasis.