Objective To investigate the role of nentrophils in the pathogenesis of psoriasis vulgaris. Methods Neutrophils were isolated from venous blood samples of 25 patients with psoriasis vulgaris (including 13 cases of active psoriasis and 12 cases of inactive psoriasis) as well as 25 normal human con-trols, and cultured. Then, these neutrophils were grouped and treated with lipopolysaccharide (LPS, 100 g/L),CpG-A (50 mg/L), CpG-B (50 mg/L), and RPMI 1640 culture medium, respectively, for 24 hours followed by the collection of culture supematants. Human keratinocytes (HaCaT) were cultured in the presence of su-pematants of treated or untreated nentrophils for 72 hours followed by the detection of cell proliferation with MTT assay. To determine the role of proinflammatory factors, SOD/CAT and monoclonal antibody to IL-8 and TNF-alpha of 400 u/mL were used to pretreat HaCaT cells 1 hour prior to the stimulation with super-natants of neutrophils. Results Compared with culture medium, the supematant of unstimulated neutrophils from normal controls or patients with inactive psoriasis had no significant effect on the proliferation of HaCaT cells (P ＞ 0.05), but that from patients with active psoriasis markedly promoted the proliferation of HaCaT cells (t = 2.41, P < 0.05). ARe, stimulation by LPS, CpG-A and CpG-B, the supematant of active patient-derived neutrophils significantly promoted the proliferation of HaCaT cells compared with that of normal control-derived nentrophils (t = 3.11, 2.89, 2.29, respectively, all P < 0.05). In comparison with tmstimulated neutrophils, the supematant from LPS- and CpG-A stimulated nentrophiles significantly accelerated the pro-liferation of HaCaT cells. Furthermore, the proliferation of HaCaT cells induced by the supematants of LPS-,CpG-A-, CpG-B-stimulated neutrophils from psoriatic patients was statistically suppressed by the pretreat-ment with the monoclonal antibody to IL-8, TNF-alpha and SOD/CAT (all P < 0.05). Conclusions In patients with psoriasis vulgaris, there is an abnormal secretion of IL-8, TNF-alpha and superoxide by neutrophils in peripheral blood, and these proinflammatory factors could promote the proliferation of HaCaT cells.