Objective To investigate the relationship of the expression of phosphatidylinositol-3-kinase(PI3K)subunits,P85 and P110 to the pathogenesis of psoriasis.Methods Immunohistochemical staining for P85 and P110 was performed in the tissue specimens from patients with psoriasis(n=30),chronic dermatitis(n=20),seborrheic keratosis(n=20),squamous cell carcinoma(n=20),basal cell carcinoma(n=30)and normal human controls(n=10).The absorbance of immunostained tissue was quantified with image analysis system (Q550CW,Leica,Manheim,Germany).Statistical analysis was carried out by ANOVA,Results Among these groups,a significant difference was observed in the expression level of P110 in the epidermis(F=35.64,P＜0.01),as well as in that of P85(F=59.98,P＜0.01)and P110(F=323.23,P＜0.01)in the lymphocytes infiltrating the lesion.Increased expression of P110 was found in the epidermis of psoriatic lesions compared with the lesions in the other disorders,whereas no significant difference was noticed among the other disorders.In the case of P85 and P110 expression in the lesion-infiltrating lymphocytes infiltrating the lesion,psoriasis and squamous cell carcinoma significantly differed from the other disorders,while no difference was observed between psoriasis and squamous cell carcinoma (P＞0.05).Conclusions The high expression of P110 might be closely correlated to the hyperproliferation of keratinocytes;but filrther study is needed to clarify the relationship of increased expression of P85 and P110 to the activation and proliferation of lymphocytes in psoriatic lesions.