Abstract: The basal lceratinocytes and basemeat membrane zone of psoriasis were studied by monoclonal antibodis-A 420-1.2 with indirect immunofluoresccnce assay, Gordon-Sweet' silver stain and transmission electron micro-scope. We found that basal keratinocytes and basement membrane zone were injured seriously in the active stage, Gut in resting stage the injury was of mild degree, and in the convalescent stage nearly no injury was observed. It is the authots' opinion that the injury of basal kcratinoeytes and basement membrane zone correlates with the severity of the disease.