The expression of CD 44 in psoriatic epidermis was studied with immunohistochemical staining. Overexpression of CD 44 was observed in involved proliferative epidermis as compared with uninvolved and cured epidermis in psoriatic patient. Several CD 44 isoforms based on analysis by reverse transcriptase polymerase chain reaction (RT PCR) were mainly CD 44 S and CD 44 E. These results suggest that CD 44 may be an important substance in the proliferation of keratinocytes, such as psoriasis.