Using the monoclonal antibody Ks8.12 directed against keratins 13 and 16, we have studied psoriatic and trauma-induced hyperproliferation. In normal skin 40 and 64 h after sellotape stripping and in psoriatic lesions, a pronounced suprabasal staining by Ks8.12 was observed. In unstripped normal skin and in the clinically uninvolved skin of psoriatic patients some patchy staining limited to the basal layer was seen. The clear distinction between normal and hyperproliferative skin in keratin expression as detected by Ks8.12 indicates that this antibody may serve as a marker for epidermal proliferation in psoriasis.