To study the development of the psoriatic lesion, biopsies were taken from the margin of spreading plaques and acute pinpoint papules. Consecutive sections across the margin were stained using different monoclonal antibodies to characterize epidermal growth (Ki-67) and abnormal keratinization (Ks8.12, RKSE60). All three immunohistochemical markers showed pronounced changes in the lesional skin with a clear transition to the uninvolved skin. The suprabasal Ks8.12 binding was the earliest change found in the epidermis, and its localization high in the suprabasal compartment indicates that metabolic dysregulation in this cell population was not a consequence of the recruitment process in the basal layer.