SUMMARYThe epidermis in lichen planus presents an apparently paradoxical situation. There are on the one hand epidermal hypertrophy acanthosis and hypergranulosis, and on the other, destruction of the generative compartment with erosion of the basal layer. In order to understand how the two processes can co‐exist, thirty‐five lichen planus papules from twenty‐five patients were injected intracutaneously with IO μ Ci of tritiated thymidine. Sixteen of these lesions were removed after 50‐60 min and nineteen were removed after longer intervals of up to 10 days. Autoradiographs prepared from biopsied lesions demonstrated that keratinocytes had migrated into the lichen planus lesion from the intact margins, replaced the eroded basal layer and repopulated the epidermis of the lesion. It is concluded that the changes observed in the epidermis seen in lichen planus can be interpreted as the result of a continuous process of (1) erosion and (2) repopulation in an attempt at healing of the woun