Abstract: In this paper, we report the observations on the different genotypes of epidermal Langerhans cells (LC) within the skin grafts and chimeras detected with anti-Ia monoclonal antibodies. The results showed that most of the native LC within the grafts were rapidly replaced by the host LC, whereas some LC of graft origin persisted. Therefore, it is indicated that there might be two subsets of LC, a frequently mobile one and a persistent (>249 days) one. The results also showed that LC of donor genotype could be detected without exception within the epidermis of the chimeras made by bone marrow or spleen and lymph node cell injection. Thus, we propose that this new procedure be used in animal experiments and clinical studies as a simple and precise method for the detection of chimerism.