A model to study the differentiation of human oral epithelium in vivo utilizing transplantation of human tissue to nude mice has been described. Previous studies have described the epithelial cells in this model. In this study we demonstrate that 8 d after transplantation, Langerhans cells, identified as ATP-ase positive dendritic cells, have almost disappeared from the transplanted epithelium whereas at day 21 after transplantation such cells were abundant. It is suggested that the ATP-ase positive cells which reappear in the transplanted epithelium are of mouse origin.