The proliferating skin cells in a case of acute disseminated histiocytosis‐X (Abt‐Letterer‐Siwe disease) confirmed by electron microscopy, were characterized by a panel of monoclonal antibodies using an immunoperoxidase technique. The “histiocytes” were found to stain with OKT‐6 (anti‐T6) and anti‐HLA‐DR antibodies. Unexpectedly, slight staining was also observed with Leu 3a (anti‐T4) and OKM‐1. A proliferative process of T4, T6, HLA‐DR, OKM‐1 positive Langerhans' cells has not yet been described and may be spe