OKT3 monoclonal antibody has proved to be a potent immunosuppressive agent in treating refractory heart allograft rejections. Recently, however, an increased incidence of lymphoproliferative disorders after OKT3 therapy has been found. This short report describes the rapid growth of a cutaneous neuroendocrine (Merkel Cell) carcinoma, a rare tumor of the dermis promoted by OKT3 administration. Because OKT3 therapy seems to be associated with an increased incidence of neoplasms, frequent patient follow-up is essential.