SUMMARYIntact and splenectomized mice were given full thickness skin allografts and tetanus toxoid and then treated with several immunosuppressive agents singly and in combination. Both allograft rejection and humoral antibody production were suppressed in a similar proportion of animals by similar treatment protocols. Splenectomy potentiated depression of the cellular and humoral response in mice treated with one agent. A radiosensitive cell essential to humoral and cellular immunocompetence may have been the common target affected in both types of immunosuppression.