To diminish the specific lymphocytes that responsive to the rejection of allograft. Anti-rat CD4,CD8 monoclonal antibodies and trichosnthin (TCS) was conjugated to immunotoxin by heterobifunctional reagent SPDP, 2-IT. The free TCS was removed from conjugates mixture by a column of Sephacryl S-200. The SDS-PAGE and cytotoxic assay was used to measure the biological activity of immunotoxin. SDS-PAGE showed the immunotoxin, free McAb and TCS were in the mixture of conjugation, and the free TCS can be separated by Sephacryl S-200. In Vitro, the lymphocytes of rat can be killed by antiCD4,antiCD8 immunotoxin. The kill capability was relay to the amount of immunotoxin. The authors consider that the immunology unresponsiveness can be induced by antiCD4,antiCD8 immunotoxin. That was useful in induced transplantation tolerance.