Abstract： Intrathymic (IT) inoculation of allogeneic major histocompatibility complex (MHC) soluble antigen extracted from C57BL/6 inbred mice splenocytes using 3mol/L KCl was performed to induce donor-specific tolerance to skin allografts in adult BALB/C mice. The recipients (BALB/C) received anti-T lymphocyte monoclonal antibodies (mAb) 8.4μg on 0 and 3rd day relative to IT injection of allogeneic MHC antigen without other immunosuppressant. The control group received anti-T lymphocyte mAb 8.4μg but IT injection of normal saline (NS). Median survival time (MST) of transplanted skin allografts was 83 days in tolerant recipients while normally rejected 3rd-party CBA/J skin grafts (MST 12 days). In the control group, skin grafts'MST was 11 days. Responder cells of tolerant recipients to C57BL/6 stimulators showed significantly less incorporation in oneway mixed lymphocyte reaction but in normal fashion to third-party CBA/J stimulators. The results suggested that unresponsiveness can be induced by IT inoculation of soluble allogeneic MHC antigen which was donor-specific.