The IL-2 receptor system is a suitable target for immunotherapy in conditions in which activated (T) cells play a pivotal role, such as transplantation reactions and auto-immune diseases. Antibodies directed at the IL-2R can be used as such or modified by conjugation to toxins or through chelators to radiolabels. These antibodies have, however, the disadvantage that the recipient may mount an immune response against it, thus limitng its therapeutic use. A novel therapeutic modality may be the IL-2 toxin conjugates; these conjugates seem to be more effective in vitro and in vivo than the MoAbs. Specific immunotherapy through the IL-2 receptor constitutes a rational, novel, specific and highly promising therapeutic modality for conditions in which IL-2R plays a pivotal role, such as transplantation rejections and auto-immune diseases.