In this study we describe immunotoxins prepared with different CD2 monoclonal antibodies (mAbs) and a ribosome-inactivating protein, saporin. The CD2 immunotoxins were tested on different models. Anti-CD2-saporin conjugates inhibited protein synthesis by a neoplastic CD2+ cell line (SKW-3) and by an interleukin 2 dependent polyclonal CD2+ lymphoid cell culture (T lymphoblasts), with IC50s ranging from 10(-13) M to 10(-11) M (as saporin). Similar results were obtained with proliferation inhibition tests (3H-thymidine incorporation) on phytohaemagglutinin (PHA) driven lymphoid cultures and on mixed lymphocyte culture activated lymphocytes. Moreover a CD2-ricin A chain conjugate was less effective than an analogous immunotoxin containing the same CD2 mAb and saporin in inhibiting lymphocyte proliferation induced by PHA (IC50 approximately 10(-9) M as ricin A chain versus 10(-12) M as saporin). The conjugates were not toxic on bone marrow stem cells. These results suggest that CD2-saporin immunotoxins could represent an effective tool for CD2+ lymphomas or leukaemias, and for T-dependent immune disorders, such as transplanted organ rejection and graft-versus-host disease.