[en] Diagnosis of renal graft acute rejection is made mainly by clinical signs, humoral and functional changes, and is confirmed by histopathological studies. Many efforts have been made to find a radiopharmaceutical for early diagnosis of renal graft rejection. 99mTc-ior t3 monoclonal antibody was evaluated as a radiotracer in renal graft acute rejection. Schwarz's method was used with different molar relations 2ME:IgG and different tin-chelates were explored. The selected formulation was studied by chromatography and challenge studies. Once proved the quality of the radiopharmaceutical a freeze-dried Kit was performed. Its radiochemical purity and stability was studied for several months. FPLC and immunoreactivity studies were included. The sterility and apirogenicity was certified by the Center of Research and Development of Drugs. A clinical trial was started with patients who have received a renal graft eleven days before. An amount of 1.1 GBq of 99mTc-ior t3 MoAb was administered and planar scintigraphic images were recorded. A molar relation of 2000:1 (2ME:IgG) with 30 min produced the best reduction of the MoAb. From the different tin-chelates, the tin-pyrophosphate produced the highest radiochemical purities. The MoAb freeze dried Kit contains 1.0 mg of protein and 14 ug of Sn+2, this quantities guaranteed a shelf life of 6 months. The quality controls and challenge studies showed purity higher than 95.0% and a per cent of dissociation close to 20% was seen with DTPA, 80% with HSA and 48% with Cys. Our preliminary immunoscintigraphic results showed a good correlation among scintigraphy, a high rate of counts Renal Graft/Opposite side and the cause of graft loss. The small number of cases does not permit to make a definite conclusion. However, in some clinical situations the use of 99mTc-ior t3 MoAb could help as an early and specific non-invasive diagnosis of renal graft rejection. (author)