Immunoglobulin class plays an important role in the histocomatibility crossmatch test to predict hyper acute rejection in kidney transplantation. The existing data indicates that immunoglobulin (Ig) M antibodies, particularly when they are autoantibodies, are not deleterious to the renal allograft. We used the reducing agent dithiotreitol (DTT) to inactivate IgM but not IgG in the crossmatch assay to help sensitized patients have the chance for successful transplantation. In this descriptive study, 57 candidates for kidney transplantation with final positive crossmatches who had a history of panel-reactive antibody (PRA) greater than 30% were selected. Two of 57 patients had systemic lupus erythematous (SLE). The sera of patients were treated by DTT and then measured for dependent cytotoxicity against donor lymphocytes and a panel of 12 cells using the complement dependent cytotoxicity (CDC) method. Autocossmatch was also performed to differentiate autoantibodies and alloantibodies by the CDC method. Of the 57 patients, six subjects (10.53%) had IgM and 51 jpatients (89.47%) IgG in their serum against donor lymphocytes. Also against panel cells, 39 of 57 patients (68.43%) had IgG, three patients (5.26%) had IgM, and 15 patients (26.31%) had both IgG and IgM antibodies. Autolymphocytotoxic antibodies were detected in 1.75% patients (1 of 57) who had SLE. According to our results, 5.26% of the patients who were IgM-positive and IgG-negative for both crossmatch and PRA assays may experience successful kidney transplantation.