The main problem in matching donor-recipient pair in kidney transplantations is sensitization of dialysed patients. The patients with high percentage of cytotoxic antibodies to peripheral blood lymphocytes from a random panel, have a low chance of receiving a renal allograft. Negative results of the crossmatch between recipient serum and donor lymphocytes is decisive criterion for kidney transplantation. However not all antibodies are harmful for the graft. We present out methods of differentiating between auto- and alloantibodies and between IgM and IgG class of alloantibodies in sera of hypersensitized patients. The precision of identification of HLA matched donors is vital in bone marrow transplantations. The standard cytotoxicity tests cannot identify all HLA class II alleles and MLC testing is a long procedure. We present our observations from introducing the PCR Fingerprinting technique for a rapid identification of the class II compatible individual among potential donors bone marrow transplant.