ABSTRACT Characterization of HLA antibody is important for donor selection for HLA matched or crossmatched blood components. 304 multiple transfused patients with neoplastic or haematological disorders were screened for HLA antibodies by the lymphocytotoxicity assay. The panel reactive antibodies (PRA) were determined against a panel of 100 lymphocytes of known HLA antigens in order to evaluate the degree of sensitization. 35 (16.7%) of the 210 male patients and 29 (30.9%) of the 94 female patients were positive for HLA antibodies. Out of the 29 positive female patients, seven patients had a history of abortion and one full term normal delivery, which suggests an anamnestic response to antigen exposure. PRA ranged from 10% to more than 90%. The specificities of identified antibodies were anti-A1, A2, A11, A24 and B55. 8 patients had multiple specificities and in 47 patients HLA specificities could not be defined.