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immunization in patients whohave been previously immunized by pregnan-cy or transfusion is not prevented. Neither canimmunization against platelet-specific al-loantigens be prevented by removing leuco-cytes from platelet concentrates, but platelet-specific antibodies seem to occur mainly inpatients who develop HLA class I antibodies.Not all patients with HLA antibodies are re-fractory. Often the antibodies only react witha small percentage of panel lymphocytes andthen most random donors are compatible.Furthermore, although there are individualdifferences, some HLA class I antigens areweakly expressed on platelets. Nevertheless,refractory alloimmunized patients in need ofplatelet transfusions will continue to occur.Opinions on the optimal management of suchpatients differ. Moreover, some simple and in-teresting new crossmatch techniques have re-cently been developed. For these reasons itseemed of interest to devote an InternationalForum to the subject.There seem to be two main approaches tothe management of refractory patients: (I) theselection of platelet concentrates based on theHLA class I phenotype and, or the specificityof the HLA (and platelet-specific) antibodies,and (II) the selection of platelet concentratesby crossmatching.To obtain more information on the sub-ject, the following questions were submittedto 15 experts in the field