The selection of platelet donors, according to HLA antigens, has been computerized using a method based on the calculation of incompatibilities and risk of immunization between donors and recipients. Since the risk that an antigen present in a donor will immunize an incompatible recipient of known HLA phenotype, an incompatibility score is established and a donor file printed out, ranked according to the degree of incompatibility. The principle of this method is valuable for any other compatibility system and can be easily extended according to the computer potency. The method allows a rapid selection of the most appropriate plateletpheresis donors to avoid immunizing unsensitized patients or to achieve the best degree of compatibility in previously sensitized patients.