The experience in organizing the HLA class I typed donors registry and practical application for platelet transfusions in immunized patients is presented. It appears that the registry containing 3461 donors gives quite a high possibility of finding a compatible or partly compatible HLA donor for a patient with relatively high frequency antigens. A discrepancy is, however, observed between finding a donor in the registry and the transfusion of the matched platelets. Better collaboration between physicians and persons organizing the registry is required to improve transfusions of the matched platelets in immunized patients. Preliminary experience is also described concerning the usefulness of the same registry for finding the HLA class I compatible donors for bone marrow transplantation.