Bone marrow transplantation is an effective therapy for a variety of genetic and hematologic disorders. Donated bone marrow, which provides a source of stem and progenitor cells for bone marrow reconstitution, is obtained either from related donors, usually HLA-matched siblings, or from HLA-matched unrelated donors. Because of the limited availability of HLA-matched related donors, HLA-matched unrelated donors are frequently the only alternative source of bone marrow for transplantation. To provide matched volunteer bone marrow donors for unrelated recipients, the National Marrow Donor Program (NMDP) was established in 1986 to develop a national Registry of HLA-typed individuals who agree to donate bone marrow if needed. More than 3 million potential marrow donors are now enrolled. A limitation of the registry approach is the time needed to identify a donor and complete the necessary clinical evaluation and laboratory testing for histocompatibility, infectious diseases, and general good health. Moreover, a certain proportion of potential donors change their minds or otherwise become unavailable between the time they enter the Registry and the time they are called as a preliminary match for a patient. Another disadvantage is the marrow harvesting procedure which requires the normal donor to be hospitalized and given general anesthesia in an operating room. Finally, the NMDP Registry consists of potential donors that are primarily of European Caucasian ancestry. Although great strides have been made in increasing the numbers of African-Americans, Hispanics, Asian-Americans, and Native Americans, it is still more difficult to find matches for these ethnic minorities than for Caucasian patients.