As a result of an appeal for a bone marrow donor for a North American Indian (Native American) patient, 261 Native Americans from our community were typed for HLA-A,B,DR antigens, and 51 were typed for HLA-A,B antigens only. The HLA antigen frequencies of the Native Americans were compared with those of 12,881 white bone marrow donors and were found to differ markedly. To investigate the implications these differences in HLA antigen frequencies would have for the location of unrelated bone marrow donors, the HLA types of 12 Native American bone marrow transplant patients from our institution were used to search among 5389 HLA-A,B,DR-typed white donors in the National Marrow Donor Program file and the file of 261 HLA-A,B,DR-typed Native American donors. In the white donor file, at least two donors were found that matched at all HLA-A,B,DR antigen loci of one Native American patient (8%). Using the Native American donor file, which was less than one-twentieth the size of the white donor file, and HLA-A,B,DR-matched donor was also found for one (8%) of the patients. These results suggest that although donors for nonwhites can be identified in a file of HLA-typed white volunteers, the probability of finding a suitably matched donor for such individuals is enhanced if donors representing racial or ethnic minorities are included in unrelated donor registries.