Matching for human leukocyte antigen (HLA) loci is the most crucial factor in the selection of bone marrow donors. The techniques utilized to assign HLA type have evolved significantly since the application of polymerase chain reaction-based methodologies. A significant challenge for DNA typing methodologies is to be able to maintain high resolution typing with the ever-increasing numbers of defined HLA alleles. To date, over 800 HLA class I and class II alleles have been identified by sequencing analysis, and this number shows no sign of reaching a plateau. It is only with high allelic level resolution typing analysis that an accurate definition of the role that individual HLA loci play in determining transplant outcome can be achieved, and this is a major goal for the future.