Six new DPB1 alleles were identified by PCR-SSOP methodologies in the course of a retrospective study of the role of HLA matching in the outcome of unrelated donor bone marrow transplantation. Sequencing confirmed that five of these alleles (DPB1*5901, *6801, *7101, *7201, and *7301) represent novel combinations of previously described sequence motifs in the variable regions of DPB1; the sixth (DPB1*7001) appears to result from a novel point mutation. These data support previous observations which suggest that multiple mechanisms, including segmental exchange and mutation, appear to be responsible for generating sequence diversity at the DPB1 locus. The extremely low discrepancy rate of 0.1% between the two laboratories which typed the samples, and the ability to predict the new sequences from probe hybridization patterns, indicate that SSOP is an accurate and efficient method for studying polymorphism at DPB1.