The very strong association of human leukocyte antigen (HLA)-B27 with spondyloarthritis might be related to its peptide-presenting properties. The natural polymorphism of this molecule influences both peptide specificity and disease susceptibility. In this study, we present a comprehensive compilation of known natural ligands of HLA-B27 arising from endogenous proteins of human cells, together with a statistical assessment of residue usage among constitutive peptide repertoires of multiple HLA-B27 subtypes. This analysis provides evidence that every peptide position, including "non-anchor" ones, may be subjected to selection on the basis of its contribution to HLA-B27 binding and also allows a quantization of residue preferences at known anchor positions. The present registry is intended as a basis on which to build up reliable criteria to assess the effect of HLA-B27 polymorphism on peptide presentation, for T-cell epitope predictions, and for molecular mimicry studies.