Here we report peptide motifs of five HLA-B molecules, B*5101, B*5102, B*5103 B*5201 and B*7801. Motifs were obtained by pool sequencing of natural ligands eluted from the respective molecules expressed in C1R cells upon transfection. A number of individual ligands that could be sequenced confirmed the motifs. All five HLA-B molecules belong to the HLA-B5, B35-cross-reactive group and are closely related as indicated by similar sequences. B51 and B52 are associated with Bw4, whereas B78 is associated with Bw6. One of the HLA-B molecules investigated here, HLA-B*5101, is associated with Behçet's disease, a multisystemic inflammatory disease affecting various organs. This disease is especially frequent among the Japanese population. The subtle differences between the peptide motifs of B*5101 as compared with the motifs of the four other closely related but not disease-associated molecules could shed light on the nature of the HLA-association of Behçet's disease.