Eight 15I5 B-congenic White Leghorn chicken lines, containing haplotypes B2, B5, B12, B13, B15, B19, and B21, were subjected to molecular genotyping with chicken B-F (Class I) and B-L (Class II) major histocompatibility complex (MHC) probes. Genomic DNA was digested with restriction enzymes, hybridized with a Class I or Class II probe, and analyzed for restriction fragment length polymorphisms. Digestion with HindIII or EcoRI yielded no B-L polymorphisms. Digestion with PvuII or BglII and hybridization with a B-L or B-F probe produced polymorphisms that were shared between several haplotypes, although the haplotypes with similar patterns were clustered differently between Class I and Class II probes. The genetic variation seen for B-L and B-F probe hybridization of PvuII digests was much less than that previously demonstrated for B-G probing of PvuII digests of the same lines. Description of MHC Class I and II restriction patterns of the well-characterized 15I5 B-congenic lines will aid in identification of genes important in disease resistance.