Studies from around the world have confirmed the association between HLA-B27 and human spondyloarthropathies. The onset of many HLA-B27-linked arthritides follows an infection with enterobacteria. How bacteria interact with HLA-B27 and modify the immune system to give rise to the clinical disease is currently unclear. The roles of other genetic factors, including major histocompatibility complex class II genes and other genes located within this region (Tap/Lmp), have been postulated in certain spondyloarthropathies. We are using transgenic and knockout mice to answer some of these unsolved issues. This review discusses recent findings from our laboratories.