In spondyloarthritis, in particular ankylosing spondylitis (AS), a need exists for clinically meaningful biomarkers, both for diagnosis and prognosis. Earlier diagnosis has become an imperative since the advent of biologic therapy, which has proved effective in controlling axial inflammation. Presently, however, there are no biomarkers that reliably distinguish inflammatory back pain from the far more prevalent mechanical back pain. The target sites in AS--sacroiliac joints and the spine--are relatively inaccessible to the investigator and clinician, so defining markers associated with or predictive of axial inflammation remains an important goal. Cytokines, metalloproteinases, and cartilage catabolic products are all candidates for the important role of biomarker in spondyloarthritis.