OBJECTIVES:To investigate the relation between ankylosing spondylitis disease activity score (ASDAS), Bath ankylosing spondylitis disease activity index (BASDAI) and treatment response and biomarkers of inflammation (C-reactive protein (CRP), interleukin-6 (IL-6), YKL-40), angiogenesis (vascular endothelial growth factor (VEGF)), cartilage (C-terminal crosslinking telopeptide of type II collagen (CTX-II), matrix metalloproteinase-3 (MMP-3), total aggrecan, cartilage oligomeric matrix protein) and bone (C-terminal crosslinking telopeptide of type I collagen, osteocalcin) turnover in 60 patients with axial spondyloarthritis initiating tumour necrosis factor alpha (TNFα) inhibitor therapy. METHODS:ASDAS (CRP-based), BASDAI and biomarkers were determined before and seven times during 46 weeks of TNFα inhibitor therapy. RESULTS:Very high ASDAS were associated with high levels of inflammatory biomarkers, while high BASDAI were not related to any biomarkers. Mixed modeling demonstrated significant longitudinal associations between ASDAS and IL-6, VEGF, MMP-3 and osteocalcin and between BASDAI and CRP, IL-6 and VEGF. Major improvement in ASDAS was associated with larger percentage decreases in biomarkers of inflammation, angiogenesis, MMP-3 and increases in aggrecan and osteocalcin. BASDAI response was associated with larger decreases in CRP and IL-6. Biomarkers with moderate/high differences in responsiveness for major versus no/clinically important improvement in ASDAS were CRP, IL-6, VEGF, aggrecan and osteocalcin, and VEGF and CTX-II for BASDAI response versus non-response. CONCLUSION:Levels and changes of 10 biomarkers in patients with axial spondyloarthritis during anti-TNFα therapy were documented. Construct validity and responsiveness of IL-6, VEGF, MMP-3, total aggrecan and osteocalcin were demonstrated. ASDAS was more associated with these biomarkers than BASDAI, and may better reflect the inflammatory disease processes. ClinicalTrials.gov identifier NCT00133315.