Objective To compare the changes of 11 cytokines in ankylosing spondylitis(AS)before and after treatment with a loading regimen of infliximab and to evaluate the potential AS related discriminating cytokines and explore their value in diseases activity evaluation and possible association with therapeutic response.Methods This was an open-labeled,phase Ⅱ clinical trial conducted in 2 medical centers.All AS patients were infused with infliximab at week 0,2,6.The dosage was 5 mg/kg.Disease activity parameters were assessed at week 0,2,6 and 10.Eleven serum cytokines were detected using protein chip technique,then,serum IL-6 level wag measured by sandwich enzyme-linked immunosorbent assay(ELISA).Results IL-6 was detected by EHSA.Compared with healthy controls.IL-6 level incregsed markediy in AS(P<0.01).After treated with infliximab,IL-6 level decreased at week 2(P<0.01)and maintained at low level until week 10.Baseline serum IL-6 level was positively associated with AS disease activity index(night pain scores、ESRand CRP)(P<0.01).Conclusion Serum IL-6 level is associated with AS disease activity and may become a useful parameter for monitoring the clinical response of infliximab in AS patients.IL-6 is an important cytokine involved in the pathogenesis of AS.