The aim of this study was to investigate FOI’s ability to monitor the treatment response to TNFα inhibitor therapy with certolizumab pegol (CZP) in RA patients and to compare FOI findings to clinical outcome parameters such as DAS28 (CRP), tender joint count (TJC-28), swollen joint count (SJC-28) and laboratory parameters. Here, TNF is linked to rheumatoid arthritis.