Approximately 30% of rheumatoid arthritis patients achieve inadequate response to anti-TNF biologics. In this study, we sought to identify a blood gene expression biomarker correlating with 12-week response to infliximab in patients with moderate to severe disease. Response was assessed using dynamic contrast-enhanced MRI imaging of the wrist. Overall design: Baseline whole blood samples from 59 patients were collected as part of a placebo-controlled clinical study of infliximab in rheumatoid arthritis. Samples were profiled by Affymetrix microarray and correlation between gene expression and 12-week response was assessed. DAS28 (Disease Activity Score including a 28-joint count)