Levels of inflammatory cytokines are higher in RA compared with OA sera. Cytokines whose levels differ significantly between sera from individuals with osteoarthritis (OA) and sera from individuals with rheumatoid arthritis (RA) (FDR < 10%). Significance analysis of microarrays (SAMs) was used to identify statistically significant differences, and the SAM-generated results were subjected to unsupervised hierarchic clustering. Cytokine levels were measured with a multiplex bead-based immunoassay. Samples from individual patients are listed above the heatmap, and the individual cytokines are listed to the right of the heatmap. IL, interleukin; IL-1ra, interleukin-1 receptor antagonist; FGF, fibroblast growth factor; MCP, monocyte chemotactic protein; HGF, hepatocyte growth factor; MIP-1, macrophage inflammatory protein; M-CSF, macrophage colony-stimulating factor; SCGF-β, stem cell growth factor β; G-CSF, granulocyte colony-stimulating factor.