Synovitis, which is characterized by the infiltration of inflammatory cells, often accompanies progression of temporomandibular joint disorder (TMD) symptoms. Because IL-1 beta is elevated in synovial fluids obtained from TMDs, we hypothesized that IL-1 beta-responsive genes in synoviocytes may help identify the putative genes associated with synovitis. Using microarray analysis, we found that monocyte chemoattractant protein-1 (MCP-1) mRNA levels were elevated in IL-1 beta-stimulated synoviocytes. MCP-1 is a member of the chemokine superfamily. The production of MCP-1 was increased in synoviocytes treated with IL-1 beta. When IL-1 beta was injected into the cavities of rat TMJs, inflammatory cells and MCP-1-positive cells were detected in the synovial tissues. Furthermore, MCP-1 levels were higher in synovial fluids from individuals with pain compared with those without pain. Inhibitors of MAP-kinases and NF-kappa B reduced IL-1 beta-induced MCP-1 production. These results suggest that MCP-1 stimulated by IL-1 beta is one of the factors associated with the inflammatory progression of TMDs.