In this study, we investigated the synergistic effects of Staphylococcus aureus extracts (membranes and walls) and lipopolysaccharide (LPS) derived from Escherichia coli on tumor necrosis factor (TNF) production in the pathogenesis of silica-induced inflammation. The synergistic induction of TNF by silica particles $(<20;{mu}m)$ in combination with either S. aureus extracts or LPS was examined in J774A.1 cell cultures. Media from the treated and untreated cell cultures were assayed for TNF, using the mouse WEHI 164 cell cytotoxicity assay and enzyme immunoassay. Cells exposed simultaneously to silica and $0.5;{mu}g/ml$ S. aureus extracts (or 0.5 ng/ml of LPS) produced a significantly higher level of TNF than those produced by the inducer alone. Our results indicate that device-associated infections (or pyrogen contamination) could enhance inflammatory responses, because of particles produced by the wear of medical implants or particulate biomaterials used for clinical purposes.