Tissue factor (TF) is expressed in atherosclerotic lesions. Since mechanical forces influence endothelial cell (EC) function and are thought to account for the unique distribution of atherosclerosis in areas exposed to disturbed flow, we hypothesized that disturbed to-fro flow (TFF) and unidirectional pulsatile forward flow (PFF) would have different effects on TF expression in EC. TF RNA expression in HUVEC exposed to mechanical stress in the presence or absence of chemical stimulation with thrombin was determined. TFF induced a significantly higher TF expression than PFF that was sustained for 8 h. Combination of mechanical and chemical stimuli induced significantly higher TF expression than only mechanical stresses, and this effect was synergistic in both TFF and PFF. The MAPK p38 inhibitor SB-203580 significantly inhibited TF expression induced by mechanical and chemical stimulations, but the MEK inhibitor PD-98059 did not inhibit TF induced by TFF. Immunoblotting revealed that ERK1/2 phosphorylation induced by TFF was sustained for 120 min, whereas that induced by PFF was not. We conclude that disturbed flow induced greater and sustained amplification of TF expression, and this synergistic effect may be regulated by p38 MAPK and ERK1/2. These results provide added insight into the mechanism of atherosclerosis in areas of disturbed flow.