40 mM (1%) lidocaine is usually used for infiltration anesthesia for surgical operations. Lower concentrations (1-20mM) of lidocaine were sufficient to suppress the invasive ability of cancer cells14. One mM lidocaine inhibited the invasive ability of HT1080 cells by about 50%, and 20 mM lidocaine inhibited the invasion ability completely. Lidocaine also inhibited dose-dependently the invasive ability of HOS and RPMI-7951 cells, although it was less effective on HOS cells. Lignocaine exerts its anesthetic action by obstructing the sodium channel 16 however, 10 mMof tetrodotoxin (TTX), a specific sodium channel inhibitor, had little effect on the invasive ability of HT1080 cells. Ten mM lidocaine-N-ethylbromide (NEB), which does not cross the cell membrane, also had little effect on the invasive ability of the cells.