Electrically activated silver was shown to have an antibacterial effect in vitro and in vivo. In this study the effect of placing a silver anode in the root canal systems of teeth was examined to establish a base for treatment of infected teeth. Pure silver wires were placed in the main canals of extracted human teeth (n Å 26) whose roots were partly submerged in a lactated Ringer's solution. Seventeen microamperes of anodic direct current were applied to one group of silver wires (n Å 15) for 4 days. Then the wires were removed and the roots of both group teeth were cut into six sections and demineralized. Silver concentrations of the root sections and their bathing solutions were measured with an atomic absorption spectrophotometer. In the anode group, the electrically activated silver concentrations (range, 1-30 mg/mL) exceeded the antibacterial levels (minimum inhibitory concentration, 0.1 mg/mL Ag) in all sections, particularly in the middle and lower sites of the root. The amount of anodic silver that leaked out of the root was found as to be 0.4 { 0.2 mg/mL in the fluid medium. This was 10 to 100-fold higher than that found in the nonactivated controls.