The effect of sodium metabisulfite (SMB) on voltage-gated sodium channel currents (I(Na)) was examined in freshly isolated rat hippocampal CA1 neurons using whole-cell patch-clamp technique under voltage-clamp conditions. SMB irreversibly enhanced I(Na) in a concentration-dependent manner, shifted the inactivation curve to more positive potential, without affecting the current activation curve. In addition, SMB increased the time to peak and the inactivation time constant of I(Na). Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) could all partly inhibit the effect of SMB on the sodium current. These results suggested that SMB have neuronal toxicity by increasing the excitability of neurons and its mechanism might involve the oxidative damage on ion channels.