The effects of lanthanum (III) (La3+) on voltage-gated sodium channel currents (I Na) in freshly dissociated rat hippocampal CA1 neurons were studied using the whole-cell patch clamp techniques. La3+ reversibly enhanced I Na in a concentration- and voltage-dependent manner. The 50% enhancement concentration (EC50) of La3+ on I Na was 9.93 μM. In addition, 10 μM La3+ shifted the steady state activation curve of I Na towards positive potential and the steady state inactivation curve towards negative potential without changing the slope factor. These results indicated that La3+ could increase the amplitudes of I Na and change the activation and inactivation courses of I Na even in very low concentration.