Using whole-cell configuration of patch clamp technique we found that mexiletine (Mex) reversibly inhibited the sodium current in a voltage- and use-dependent manner in cultured dorsal root ganglion (DRG) neurons. The threshold concentration of Mex was 5 mumol.L-1. The inhibitory action heightened with increasing concentrations of Mex. Complete inhibition was achieved at 150 mumol.L-1 and the 50% inhibition concentration was 31 mumol.L-1. It is suggested that the inhibition of Mex on sodium current in neurons may be one of the mechanisms of its anti-ischemic and anti-anoxic effects on the neuron.