Lysophosphatidic acid (LPA), a simple phospholipid, induces pain. To elucidate an involvement of ion channel mechanism in the LPA-induced pain, its effects on sodium currents in rat dorsal root ganglion (DRG) neurons were investigated. LPA suppressed tetrodotoxin-sensitive (TTX-S) sodium current, but increased tetrodotoxin-resistant (TTX-R) sodium current, when currents were evoked by step depolarizations to 0 mV from a holding potential of -80 mV. In both types of currents, LPA produced a hyperpolarizing shift of both activation and inactivation voltages. LPA had a negligible effect on the maximal conductance of TTX-S current, but increased that of TTX-R current. The results suggest that the enhancement of TTX-R current may contribute to the LPA-induced pain.