The effect of derivatives of sulfur dioxide (SO 2 ), a common air pollutant, which exists in vivo at equilibrium between bisulfate and sulfite, was studied on hyperpolarization-activated cation current (I h ) in cultured post-natal dorsal root ganglion (DRG) neurons using the whole cell configuration of patch-clamp technique. SO 2 derivatives increased I h current in a dose and voltage-dependent manner. The EC 50 value was 25μM and the Hill coefficient was 1.44. 50μM SO 2 derivatives significantly shifted the activation curve of I h in the hyperpolarizing direction by 5.5mV. The reversal potential of I h was shifted to 5.2mV in positive direction by 10μM SO 2 derivatives. According to the functional role of I h , the increase of I h should result in an enhanced neuronal excitability, which was possibly the basis for neuropathic pain.