Dorsal root ganglion (DRG) is composed of neuronal cell bodies of primary afferents with diverse functions. Various types of ion channels present on DRG neurons may reflect those functions. In the present study, voltage-gated potassium currents in DRG neurons of neonatal rats were characterized by whole-cell voltage clamp method. Two types of delayed rectifier and three types of transient potassium currents were identified according to their electrophysiological properties. The delayed rectifier currents were named IKe (early inactivating) and IKl (late inactivating). Steady state inactivation of IKe began from -100 mV lasting until ⁣20 mV. IKl could be distinguished from IKe by its inactivation voltage range, from -70 mV to +10 mV. Three transient currents were named IAf (fast inactivation), IAi (intermediate inactivation kinetics), and IAs (slow inactivation). IAf showed fast inactivation with time constant of 10.6±2.0 msec, IAi of 36.9±13.9 msec, and IAs of 60.6±2.9 msec at ⁢30 mV, respectively. They also had distinct steady state inactivation range of each. Each cell expressed diverse combination of potassium currents. The cells most frequently observed were those which expressed both IKl and IAf, and they had large diameters. The cells expressing IKe and expressing IKe, IAi, and IAs usually had small diameters. Judging from cell diameter, capsaicin sensitivity or action potential duration, candidates for nociceptor were the cells expressing IKe, expressing IKe and IAi, and expressing IKe and IAs. The types and distribution of potassium currents in neonatal rat DRG were similar to those of adult rat DRG (Gold et al, 1996b).