In the somatic membrane of acutely isolated newborn rat dorsal root ganglion neurons four inward and three outward currents were separated on the basis of their different voltage dependence and kinetic properties. The capacity of their membrane was measured for 136 investigated neurons. Neurons were separated according to capacities of their somata for three subpopulations: small 26.5 pF, medium 41.5 pF and large 61.4 pF. Neurons with TTX-insensitive sodium current were from medium and, partially, from small subpopulations. Neurons with low threshold calcium current were from large and, partially, from medium subpopulations.