The distribution of ionic channels is thought to play an important role in the recovery of function following demyelination. Rat sciatic nerves were demyelinated by lysolecithin and single fibers were examined with patch clamp techniques. Voltage-dependent sodium currents were measured in both internodal and nodal regions. The results suggested that while there is a sharp gradient in channel density at the node of Ranvier, the total number of internodal channels far exceeds the total number of nodal channels. The nodal channels do not diffuse freely following demyelination and the internodal channels may thus serve important functions as conduction is restored.