In studies of nerve excitation it is important to examine the possible interaction of voltage-sensitive gating mechanisms with components forming the pathway of ionic channels. There is evidence that permeant ions and gating are independent in Na+ channels1,2 of nerve fibres, but not in K+ channels3. Of interest in this and other studies of excitability is the determination of the physical basis for the resistance in series with the axon membrane (Rs)4. In an attempt to determine whether an appreciable Rs is associated with individual Na+ channels5, we have compared gating kinetics in conditions in which the ionic current through individual channels is varied while the total membrane current remains constant. The number of conducting Na+ channels, and thus their contribution to Rs, was lowered by addition of tetrodotoxin6. We report here that no more than 10% of the resistance in ‘series’ with activation gates is associated with the Na+ channel, and give some preliminary estimates for minimum distances between gates and ion-binding sites within the Na+ channel.