Stellate cells (SCs) of entorhinal-cortex (EC) layer II are known to manifest special preference for rhythmic activity patterns characterized by predominance of the theta frequency. SCs also show subthreshold membrane resonance with marked frequency preference in the theta band. In the present study we tested the hypothesis that non- or slowly-inactivating Na⁺ currents are sufficient per se to generate resonance at near-threshold voltage levels. Whole-cell, patch-clamp experiments in the voltage-clamp mode revealed that when "threshold" Na⁺ current is activated by sinusoidal waveforms, its amplitude increases with increasing frequencies (from 0.5 to 4 Hz) of the command stimulus. This phenomenon was found to reflect the existence of an "intermediate"-kinetics component in the inactivation of the threshold Na⁺ current, characterized by a time constant of ~150-200 ms at –60 to –50 mV. In current-clamp experiments in which sinusoidal current stimulation at variable frequencies was applied, a particularly prominent membrane resonance was observed at voltage levels close to threshold (–62 to –58 mV), with a peak in the low-theta/high delta frequency region. In ~50% of the cells, such near-threshold resonance could be completely abolished by Na⁺-channel block with TTx. Our results show that in EC SCs near-threshold Na⁺ currents can be entirely responsible for membrane resonance in a voltage window where this property is most likely to influence these neurons' activity patterns.