We have applied modem techniques to extend the range of Po measurement below ~10 -7. The use of a skeletal muscle Na § channel clone deficient in fast inactivation permitted measurement of steady currents in the hyperpolarized range of potentials, and single-channel recording permitted detection of very brief open events even when very rare. Mean-Variance analysis (Patlak, 1993) was used, in part, to process hundreds of megabytes of **data** in order to facilitate analysis but maintain demonstrable quality. Our results show a limiting slope for Na § channels that is twice as steep as previously suspected, with a minimum transfer of 12 charges needed to open these Na + channels. These results have major implications for our understanding of Na + channel gating, for the estimates of the number of gates actively involved, and for the interpretation of mutagenesis experiments.