A new technique for the simultaneous internal dialysis and voltage-clamp of Myxicola axons is described and shown to control the internal composition of the axon adequately. 2. The permeability ratio (PNa/PK) of the sodium channel is 15.5 in axons dialysed with sodium-free solutions, somewhat higher than observed in perfused axons. 3. Asymmetry currents are easily recorded in dialysed Myxicola axons. At 4--5 degrees C for pulse durations sufficiently short Qon = Qoff with a maximum charge displacement of 10 nC/cm2 and half the charge being displaced by a step to -32 mV. Maximum slope of the Q(V) curve is 15 mV/e-fold change in charge displaced. The time constant tau on reaches a maximum of 325 microseconds at a potential of -23 mV. 4. The time course of sodium activation cannot be adequately accounted for by (Q/Q infinity) X using any single value of X for potentials between -40 and 40 MV. 5. Both asymmetry currents and INa are inactivated by the same amount when Myxicola axons are repetitively depolarized at frequencies from 0.1 to 50 Hz.
