Charge movements in intact frog twitch fibres were studied using a three-microelectrode voltage-clamp technique. When high potassium solution was applied transiently to the muscle fibres at low temperature in the presence of D600, the fibres became paralysed and, concomitantly, charge movement disappeared. The amount of charge suppressed by the paralysis treatment was about 70-100% of that in control experiments. This paralysing action of D600 is not shared by its derivative D890. The requirement of conditioning potassium contracture is, most likely, related to prolonged membrane depolarization, as voltage-clamped depolarization to 0 mV lasting tens of seconds also suppressed charge movement. When paralysed fibres were warmed, the main charge component (Q beta) was reprimed. By contrast, the hump charge component (Q gamma) was only reprimed in some of the fibres. Other than by warming, as paralysed fibre could be revived by stimulating it with large suprathreshold pulses but not by voltage-clamped hyperpolarization to -160 mV for tens of seconds. The paralysing action of D600 described here appears to be unrelated to its ability in blocking Ca2+ channels.