Threshold tracking of individual polymodal C- and A -fibre terminals was used to assess membrane potential changes induced by de- or hyperpolarizing stimuli in the isolated rat skin - nerve preparation. Constant current pulses were delivered (1Hz) through a tungsten microelectrode inserted in the receptive field and the current amplitude was feedback controlled by a lab computer programmed to serially determine the electrical threshold using the method of limits. During threshold tracking, the receptive fields of the fibres were heated (32 to 46 °C in 210 s) or superfused with modified synthetic interstitial fluid containing either 0, 20, 40, 50, 60 mM [K⁺], phosphate buffer to pH 5.2 or 6.1 or bradykinin (BK, 10^-8 to 10^-5 M). High [K⁺]_e decreased the current threshold for activation by 6-14% over 120 s, whereas K⁺-free superfusion augmented the threshold by more than 5% that after some delay also induced ongoing discharge in 60% of units. pH 6.1 and 5.2 caused an increase in threshold of 6% and 18%, respectively, and 30% of the fibres were excited by low pH although the change in threshold of pH responsive and unresponsive fibres did not differ significantly, suggesting a general excitability decrease induced by protons. Heat stimulation increased the mean threshold and conduction velocity of the fibres tested and resulted in activity in 78% of units. Additionally, for these units activation was preceded by a significant decrease in threshold as compared to the tracked thresholds of fibres unresponsive to heat. Bradykinin also led to a significant threshold decrease prior to activation. In conclusion, the technique of threshold tracking proved suitable to assess changes in membrane potential resulting from receptor currents evoked by noxious heat and bradykinin in the terminal arborisation of cutaneous nociceptors.