Slow electrical responses after painful stimulation with carbon dioxide, which is known to specifically activate nociceptors, were recorded from the nasal respiratory epithelium in human volunteers. The negative component of these potentials (negative mucosal potential NMP) has been hypothesized to be a summated receptor potential. The aim of the present study was to characterize the stimulus-response relationship and to demonstrate that the NMP is restricted to the site of stimulation, i.e., to the area of activated nociceptors. Eight healthy volunteers participated in the experiments. The NMP was recorded from the nasal septum and intensity ratings were obtained for each of the applied stimuli. To control for autonomic reflexes, blood flow changes were additionally recorded using a laser Doppler flow meter. Both increasing stimulus duration and increasing concentration produced a significant increase in the subjects' intensity estimates, in the NMP's amplitudes and areas under the curve, but did not change the local blood flow in a dose-related manner. The odorant hydrogen sulphide, which was used as a non-painful control stimulus, did not elicit mucosal potentials or produce blood flow changes. By recording both ipsi- and contralaterally it was also demonstrated that the NMP could only be obtained at the stimulated site, thus supporting the hypothesis that the NMP is a specific peripheral nociceptive correlate.