Single-fiber preparations of the rat chorda tympani (CT) nerve were used to study the mechanism of action of capsaicin on salt-taste transduction. Capsaicin selectively suppressed the responses to NaCl of the CT nerve fibers (N-fibers) that are sodium-specific (insensitive or poorly sensitive to potassium). Among the more broadly responsive, cation-sensitive fibers (E-fibers) there are two subtypes, both of which responded to capsaicin but in different ways ('enhanced' type and 'suppressed' type). In both N- and E-fibers, 5% ethanol (the vehicle for capsaicin) slightly reduced the response to 100 mM NaCl. The suppressive effect of capsaicin on the response of the N-type fibers to 100 mM NaCl was significantly stronger than the effect of 5% ethanol. The suppression lasted for at least 20 s after the simultaneous application of 100 p.p.m. capsaicin-100 nM NaCl. These results indicate that 100 p.p.m. capsaicin can modify the response of CT fibers to NaCl. The observed effect of capsaicin on gustatory fibers could be the net result of opposite suppressive and enhancing processes in the taste buds cells and excited intra- or extragemmal trigeminal nerve endings.