Tetrodotoxin-sensitive and tetrodotoxin-resistant sodium currents were studied in rat dorsal root ganglion neurons using a patch-clamp method. The type of hydrogen ion buffer used was found to affect the kinetics of the inactivation process. Tris ions irreversibly bound to the inactivation gating apparatus, accelerating the decay in the trailing front of the ion current. The characteristics of this process were clearly nonlinear in this buffer. In HEPES buffer, the inactivation dynamics were slowed for both types of channel studied. Unlike results obtained with tris buffer, there were no sharp changes in the characteristics as compared to those obtained immediately after puncture of the cell membrane. The advantages of using HEPES buffer for studies of the inactivation gating processes of sodium channels are discussed.