¡¾Abstract¡¿ AIM: To study the effects of temperature on mediumª²diameter primary sensory neurons in rat dorsal root ganglion (DRG). METHODS: Wholeª²cell patchª²clamp recording was performed on mediumª²diameter DRG neurons freshly isolated from rats for observing the firing characteristics by temperature gradient stimulation. RESULTS: According to the firing characteristics of the primary sensory medium neurons to the temperature changes in rat DRG, there were 2 classes of cells: In class ¢ñ, the medium neuron was temperatureª²sensitive neuron. Allª²orª²none action potentials could be generated and the number of spikes and the frequency decreased with increase of the temperature, and vice versa. The coldª²sensitive neuron was voltage dependent. In class ¢ò, the medium neuron was temperatureª²insensitive neuron. It only had single action potential with increase or decrease of the temperature, and the amplitude of the single action potential decreased with increase of the temperature. CONCLUSION: The two classes of rat DRG medium neurons have different thermosensitivity. ......