In the present study we examined action potentials recorded from somata in the cat L7 and S1 dorsal root ganglia. We found (i) that there is a characteristic spike duration for each receptor type (e.g. Golgi tendon organ, D-hair) and (ii) that, for a given peripheral fiber conduction velocity, somata whose axons supply low-threshold cutaneous receptors exhibit spikes with shorter durations than those innervating high-threshold cutaneous receptors. These results suggest that there may be significant differences in somal membrane composition which are specific to the physiological receptor types innervated.