Intracellular recordings were obtained from primary sensory neurons in excised dorsal root ganglia (DRGs). Most (90%) neurons sampled became depolarized during periods of repetitive stimulation of a branch of the dorsal root (DR) which contained only axons of neighboring neurons. DR stimulation also evoked a transient rise in extracellular K+ concentration ([K+]o), following similar kinetics. Thus, the mutual excitation among DRG neurons may be mediated by [K+]o. Activity-dependent cross-excitation in DRGs could contribute to neuropathic sensory abnormalities often triggered by nerve injury or disease.