We hypothesized that diabetic sensory neuropathy is associated with activation of apoptosis and concomitant mitochondrial dysfunction. Studies were performed in excised intact and acutely dissociated dorsal root ganglion (DRG) neurons from control and streptozotocin-induced diabetic rats with decreased peripheral nerve conduction velocities (NCV). Apoptosis was increased in acutely dissociated DRG neurons from 3- to 6-week-old diabetic rats. Basal mitochondrial membrane potential (deltapsi) was significantly more positive in DRG neurons from diabetic rats. Depolarization with glutamate resulted in significantly more positive deltapsi and delayed recovery of deltapsi in neurons from diabetic rats. Restoration of euglycemia for 2 weeks with insulin implants normalized NCV, deltapsi, and apoptosis. Intact and acutely dissociated neurons from diabetic rats demonstrated decreased Bcl-2 levels and translocation of cytochrome C from the mitochondria to the cytoplasm. Neither levels of Bax nor levels of Bcl-XL were altered in diabetic neuropathy. Apoptosis associated with mitochondrial dysfunction may contribute to the pathogenesis of diabetic sensory neuropathy.