Oxidative stress and neurovascular dysfunction have emerged as contributing factors to the development of experimental diabetic neuropathy (EDN) in streptozotocin-diabetic (STZ-D) rodents. Additionally depletion of C-peptide has been implicated in the pathogenesis of EDN, but the mechanisms of these effects have not been fully characterized. The aims of this study were therefore to explore the effects of diabetes on neurovascular dysfunction and indices of nerve oxidative stress in Type 1 BB/Wor-rats and Type 2 BBZDR/Wor-rats and to determine the effects of C-peptide replacement in the former. Motor and sensory nerve conduction velocities (NCV's), hind limb thermal thresholds, endoneurial blood flow, and indicators of oxidative stress were evaluated in nondiabetic control rats, BB/Wor-rats, BB/Wor-rats replaced with rat-II C-peptide (75 nmol C-peptide/kg body weight/day) for 2 mo and diabetes-duration matched BBZDR/Wor-rats. Endoneurial perfusion was decreased and oxidative stress increased in type 1 BB/Wor-rats. C-peptide prevented NCV and neurovascular deficits and attenuated thermal hyperalgesia. Inhibition of nitric oxide (NO) synthase but not cyclooxygenase, reversed the C-peptide-mediated effects on NCV and nerve blood flow. Indices of oxidative stress were unaffected by C-peptide. In type 2 BBZDR/Wor-rats, neurovascular deficits and increased oxidative stress were unaccompanied by sensory NCV slowing or hyperalgesia. Therefore nerve oxidative stress is increased and endoneurial perfusion decreased in type 1 BB/Wor and Type 2 BBZDR/Wor-rats. NO and neurovascular mechanisms, but not oxidative stress, appear to contribute to the effects of C-peptide in Type 1 EDN. Sensory nerve deficits are not an inevitable consequence of increased oxidative stress and decreased nerve perfusion in a type 2 diabetic rodent model.