It has been observed that C-peptide administration results in an activation of renal tubular and sciatic endoneural Na/K-ATPase of the rat and stimulation of endothelial nitric oxide synthase. The hypothesis is that C-peptide administration may improve peripheral nerve dysfunction in diabetic neuropathy by increasing nerve blood flow and Na/K-ATPase activity. The purpose of the trial is to investigate the effect of C-peptide administration on diabetic peripheral sensory neuropathy in patients with type 1 diabetes and diabetic neuropathy in the lower extremities.