The purpose of this study is to determine the effect of 40 mg and 80 mg ranirestat on peroneal motor nerve conduction velocity relative to placebo in subjects with mild to moderate diabetic sensorimotor polyneuropathy.

Inclusion Criteria:

• Subjects with Type 1 or Type 2, insulin-dependent or non insulin-dependent diabetes mellitus.
• Subjects with a history of distal symmetric polyneuropathy, secondary to diabetes, diagnosed in accordance with the American Academy of Neurology criteria.
• Female subjects, who are of non-reproductive potential (>=12 months post-menopausal or surgically sterile) or who are using adequate contraception which includes abstinence or double barrier methods (diaphragm and condom with spermicidal cream, intrauterine device and condom with spermicidal cream). Male subjects with partners of child-bearing potential must also use adequate contraception.
• Subjects must be able to read, understand, and provide written informed consent before enrolling in the study at screening.

Exclusion Criteria:

• History of diabetic foot ulcers or lower extremity amputation.
• Diabetic amyotrophy or non-diabetic cause of lower limb neuropathy/neuropathic symptoms.
• Clinically significant illness which, in the opinion of the investigator, would compromise a subject's suitability to participate in the study for reasons of safety or would confound the efficacy assessments.