Ranirestat (0.03-1.0 mg/kg; oral administration; once daily; for 3 weeks; male STD-Wistar rats) treatment dose-dependently decreases the elevated sorbitol and fructose levels in the rat sciatic nerves without affecting blood glucose level. Ranirestat also improves the STZ-induced decrease in motor nerve conduction velocity (MNCV) in a dose-dependent manner.