Diabetic neuropathies are a family of nerve disorders caused by diabetes. Patients with diabetes can develop nerve problems at anytime, but the longer a person has diabetes the greater the risk. This study aims to investigate diabetes- and coenzyme Q10 (CoQ10) or α-lipoic acid (ALA) supplementation-induced changes in the conduction velocity (CV) distributions of rat sciatic nerve fibers. Sciatic nerve compound action potentials (CAPs) were recorded by suction electrode and CV distributions by the collision technique. Diabetes resulted in a significant increase in time to peak, rheobase and chronaxie values of these CAP waveforms, whereas the maximum depolarization, area, kinetics and CVs of bothfast and slow nerve fiber groups were found to be decreased Coenzyme Q10 (CoQ10) supplementation was found to have some positive effect on the diabetes-induced alterations. CoQ10 supplementation induced positive changes mainly in the area and fall-down phase of the kinetics of CAP waveforms. as well as rheobase, chronaxie and speed of the intermediately conducting groups (≅40 m/ s). α-Lipoic acid (ALA) supplementation did not produce statistically significant effects. This study has shown for the first time that diabetes induces a shift of actively contributing nerve fibers toward slower CVs, and supplementation with CoQ10 not only stopped this shift but also tended to restore velocities toward those of the age-matched control group. In addition to its effects on mitochondrial alterations, these positive effects of CoQ10 on diabetic neuropathy can be attributed to its antioxidant activity. Copyright 2008 Prous Science, S.A.U. or its licensors. All rights reserved.