Time-dependent effects of experimental diabetes and dietary myo-inositol supplementation on motor nerve conduction velocity (MNCV) were assessed in two populations of motor nerve fibers in the rat hind limb. These two populations of large myelinated motor fibers, which innervate the musculature of the calf and the foot, were differentially affected by growth, experimental diabetes, and dietary myo-inositol. Dietary myo-inositol supplementation ameliorated the diabetes-induced MNCV impairment in both nerve fiber populations but with different time courses. These observations suggest metabolic or physiologic heterogeneity among populations of large myelinated motor fibers which may partially explain published discrepancies regarding the efficacy of dietary myo-inositol supplementation in improving slowed MNCV in the streptozocin-diabetic rat.