The concentration of axons in the pyramidal tract of normal and spinal cord-injured rats was determined by counting axons in sections of spinal cord stained by the Holmes technique. In the normal rat the axon concentration was uniform in the cervical, thoracic, and lumbar regions, although the size of the tract diminished progressively with its descent in the cord. After acute cord transection or compression injury, the axon concentration distal to the injury site diminished markedly. However, an appreciable number of distal axons persisted after injury, due to either delayed degeneration or to the presence of an admixture of afferent fibers. The axonal counting technique developed in this study should be helpful in experiments on spinal cord injury and regeneration.