These studies lead us to propose the following hypothesis. The earliest change in the axon following hexacarbon exposure is an alteration in the cytoskeleton, resulting in clusters of microtubule channels segregated from neurofilaments. Initially, fast anterograde transport continues through these functioning channels. With continued exposure, the cytoskeleton becomes chaotic, and pathways for moving organelles are impaired, affecting both anterograde and retrograde transport. The severe disruption in axoplasmic transport seems to play a key role in axonal degeneration, at least in part related to the failure of delivery of important materials to the distal axon. Furthermore, the accumulation of lysosomal material, carried by retrograde transport, may play a role in the initiation andor acceleration of the intraaxonal digestive process which is part of nerve fiber degeneration.