Although the causative genetic mutations for a subset of some of the most prevalent human motor neurodegenerative diseases have been identified, the exact molecular mechanisms behind motor neuron and associated muscular loss in these disorders remain an unsolved mystery. In a recent issue of Science, two mutagenesis-derived mouse mutants are described that contain missense mutations in the gene encoding the cytoplasmic dynein heavy-chain protein, which is part of a major cellular motor complex involved in retrograde axonal transport. These mutations result in progressive motor neuron degeneration in heterozygous animals and Lewy-like inclusion bodies in the homozygotes resembling those that occur in related human pathologies such as amyotrophic lateral sclerosis, spinal muscular atrophy, and spinal-bulbar muscular atrophy. This discovery opens up the exciting possibility that similar mutations may be involved in these human disease states.