The Golgi apparatus (complex) is at the center stage of important functions of processing and transport of plasma membrane, lysosomal, and secreted proteins. The involvement of the Golgi apparatus in the pathogenesis of chronic degenerative diseases of neurons is virtually unknown. In the present study, fragmentation and atrophy of the Golgi apparatus of motor neurons in amyotrophic lateral sclerosis (ALS), has been detected with organelle specific antibodies. Approximately 30% of motor neurons in five ALS patients showed a fragmented Golgi apparatus whereas only about 1% of motor neurons from seven controls with neurologic or systemic disease showed a similar change. Morphometric studies are consistent with the hypothesis that the alteration of the Golgi apparatus is an early event in the pathogenesis of the neuronal degeneration in ALS. Immunocytochemical studies with antibodies against alpha tubulin, tau, and phosphorylated subunits of neurofilament polypeptides did not disclose differences in the staining of neurons with fragmented or normal Golgi apparatus, suggesting that the alteration of the organelle is not secondary to a gross lesion of the cytoskeleton. However, these observations do not rule out the hypothesis that the fragmentation of the Golgi apparatus is secondary to subtle changes of the polypeptides involved in the attachment of membranes of the organelle to the cytoskeleton.