We have described 4 patients with progressive lower and upper motor neuron deficits, marked sensory loss in the legs, 'neurogenic bladder', and, in 2 of the 4, dementia. Autopsy of two revealed a profusion of microscopic bodies resembling corpora amylacea or Lafora bodies, but restricted to processes of neurons and astrocytes. Similar (but especially large) bodies were seen within axons of sural nerves taken at biopsy from the other two patients. A general term--'polyglucosan body'--is introduced to refer to these structures in all the circumstances in which they may occur, such as in Lafora's disease, in a syndrome of longstanding double athetosis, in some cases of amyotrophic lateral sclerosis, in type IV glycogenosis, in diabetic rats, and in the normal course of ageing. Except in type IV glycogenosis, the causes for accumulation of polyglucosan bodies are unknown. They may damage tissue by more than one mechanism--probably by impeding axonal flow and impairing perivascular diffusion of metabolites.