Lafora bodies are composed of fibrillar and granular components in various concentrations. They are located in neuronal cell processes and perikarya and are frequently clearly intermingled with cytoplasmic elements. These components are electron-lucent, show a variable affinity for osmium, and are weakly stained by classical uranyl acetate stain following lead citrate. They exhibit a strong affinity for lead hydroxide and are periodic-acid reactive. They are not stained by the PTA technic for basic protein and/or acidic mucopolysaccharides. These results are in agreement with chemical studies according to which L. B are mostly composed of polyglucosans and suggest that both the granular and fibrillar ultrastructural components contain vic-glycol groups. The ultrastructure of L. B. is very similar to that of corpora amylacea, to deposits in basophilic degeneration of myocardium and in glycogenosis type IV.