Thirty-three rectus superior extraocular muscles from 23 autopsy cases, all over 60 years, were examined. Eosinophilic inclusions (Hirano bodies) were observed in all the muscles; they were stained deep red by Masson's trichrome stain and were positive for protein stain. They consisted of a collection of filamentous structures of two types: (1) a regular array of filaments 100 A in diameter which sometimes were arrayed in perpendicular planes and (2) another type in a herring bone or ladder-like pattern. Both structures were closely associated with the accumulated thin filaments 50-60 A in diameter (actin?) in the subsarcolemma. The frequent appearance in aged muscle fibers of Hirano bodies indicates that their formation is a change closely related with aging.