The electron microscope has been used to examine a diagnostic biopsy of frontal neocortex which showed the light microscopic features of Alzheimer's disease. In addition to plaques and tangles, the biopsy showed some neurons which contained abnormal tubular profiles specifically associated with their granular endoplasmic reticulum. In transverse section the profiles consisted of two concentric layers of trilaminar unit membrane with an overall diameter of approximately 75 nm and they appeared to lie within the cisternae of granular endoplasmic reticulum. When cut longitudinally, the structures appeared as elongated tubes lying within the endoplasmic reticulum, but a number of ends were found where the inner membrane formed a closed tube and the outer membrane folded back and was continuous with the membrane forming the outer layer of the sac of endoplasmic reticulum. These profiles do not appear to have been described previously although similarities between their ultrastructure and that of the coat of certain unusual forms of Rhabdovirus are noted.