Studies employing a bank of antisera applied to sections of LR White embedded AD and normal ageing brain tissue, may throw new light on the derivation of CA. Conspicuous levels of immunoreactivity were found in the CA of both tissues with markers for oligodendrocytic proteins such as antisera against myelin basic proteolipid protein, galactocerebroside and myelin/oligodendrocyte glycoprotein. CA were unreactive with MRC OX-42, a marker for microglia and macrophages. In a previous publication we demonstrated that the much more abundant CA in the brains of Alzheimer's disease (AD) sufferers, although slightly more varied in their immunoreactivity than those found in normally ageing controls, were universally immunoreactive with anti-tau, a neuronally derived protein and often also contained amyloid. The cores of CA were not immunoreactive with anti-GFAP, suggesting a lack of involvement with astrocytes. Our results now show that in addition to amyloid and neuronal proteins, a significant proportion of the content of CA is derived from oligodendrocytes and/or myelin. The substantial Fe peak previously reported following X-ray microanalysis of CA was probably due to ferritin. However, immunostaining with antisera to ferritin showed that high ferritin immunoreactivity was common to both micro- and macroglia as well as CA. More significantly, the immunoreactivity of CA with anti-ubiquitin suggests that degeneration of neuronal/oligodendrocytic elements may precede CA formation.