The presence and distribution of apoptotic cell death in multiple system atrophy (MSA) and morphologically related diseases were investigated by means of a modified terminal deoxynucleotidyl transferase-mediated nick end labeling method, comparing their distribution with that of glial cytoplasmic inclusions, immunohistochemically demonstrated bcl-2 protein, bax protein, CD95, TNFalpha, and p53-protein expression, as well as activated microglia. Apoptosis occurred almost exclusively in oligodendrocytes in multiple system atrophy and its general distribution was comparable to the already known oligodendroglial pathology in this disorder. Additionally, in about a quarter of glial cytoplasmic inclusions, there was upregulation of bcl-2-protein and coexpression with ubiquitin, suggesting a final attempt of involved cells to counteract apoptotic cell death. Bax protein was also demonstrated in oligodendroglial cells. A significant neuronal apoptosis was not observed in MSA; these cells might be destroyed secondarily to oligodendroglial apoptosis by necrosis or other forms of programmed cell death. These results emphasize the central role of oligodendroglial pathology in multiple system atrophy, making this disease unique among neurodegenerative diseases.