Glial cytoplasmic inclusions (GCIs) were demonstrated by silver staining, immunocytochemistry and by electron microscopy in the central nervous system (CNS) of 11 patients with various combinations of striatonigral degeneration, olivopontocerebellar atrophy and Shy-Drager syndrome. Although their configuration in light microscope can sometimes resemble neurofibrillary tangles, their cellular localisation, measurements, ultrastructure, immunocytochemical characteristics and regional distribution all differ from these Alzheimer type changes. The majority of GCIs were localized in the white matter and appeared to be accompanied by an increase in the number of interfascicular oligodendroglial cells and pallor or loss of myelin staining. Our histological, ultrastructural and immunocytochemical findings all indicate that the cells which contain GCIs are oligodendrocytes and the inclusions themselves are composed of tubular structures. The presence of the until now unknown GCIs in all the 11 CNS, but not in age- and sex-matched control brains, indicates that GCI is a cellular change characteristic of multiple system atrophy and the three syndromes are various manifestations of the same disease.