Reactive astrocytosis in taiep rats was shown by glial fibrillary acidic protein (GFAP) immunoreactivity measured by means of enzyme-linked immunosorbent assay and indirect immunofluorescence. Increased GFAP immunoreactivity was first observed in the brainstem of 15-day-old taiep rats and was widespread throughout all brain regions at 6 months of age. Characteristically, astrocytes were hypertrophic and displayed strong GFAP fluorescence. The pattern of these reactive cells may correlate with the process of dysmyelination in the taiep rat.