To understand the significance of the accumulation of alpha B-crystallin in Rosenthal fibers within astrocytes, the expression and metabolism of alpha B-crystallin in glioma cell lines were examined under the conditions of heat and oxidative stress. alpha B-crystallin mRNA was increased after both stresses, and alpha B-crystallin protein moved from a detergent-soluble to a detergent-insoluble form. In addition, Western blotting of Alexander's disease brain homogenates revealed that the 27-kd heat shock protein (HSP27), which is related to alpha B-crystallin, accumulates along with alpha B-crystallin. The presence of HSP27 in Rosenthal fibers was directly demonstrated by immunohistochemistry. Our results suggest that astrocytes in Alexander's disease may be involved in an as yet unknown kind of stress reaction that causes the accumulation of alpha B-crystallin and HSP27 and results in Rosenthal fiber formation.