This study compared the relationships of the development of both Alzheimer I & II cells to reactive astrogliosis and also their distributional patterns in the demyelinated and non-demyelinated lesions in 6 cases of Wilson's disease by the use of PAP immunohistochemical technique for glial fibrillary acidic protein (GFAP). The development of GFAP positive Alzheimer I (A-I) cells was found to be directly proportional to the capability of reactive astrogliosis, and inversely proportional to the severity of Alzheimer II (A-II) change. The GFAP negative A-II cells could be identified morphologically into 2 subtypes: one with well-developed nuclei, the other with "shrunken" nuclei. They were believed to stand for the "compensatory" and "decompensatory" stages of this dynamic astrogliotic process respectively. The distribution patterns of these 2 types of astrogliosis were different: A-I cells were found only in the regions of demyelination with intensive reactive astrogliosis, while A-II cells were found diffusely in both the grey and white matter, affecting both the protoplasmic and fibrous astrocytes without special predilection.