Significantly increased glial fibrillary acidic protein (GFAP) expression was seen in postmortem brain tissue from demented patients with Alzheimer's disease (AD) (73 cases, 61 females/12 males, mean age 84 +/- 9 years) compared to controls (22 cases, 10 females/12 males, mean age 78 +/- 9 years). In demented patients, the GFAP expression, counts of AD lesions, senile/neuritic plaques (SP/NP) and neurofibrillary tangles (NFT) were higher in patients carrying the apolipoprotein E (ApoE) epsilon4 allele compared to those without the ApoE epsilon4 allele. The astrogliosis correlated significantly with the counts of NFT in demented patients both with and without the ApoE epsilon4 allele. Furthermore, the astrogliosis correlated significantly with the counts of SP/NP, but this correlation, however, was influenced by the ApoE epsilon4 allele, being significant only in those cases without the ApoE epsilon4 allele. Our results demonstrate that not only the extent of AD lesions and GFAP expression, but also the relationship between AD lesions and the GFAP expression is influenced by the ApoE epsilon4 allele.