The microtubule-associated protein tau plays a critical role in many neurodegenerative diseases, including Alzheimer’s disease. Abnormal hyperphosphorylation of tau (pTau) generates pathological paired helical filaments (PHF) that aggregate into neurofibrillary tangles, which leads to a cascade of changes including neuroinflammation and network excitability. Abnormal pTau, neuroinflammation, and seizures also occur in patients with glioblastoma (GBM) and recent work suggests pTau may be a potential a link between neurodegenerative changes and glioblastoma.Using live adult human cortical tissue obtained from tumour patients undergoing neurosurgical resection we have optimised the development of organotypic brain slice cultures maintained for up to 21 days in vitro (DIV). Tau preformed fibrils (pff) containing the P301L mutation were added to a proportion of cultures on DIV0/1 and both control and fibril-treated slices were fixed at DIV21/22. Immunohistochemistry was used to detect pTau (PHF-1), neurons (NeuN, MAP2), and glia (IBA1, GFAP) and sections were imaged using confocal microscopy.Initial results show that fibril-treated and control slice cultures express pTau in neurons, astrocytes and blood vessels. We found subject and slice variability in the levels of pTau expression as indicated by PHF-1 staining. We are exploring the links between patient age, disease status, sex and history of seizures to identify the causes of different pTau expression levels. Our results show we can maintain a human organotypic cortical brain slice platform that expresses both endogenous pTau and fibril-induced pTau. Ongoing studies are investigating the correlation between glial reactivity, cell death, network excitability and pTau levels.