HEAD injury is one of the potential environmental factors in Alzheimer's disease (AD). To study the chronic stage of concussive brain injury, histological analyses were performed 2–6 months after right lateral fluid percussion (FP) brain injury (3.6–4.8 atm) in rats. Six months after injury, numerous normal-looking neurons in the telencephalon and brain stem were immunoreactive with either antibody to phosphorylated tau or with four antibodies to β-amyloid protein. Neuronal counts in the cortices were gradually decreased after injury, up to 42% loss at 6 months after injury. These neuropathological changes suggest that this animal model could serve as a good animal model of neurodegenerative diseases such as AD.