AD is associated with amyloid deposition of the cerebral vasculature (cerebral amyloid angiopathy; CAA). The ϵ4 allele of ApoE is a risk factor for AD and may cause vascular disruption, suggesting enhanced susceptibility in individuals carrying this allele. Using human ApoE2, ApoE3, and ApoE4 knock-in mice bred to an AD-transgenic mouse model, we are investigating the hemorrhage rate and underlying mechanism of BBB damage.