Transthyretin (TTR) binds amyloid-beta (Abeta) and prevents Abeta fibril formation in vitro. It was reported that the lack of neurodegeneration in a transgenic mouse model of Alzheimer's disease (AD) (Tg2576 mouse) was associated with increased TTR level in the hippocampus, and that chronic infusion of anti-TTR antibody into the hippocampus of Tg2576 mice led to increased local Abeta deposits, tau hyperphosphorylation and apoptosis. TTR is, therefore, speculated to prevent Abeta pathology in AD. However, a role for TTR in Abeta deposition is not yet known. To investigate the relationship between TTR and Abeta deposition, we generated a mouse line carrying a null mutation at the endogenous TTR locus and the human mutant amyloid precursor protein cDNA responsible for familial AD (Tg2576/TTR(-/-) mouse) by crossing Tg2576 mice with TTR-deficient mice. We asked whether Abeta deposition was accelerated in Tg2576/TTR(-/-) mice relative to the heterozygous mutant Tg2576 (Tg2576/TTR(+/-)) mice. Contrary to our expectations, the degree of total and vascular Abeta burdens in the aged Tg2576/TTR(-/-) mice was significantly reduced relative to the age-matched Tg2576/TTR(+/-) mice. Our experiments present, for the first time, compelling evidence that TTR does not suppress but rather accelerates vascular Abeta deposition in the mouse model of AD.