The deposition of amyloid beta protein (Abeta), a proteolytic cleavage product of amyloid precursor protein (APP), is an invariable pathological feature of the Alzheimer's disease brain, while APP gene is widely expressed in all neuronal and non-neuronal tissues with the highest levels of expression in the brain, and kidney. To understand the role transthyretin (TTR) plays in the sequestration mechanism of Abeta in the kidney, we have investigated interactions of TTR with Abeta1-40 and Abeta1-42 molecules by an immunoprecipitation method, in vitro binding studies, and overlay assay. These in vivo and in vitro biochemical experiments showed that TTR bound Abeta1-42 preferentially, and Abeta1-40 only to a limited extent, to form TTR-monomer and -dimer-Abeta complexes in the normal human kidney. We provide new evidence supporting the hypothesis that TTR, an Abeta binding protein, plays an important role in the sequestration of Abeta and prevents amyloid formation in the kidney.