BSB, derived from the structure of Congo Red, is shown to bind to a wide range of amyloid inclusions in situ. More importantly it is also used to label brain amyloids in live animals. BSB recognizes amyloid lesions, and has distinctive properties which allow the quantitative monitoring of the formation of amyloid fibrils assembled from the Ab peptide, a-synuclein and tau. It is a cell-permeable fluorescent probe that specifically binds to and labels intracellular b-amyloid aggregates both in vitro (Ki = 400 nM) and in vivo. It is also used as an antemortem diagnostic tool for animal models of Alzheimer’s disease.