Bis- and tris-dihydroxyaryl compounds and their methylenedioxy analogs and pharmaceutically acceptable esters, pharmaceutical compositions containing them, and their use in the treatment of amyloid diseases, especially Aβ amyloidosis, such as observed in Alzheimer's disease, use in the reduction of Aβ peptide in vivo, use in modulating APP processing, and use in modulating the activity of APP secretase.