The inhibition of fibril formation of amyloid beta proteins (A beta) would be attractive therapeutic targets for the treatment of Alzheimer's disease (AD). Dopamine (DA) and other catechol derivatives were used as inhibitory factors for A beta fibril formation. The fibril formation of A beta was monitored by Thioflavin T fluorescence, a transmission electron microscopy (TEM) and a total internal reflection fluorescence microscopy (TIRFM). Catechol and its derivatives showed the dose-dependent inhibitory effects on the spontaneous A beta fibril formation. The inhibitory activity depended on the chemical structure of catechol derivatives both in the presence and absence of the liposome a model of biomembrane. Formation of catechol quinone-conjugated-A beta adduct by a Schiff-base is a key step for the inhibition effect of A beta fibril formation. (C) 2009, The Society for Biotechnology, japan. All rights reserved.